gmqcc/fold.c

/*
 * Copyright (C) 2012, 2013, 2014
 *     Dale Weiler
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of
 * this software and associated documentation files (the "Software"), to deal in
 * the Software without restriction, including without limitation the rights to
 * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
 * of the Software, and to permit persons to whom the Software is furnished to do
 * so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
#include <string.h>
#include <math.h>

#include "ast.h"
#include "parser.h"

#define FOLD_STRING_UNTRANSLATE_HTSIZE 1024
#define FOLD_STRING_DOTRANSLATE_HTSIZE 1024

/*
 * The constant folder is also responsible for validating if the constant
 * expressions produce valid results. We cannot trust the FPU control
 * unit for these exceptions because setting FPU control words might not
 * work. Systems can set and enforce FPU modes of operation. It's also valid
 * for libc's to simply ignore FPU exceptions. For instance ARM CPUs in
 * glibc. We implement some trivial and IEE 754 conformant functions which
 * emulate those operations. This is an entierly optional compiler feature
 * which shouldn't be enabled for anything other than performing strict
 * passes on constant expressions since it's quite slow.
 */
typedef uint32_t sfloat_t;

typedef union {
    qcfloat_t f;
    sfloat_t  s;
} sfloat_cast_t;

typedef enum {
    SFLOAT_INVALID   = 1,
    SFLOAT_DIVBYZERO = 4,
    SFLOAT_OVERFLOW  = 8,
    SFLOAT_UNDERFLOW = 16,
    SFLOAT_INEXACT   = 32
} sfloat_exceptionflags_t;

typedef enum {
    SFLOAT_ROUND_NEAREST_EVEN,
    SFLOAT_ROUND_DOWN,
    SFLOAT_ROUND_UP,
    SFLOAT_ROUND_TO_ZERO
} sfloat_roundingmode_t;

typedef enum {
    SFLOAT_TAFTER,
    SFLOAT_TBEFORE
} sfloat_tdetect_t;

typedef struct {
    sfloat_roundingmode_t   roundingmode;
    sfloat_exceptionflags_t exceptionflags;
    sfloat_tdetect_t        tiny;
} sfloat_state_t;

/* The value of a NaN */
#define SFLOAT_NAN 0xFFC00000
/* Count of leading zero bits before the most-significand 1 bit. */
#define SFLOAT_CLZ(X, SUB) \
    (__builtin_clz((X)) - (SUB))
/* Test if NaN */
#define SFLOAT_ISNAN(A) \
    (0xFF000000 < (uint32_t)((A) << 1))
/* Test if signaling NaN */
#define SFLOAT_ISSNAN(A) \
    (((((A) >> 22) & 0x1FF) == 0x1FE) && ((A) & 0x003FFFFF))
/* Raise exception */
#define SFLOAT_RAISE(STATE, FLAGS) \
    ((STATE)->exceptionflags |= (FLAGS))
/*
 * Shifts `A' right `COUNT' bits. Non-zero bits are stored in LSB. Size
 * sets the arbitrarly-large limit.
 */
#define SFLOAT_SHIFT(SIZE, A, COUNT, Z)                                      \
    *(Z) = ((COUNT) == 0)                                                    \
        ? 1                                                                  \
        : (((COUNT) < (SIZE))                                                \
            ? ((A) >> (COUNT)) | (((A) << ((-(COUNT)) & ((SIZE) - 1))) != 0) \
            : ((A) != 0))
/* Extract fractional component */
#define SFLOAT_EXTRACT_FRAC(X) \
    ((uint32_t)((X) & 0x007FFFFF))
/* Extract exponent component */
#define SFLOAT_EXTRACT_EXP(X) \
    ((int16_t)((X) >> 23) & 0xFF)
/* Extract sign bit */
#define SFLOAT_EXTRACT_SIGN(X) \
    ((X) >> 31)
/* Normalize a subnormal */
#define SFLOAT_SUBNORMALIZE(SA, Z, SZ) \
    (void)(*(SZ) = (SA) << SFLOAT_CLZ((SA), 8), *(SZ) = 1 - SFLOAT_CLZ((SA), 8))
/*
 * Pack sign, exponent and significand and produce a float.
 *
 * Integer portions of the significand are added to the exponent. The
 * exponent input should be one less than the result exponent whenever
 * the significand is normalized since normalized significand will
 * always have an integer portion of value one.
 */
#define SFLOAT_PACK(SIGN, EXP, SIG) \
    (sfloat_t)((((uint32_t)(SIGN)) << 31) + (((uint32_t)(EXP)) << 23) + (SIG))

/* Calculate NaN. If either operands are signaling then raise invalid */
static sfloat_t sfloat_propagate_nan(sfloat_state_t *state, sfloat_t a, sfloat_t b) {
    bool isnan_a  = SFLOAT_ISNAN(a);
    bool issnan_a = SFLOAT_ISSNAN(a);
    bool isnan_b  = SFLOAT_ISNAN(b);
    bool issnan_b = SFLOAT_ISSNAN(b);

    a |= 0x00400000;
    b |= 0x00400000;

    if (issnan_a | issnan_b)
        SFLOAT_RAISE(state, SFLOAT_INEXACT);
    if (issnan_a) {
        if (issnan_b)
            goto larger;
        return isnan_b ? b : a;
    } else if (isnan_a) {
        if (issnan_b | !isnan_b)
            return a;
larger:
        if ((uint32_t)(a << 1) < (uint32_t)(b << 1)) return b;
        if ((uint32_t)(b << 1) < (uint32_t)(a << 1)) return a;
        return (a < b) ? a : b;
    }
    return b;
}

/* Round and pack */
static sfloat_t SFLOAT_PACK_round(sfloat_state_t *state, bool sign_z, int16_t exp_z, uint32_t sig_z) {
    sfloat_roundingmode_t mode      = state->roundingmode;
    bool                  even      = !!(mode == SFLOAT_ROUND_NEAREST_EVEN);
    unsigned char         increment = 0x40;
    unsigned char         bits      = sig_z & 0x7F;

    if (!even) {
        if (mode == SFLOAT_ROUND_TO_ZERO)
            increment = 0;
        else {
            increment = 0x7F;
            if (sign_z) {
                if (mode == SFLOAT_ROUND_UP)
                    increment = 0;
            } else {
                if (mode == SFLOAT_ROUND_DOWN)
                    increment = 0;
            }
        }
    }

    if (0xFD <= (uint16_t)exp_z) {
        if ((0xFD < exp_z) || ((exp_z == 0xFD) && ((int32_t)(sig_z + increment) < 0))) {
            SFLOAT_RAISE(state, SFLOAT_OVERFLOW | SFLOAT_INEXACT);
            return SFLOAT_PACK(sign_z, 0xFF, 0) - (increment == 0);
        }
        if (exp_z < 0) {
            /* Check for underflow */
            bool tiny = (state->tiny == SFLOAT_TBEFORE) || (exp_z < -1) || (sig_z + increment < 0x80000000);
            SFLOAT_SHIFT(32, sig_z, -exp_z, &sig_z);
            exp_z = 0;
            bits = sig_z & 0x7F;
            if (tiny && bits)
                SFLOAT_RAISE(state, SFLOAT_UNDERFLOW);
        }
    }

    /*
     * Significand has point between bits 30 and 29, 7 bits to the left of
     * the usual place. This shifted significand has to be normalized
     * or smaller, if it isn't the exponent must be zero, in which case
     * no rounding occurs since the result will be a subnormal.
     */
    if (bits)
        SFLOAT_RAISE(state, SFLOAT_INEXACT);
    sig_z = (sig_z + increment) >> 7;
    sig_z &= ~(((bits ^ 0x40) == 0) & even);
    if (sig_z == 0)
        exp_z = 0;
    return SFLOAT_PACK(sign_z, exp_z, sig_z);
}

/* Normalized round and pack */
static sfloat_t SFLOAT_PACK_normal(sfloat_state_t *state, bool sign_z, int16_t exp_z, uint32_t sig_z) {
    unsigned char c = SFLOAT_CLZ(sig_z, 1);
    return SFLOAT_PACK_round(state, sign_z, exp_z - c, sig_z << c);
}

static sfloat_t sfloat_add_impl(sfloat_state_t *state, sfloat_t a, sfloat_t b, bool sign_z) {
    int16_t  exp_a = SFLOAT_EXTRACT_EXP(a);
    int16_t  exp_b = SFLOAT_EXTRACT_EXP(b);
    int16_t  exp_z = 0;
    int16_t  exp_d = exp_a - exp_b;
    uint32_t sig_a = SFLOAT_EXTRACT_FRAC(a) << 6;
    uint32_t sig_b = SFLOAT_EXTRACT_FRAC(b) << 6;
    uint32_t sig_z = 0;

    if (0 < exp_d) {
        if (exp_a == 0xFF)
            return sig_a ? sfloat_propagate_nan(state, a, b) : a;
        if (exp_b == 0)
            --exp_d;
        else
            sig_b |= 0x20000000;
        SFLOAT_SHIFT(32, sig_b, exp_d, &sig_b);
        exp_z = exp_a;
    } else if (exp_d < 0) {
        if (exp_b == 0xFF)
            return sig_b ? sfloat_propagate_nan(state, a, b) : SFLOAT_PACK(sign_z, 0xFF, 0);
        if (exp_a == 0)
            ++exp_d;
        else
            sig_a |= 0x20000000;
        SFLOAT_SHIFT(32, sig_a, -exp_d, &sig_a);
        exp_z = exp_b;
    } else {
        if (exp_a == 0xFF)
            return (sig_a | sig_b) ? sfloat_propagate_nan(state, a, b) : a;
        if (exp_a == 0)
            return SFLOAT_PACK(sign_z, 0, (sig_a + sig_b) >> 6);
        sig_z = 0x40000000 + sig_a + sig_b;
        exp_z = exp_a;
        goto end;
    }
    sig_a |= 0x20000000;
    sig_z = (sig_a + sig_b) << 1;
    --exp_z;
    if ((int32_t)sig_z < 0) {
        sig_z = sig_a + sig_b;
        ++exp_z;
    }
end:
    return SFLOAT_PACK_round(state, sign_z, exp_z, sig_z);
}

static sfloat_t sfloat_sub_impl(sfloat_state_t *state, sfloat_t a, sfloat_t b, bool sign_z) {
    int16_t  exp_a = SFLOAT_EXTRACT_EXP(a);
    int16_t  exp_b = SFLOAT_EXTRACT_EXP(b);
    int16_t  exp_z = 0;
    int16_t  exp_d = exp_a - exp_b;
    uint32_t sig_a = SFLOAT_EXTRACT_FRAC(a) << 7;
    uint32_t sig_b = SFLOAT_EXTRACT_FRAC(b) << 7;
    uint32_t sig_z = 0;

    if (0 < exp_d) goto exp_greater_a;
    if (exp_d < 0) goto exp_greater_b;

    if (exp_a == 0xFF) {
        if (sig_a | sig_b)
            return sfloat_propagate_nan(state, a, b);
        SFLOAT_RAISE(state, SFLOAT_INVALID);
        return SFLOAT_NAN;
    }

    if (exp_a == 0)
        exp_a = exp_b = 1;

    if (sig_b < sig_a) goto greater_a;
    if (sig_a < sig_b) goto greater_b;

    return SFLOAT_PACK(state->roundingmode == SFLOAT_ROUND_DOWN, 0, 0);

exp_greater_b:
    if (exp_b == 0xFF)
        return (sig_b) ? sfloat_propagate_nan(state, a, b) : SFLOAT_PACK(sign_z ^ 1, 0xFF, 0);
    if (exp_a == 0)
        ++exp_d;
    else
        sig_a |= 0x40000000;
    SFLOAT_SHIFT(32, sig_a, -exp_d, &sig_a);
    sig_b |= 0x40000000;
greater_b:
    sig_z = sig_b - sig_a;
    exp_z = exp_b;
    sign_z ^= 1;
    goto end;

exp_greater_a:
    if (exp_a == 0xFF)
        return (sig_a) ? sfloat_propagate_nan(state, a, b) : a;
    if (exp_b == 0)
        --exp_d;
    else
        sig_b |= 0x40000000;
    SFLOAT_SHIFT(32, sig_b, exp_d, &sig_b);
    sig_a |= 0x40000000;
greater_a:
    sig_z = sig_a - sig_b;
    exp_z = exp_a;

end:
    --exp_z;
    return SFLOAT_PACK_normal(state, sign_z, exp_z, sig_z);
}

static GMQCC_INLINE sfloat_t sfloat_add(sfloat_state_t *state, sfloat_t a, sfloat_t b) {
    bool sign_a = SFLOAT_EXTRACT_SIGN(a);
    bool sign_b = SFLOAT_EXTRACT_SIGN(b);
    return (sign_a == sign_b) ? sfloat_add_impl(state, a, b, sign_a)
                              : sfloat_sub_impl(state, a, b, sign_a);
}

static GMQCC_INLINE sfloat_t sfloat_sub(sfloat_state_t *state, sfloat_t a, sfloat_t b) {
    bool sign_a = SFLOAT_EXTRACT_SIGN(a);
    bool sign_b = SFLOAT_EXTRACT_SIGN(b);
    return (sign_a == sign_b) ? sfloat_sub_impl(state, a, b, sign_a)
                              : sfloat_add_impl(state, a, b, sign_a);
}

static sfloat_t sfloat_mul(sfloat_state_t *state, sfloat_t a, sfloat_t b) {
    int16_t  exp_a   = SFLOAT_EXTRACT_EXP(a);
    int16_t  exp_b   = SFLOAT_EXTRACT_EXP(b);
    int16_t  exp_z   = 0;
    uint32_t sig_a   = SFLOAT_EXTRACT_FRAC(a);
    uint32_t sig_b   = SFLOAT_EXTRACT_FRAC(b);
    uint32_t sig_z   = 0;
    uint64_t sig_z64 = 0;
    bool     sign_a  = SFLOAT_EXTRACT_SIGN(a);
    bool     sign_b  = SFLOAT_EXTRACT_SIGN(b);
    bool     sign_z  = sign_a ^ sign_b;

    if (exp_a == 0xFF) {
        if (sig_a || ((exp_b == 0xFF) && sig_b))
            return sfloat_propagate_nan(state, a, b);
        if ((exp_b | sig_b) == 0) {
            SFLOAT_RAISE(state, SFLOAT_INVALID);
            return SFLOAT_NAN;
        }
        return SFLOAT_PACK(sign_z, 0xFF, 0);
    }
    if (exp_b == 0xFF) {
        if (sig_b)
            return sfloat_propagate_nan(state, a, b);
        if ((exp_a | sig_a) == 0) {
            SFLOAT_RAISE(state, SFLOAT_INVALID);
            return SFLOAT_NAN;
        }
        return SFLOAT_PACK(sign_z, 0xFF, 0);
    }
    if (exp_a == 0) {
        if (sig_a == 0)
            return SFLOAT_PACK(sign_z, 0, 0);
        SFLOAT_SUBNORMALIZE(sig_a, &exp_a, &sig_a);
    }
    if (exp_b == 0) {
        if (sig_b == 0)
            return SFLOAT_PACK(sign_z, 0, 0);
        SFLOAT_SUBNORMALIZE(sig_b, &exp_b, &sig_b);
    }
    exp_z = exp_a + exp_b - 0x7F;
    sig_a = (sig_a | 0x00800000) << 7;
    sig_b = (sig_b | 0x00800000) << 8;
    SFLOAT_SHIFT(64, ((uint64_t)sig_a) * sig_b, 32, &sig_z64);
    sig_z = sig_z64;
    if (0 <= (int32_t)(sig_z << 1)) {
        sig_z <<= 1;
        --exp_z;
    }
    return SFLOAT_PACK_round(state, sign_z, exp_z, sig_z);
}

static sfloat_t sfloat_div(sfloat_state_t *state, sfloat_t a, sfloat_t b) {
    int16_t  exp_a   = SFLOAT_EXTRACT_EXP(a);
    int16_t  exp_b   = SFLOAT_EXTRACT_EXP(b);
    int16_t  exp_z   = 0;
    uint32_t sig_a   = SFLOAT_EXTRACT_FRAC(a);
    uint32_t sig_b   = SFLOAT_EXTRACT_FRAC(b);
    uint32_t sig_z   = 0;
    bool     sign_a  = SFLOAT_EXTRACT_SIGN(a);
    bool     sign_b  = SFLOAT_EXTRACT_SIGN(b);
    bool     sign_z  = sign_a ^ sign_b;

    if (exp_a == 0xFF) {
        if (sig_a)
            return sfloat_propagate_nan(state, a, b);
        if (exp_b == 0xFF) {
            if (sig_b)
                return sfloat_propagate_nan(state, a, b);
            SFLOAT_RAISE(state, SFLOAT_INVALID);
            return SFLOAT_NAN;
        }
        return SFLOAT_PACK(sign_z, 0xFF, 0);
    }
    if (exp_b == 0xFF)
        return (sig_b) ? sfloat_propagate_nan(state, a, b) : SFLOAT_PACK(sign_z, 0, 0);
    if (exp_b == 0) {
        if (sig_b == 0) {
            if ((exp_a | sig_a) == 0) {
                SFLOAT_RAISE(state, SFLOAT_INVALID);
                return SFLOAT_NAN;
            }
            SFLOAT_RAISE(state, SFLOAT_DIVBYZERO);
            return SFLOAT_PACK(sign_z, 0xFF, 0);
        }
        SFLOAT_SUBNORMALIZE(sig_b, &exp_b, &sig_b);
    }
    if (exp_a == 0) {
        if (sig_a == 0)
            return SFLOAT_PACK(sign_z, 0, 0);
        SFLOAT_SUBNORMALIZE(sig_a, &exp_a, &sig_a);
    }
    exp_z = exp_a - exp_b + 0x7D;
    sig_a = (sig_a | 0x00800000) << 7;
    sig_b = (sig_b | 0x00800000) << 8;
    if (sig_b <= (sig_a + sig_a)) {
        sig_a >>= 1;
        ++exp_z;
    }
    sig_z = (((uint64_t)sig_a) << 32) / sig_b;
    if ((sig_z & 0x3F) == 0)
        sig_z |= ((uint64_t)sig_b * sig_z != ((uint64_t)sig_a) << 32);
    return SFLOAT_PACK_round(state, sign_z, exp_z, sig_z);
}

/*
 * There is two stages to constant folding in GMQCC: there is the parse
 * stage constant folding, where, witht he help of the AST, operator
 * usages can be constant folded. Then there is the constant folding
 * in the IR for things like eliding if statements, can occur.
 *
 * This file is thus, split into two parts.
 */

#define isfloat(X)      (((ast_expression*)(X))->vtype == TYPE_FLOAT)
#define isvector(X)     (((ast_expression*)(X))->vtype == TYPE_VECTOR)
#define isstring(X)     (((ast_expression*)(X))->vtype == TYPE_STRING)
#define isfloats(X,Y)   (isfloat  (X) && isfloat (Y))

/*
 * Implementation of basic vector math for vec3_t, for trivial constant
 * folding.
 *
 * TODO: gcc/clang hinting for autovectorization
 */
static GMQCC_INLINE vec3_t vec3_add(vec3_t a, vec3_t b) {
    vec3_t out;
    out.x = a.x + b.x;
    out.y = a.y + b.y;
    out.z = a.z + b.z;
    return out;
}

static GMQCC_INLINE vec3_t vec3_sub(vec3_t a, vec3_t b) {
    vec3_t out;
    out.x = a.x - b.x;
    out.y = a.y - b.y;
    out.z = a.z - b.z;
    return out;
}

static GMQCC_INLINE vec3_t vec3_neg(vec3_t a) {
    vec3_t out;
    out.x = -a.x;
    out.y = -a.y;
    out.z = -a.z;
    return out;
}

static GMQCC_INLINE vec3_t vec3_or(vec3_t a, vec3_t b) {
    vec3_t out;
    out.x = (qcfloat_t)(((qcint_t)a.x) | ((qcint_t)b.x));
    out.y = (qcfloat_t)(((qcint_t)a.y) | ((qcint_t)b.y));
    out.z = (qcfloat_t)(((qcint_t)a.z) | ((qcint_t)b.z));
    return out;
}

static GMQCC_INLINE vec3_t vec3_orvf(vec3_t a, qcfloat_t b) {
    vec3_t out;
    out.x = (qcfloat_t)(((qcint_t)a.x) | ((qcint_t)b));
    out.y = (qcfloat_t)(((qcint_t)a.y) | ((qcint_t)b));
    out.z = (qcfloat_t)(((qcint_t)a.z) | ((qcint_t)b));
    return out;
}

static GMQCC_INLINE vec3_t vec3_and(vec3_t a, vec3_t b) {
    vec3_t out;
    out.x = (qcfloat_t)(((qcint_t)a.x) & ((qcint_t)b.x));
    out.y = (qcfloat_t)(((qcint_t)a.y) & ((qcint_t)b.y));
    out.z = (qcfloat_t)(((qcint_t)a.z) & ((qcint_t)b.z));
    return out;
}

static GMQCC_INLINE vec3_t vec3_andvf(vec3_t a, qcfloat_t b) {
    vec3_t out;
    out.x = (qcfloat_t)(((qcint_t)a.x) & ((qcint_t)b));
    out.y = (qcfloat_t)(((qcint_t)a.y) & ((qcint_t)b));
    out.z = (qcfloat_t)(((qcint_t)a.z) & ((qcint_t)b));
    return out;
}

static GMQCC_INLINE vec3_t vec3_xor(vec3_t a, vec3_t b) {
    vec3_t out;
    out.x = (qcfloat_t)(((qcint_t)a.x) ^ ((qcint_t)b.x));
    out.y = (qcfloat_t)(((qcint_t)a.y) ^ ((qcint_t)b.y));
    out.z = (qcfloat_t)(((qcint_t)a.z) ^ ((qcint_t)b.z));
    return out;
}

static GMQCC_INLINE vec3_t vec3_xorvf(vec3_t a, qcfloat_t b) {
    vec3_t out;
    out.x = (qcfloat_t)(((qcint_t)a.x) ^ ((qcint_t)b));
    out.y = (qcfloat_t)(((qcint_t)a.y) ^ ((qcint_t)b));
    out.z = (qcfloat_t)(((qcint_t)a.z) ^ ((qcint_t)b));
    return out;
}

static GMQCC_INLINE vec3_t vec3_not(vec3_t a) {
    vec3_t out;
    out.x = -1-a.x;
    out.y = -1-a.y;
    out.z = -1-a.z;
    return out;
}

static GMQCC_INLINE qcfloat_t vec3_mulvv(vec3_t a, vec3_t b) {
    return (a.x * b.x + a.y * b.y + a.z * b.z);
}

static GMQCC_INLINE vec3_t vec3_mulvf(vec3_t a, qcfloat_t b) {
    vec3_t out;
    out.x = a.x * b;
    out.y = a.y * b;
    out.z = a.z * b;
    return out;
}

static GMQCC_INLINE bool vec3_cmp(vec3_t a, vec3_t b) {
    return a.x == b.x &&
           a.y == b.y &&
           a.z == b.z;
}

static GMQCC_INLINE vec3_t vec3_create(float x, float y, float z) {
    vec3_t out;
    out.x = x;
    out.y = y;
    out.z = z;
    return out;
}

static GMQCC_INLINE qcfloat_t vec3_notf(vec3_t a) {
    return (!a.x && !a.y && !a.z);
}

static GMQCC_INLINE bool vec3_pbool(vec3_t a) {
    return (a.x || a.y || a.z);
}

static GMQCC_INLINE vec3_t vec3_cross(vec3_t a, vec3_t b) {
    vec3_t out;
    out.x = a.y * b.z - a.z * b.y;
    out.y = a.z * b.x - a.x * b.z;
    out.z = a.x * b.y - a.y * b.x;
    return out;
}

static lex_ctx_t fold_ctx(fold_t *fold) {
    lex_ctx_t ctx;
    if (fold->parser->lex)
        return parser_ctx(fold->parser);

    memset(&ctx, 0, sizeof(ctx));
    return ctx;
}

static GMQCC_INLINE bool fold_immediate_true(fold_t *fold, ast_value *v) {
    switch (v->expression.vtype) {
        case TYPE_FLOAT:
            return !!v->constval.vfloat;
        case TYPE_INTEGER:
            return !!v->constval.vint;
        case TYPE_VECTOR:
            if (OPTS_FLAG(CORRECT_LOGIC))
                return vec3_pbool(v->constval.vvec);
            return !!(v->constval.vvec.x);
        case TYPE_STRING:
            if (!v->constval.vstring)
                return false;
            if (OPTS_FLAG(TRUE_EMPTY_STRINGS))
                return true;
            return !!v->constval.vstring[0];
        default:
            compile_error(fold_ctx(fold), "internal error: fold_immediate_true on invalid type");
            break;
    }
    return !!v->constval.vfunc;
}

/* Handy macros to determine if an ast_value can be constant folded. */
#define fold_can_1(X)  \
    (ast_istype(((ast_expression*)(X)), ast_value) && (X)->hasvalue && ((X)->cvq == CV_CONST) && \
                ((ast_expression*)(X))->vtype != TYPE_FUNCTION)

#define fold_can_2(X, Y) (fold_can_1(X) && fold_can_1(Y))

#define fold_immvalue_float(E)  ((E)->constval.vfloat)
#define fold_immvalue_vector(E) ((E)->constval.vvec)
#define fold_immvalue_string(E) ((E)->constval.vstring)

fold_t *fold_init(parser_t *parser) {
    fold_t *fold                 = (fold_t*)mem_a(sizeof(fold_t));
    fold->parser                 = parser;
    fold->imm_float              = NULL;
    fold->imm_vector             = NULL;
    fold->imm_string             = NULL;
    fold->imm_string_untranslate = util_htnew(FOLD_STRING_UNTRANSLATE_HTSIZE);
    fold->imm_string_dotranslate = util_htnew(FOLD_STRING_DOTRANSLATE_HTSIZE);

    /*
     * prime the tables with common constant values at constant
     * locations.
     */
    (void)fold_constgen_float (fold,  0.0f, false);
    (void)fold_constgen_float (fold,  1.0f, false);
    (void)fold_constgen_float (fold, -1.0f, false);
    (void)fold_constgen_float (fold,  2.0f, false);

    (void)fold_constgen_vector(fold, vec3_create(0.0f, 0.0f, 0.0f));
    (void)fold_constgen_vector(fold, vec3_create(-1.0f, -1.0f, -1.0f));

    return fold;
}

bool fold_generate(fold_t *fold, ir_builder *ir) {
    /* generate globals for immediate folded values */
    size_t     i;
    ast_value *cur;

    for (i = 0; i < vec_size(fold->imm_float);   ++i)
        if (!ast_global_codegen ((cur = fold->imm_float[i]), ir, false)) goto err;
    for (i = 0; i < vec_size(fold->imm_vector);  ++i)
        if (!ast_global_codegen((cur = fold->imm_vector[i]), ir, false)) goto err;
    for (i = 0; i < vec_size(fold->imm_string);  ++i)
        if (!ast_global_codegen((cur = fold->imm_string[i]), ir, false)) goto err;

    return true;

err:
    con_out("failed to generate global %s\n", cur->name);
    ir_builder_delete(ir);
    return false;
}

void fold_cleanup(fold_t *fold) {
    size_t i;

    for (i = 0; i < vec_size(fold->imm_float);  ++i) ast_delete(fold->imm_float[i]);
    for (i = 0; i < vec_size(fold->imm_vector); ++i) ast_delete(fold->imm_vector[i]);
    for (i = 0; i < vec_size(fold->imm_string); ++i) ast_delete(fold->imm_string[i]);

    vec_free(fold->imm_float);
    vec_free(fold->imm_vector);
    vec_free(fold->imm_string);

    util_htdel(fold->imm_string_untranslate);
    util_htdel(fold->imm_string_dotranslate);

    mem_d(fold);
}

ast_expression *fold_constgen_float(fold_t *fold, qcfloat_t value, bool inexact) {
    ast_value  *out = NULL;
    size_t      i;

    for (i = 0; i < vec_size(fold->imm_float); i++) {
        if (!memcmp(&fold->imm_float[i]->constval.vfloat, &value, sizeof(qcfloat_t)))
            return (ast_expression*)fold->imm_float[i];
    }

    out                  = ast_value_new(fold_ctx(fold), "#IMMEDIATE", TYPE_FLOAT);
    out->cvq             = CV_CONST;
    out->hasvalue        = true;
    out->inexact         = inexact;
    out->constval.vfloat = value;

    vec_push(fold->imm_float, out);

    return (ast_expression*)out;
}

ast_expression *fold_constgen_vector(fold_t *fold, vec3_t value) {
    ast_value *out;
    size_t     i;

    for (i = 0; i < vec_size(fold->imm_vector); i++) {
        if (vec3_cmp(fold->imm_vector[i]->constval.vvec, value))
            return (ast_expression*)fold->imm_vector[i];
    }

    out                = ast_value_new(fold_ctx(fold), "#IMMEDIATE", TYPE_VECTOR);
    out->cvq           = CV_CONST;
    out->hasvalue      = true;
    out->constval.vvec = value;

    vec_push(fold->imm_vector, out);

    return (ast_expression*)out;
}

ast_expression *fold_constgen_string(fold_t *fold, const char *str, bool translate) {
    hash_table_t *table = (translate) ? fold->imm_string_untranslate : fold->imm_string_dotranslate;
    ast_value    *out   = NULL;
    size_t        hash  = util_hthash(table, str);

    if ((out = (ast_value*)util_htgeth(table, str, hash)))
        return (ast_expression*)out;

    if (translate) {
        char name[32];
        util_snprintf(name, sizeof(name), "dotranslate_%lu", (unsigned long)(fold->parser->translated++));
        out                    = ast_value_new(parser_ctx(fold->parser), name, TYPE_STRING);
        out->expression.flags |= AST_FLAG_INCLUDE_DEF; /* def needs to be included for translatables */
    } else
        out                    = ast_value_new(fold_ctx(fold), "#IMMEDIATE", TYPE_STRING);

    out->cvq              = CV_CONST;
    out->hasvalue         = true;
    out->isimm            = true;
    out->constval.vstring = parser_strdup(str);

    vec_push(fold->imm_string, out);
    util_htseth(table, str, hash, out);

    return (ast_expression*)out;
}


static GMQCC_INLINE ast_expression *fold_op_mul_vec(fold_t *fold, vec3_t vec, ast_value *sel, const char *set) {
    /*
     * vector-component constant folding works by matching the component sets
     * to eliminate expensive operations on whole-vectors (3 components at runtime).
     * to achive this effect in a clean manner this function generalizes the
     * values through the use of a set paramater, which is used as an indexing method
     * for creating the elided ast binary expression.
     *
     * Consider 'n 0 0' where y, and z need to be tested for 0, and x is
     * used as the value in a binary operation generating an INSTR_MUL instruction,
     * to acomplish the indexing of the correct component value we use set[0], set[1], set[2]
     * as x, y, z, where the values of those operations return 'x', 'y', 'z'. Because
     * of how ASCII works we can easily deliniate:
     * vec.z is the same as set[2]-'x' for when set[2] is 'z', 'z'-'x' results in a
     * literal value of 2, using this 2, we know that taking the address of vec->x (float)
     * and indxing it with this literal will yeild the immediate address of that component
     *
     * Of course more work needs to be done to generate the correct index for the ast_member_new
     * call, which is no problem: set[0]-'x' suffices that job.
     */
    qcfloat_t x = (&vec.x)[set[0]-'x'];
    qcfloat_t y = (&vec.x)[set[1]-'x'];
    qcfloat_t z = (&vec.x)[set[2]-'x'];

    if (!y && !z) {
        ast_expression *out;
        ++opts_optimizationcount[OPTIM_VECTOR_COMPONENTS];
        out                        = (ast_expression*)ast_member_new(fold_ctx(fold), (ast_expression*)sel, set[0]-'x', NULL);
        out->node.keep             = false;
        ((ast_member*)out)->rvalue = true;
        if (x != -1.0f)
            return (ast_expression*)ast_binary_new(fold_ctx(fold), INSTR_MUL_F, fold_constgen_float(fold, x, false), out);
    }
    return NULL;
}


static GMQCC_INLINE ast_expression *fold_op_neg(fold_t *fold, ast_value *a) {
    if (isfloat(a)) {
        if (fold_can_1(a))
            return fold_constgen_float(fold, -fold_immvalue_float(a), false);
    } else if (isvector(a)) {
        if (fold_can_1(a))
            return fold_constgen_vector(fold, vec3_neg(fold_immvalue_vector(a)));
    }
    return NULL;
}

static GMQCC_INLINE ast_expression *fold_op_not(fold_t *fold, ast_value *a) {
    if (isfloat(a)) {
        if (fold_can_1(a))
            return fold_constgen_float(fold, !fold_immvalue_float(a), false);
    } else if (isvector(a)) {
        if (fold_can_1(a))
            return fold_constgen_float(fold, vec3_notf(fold_immvalue_vector(a)), false);
    } else if (isstring(a)) {
        if (fold_can_1(a)) {
            if (OPTS_FLAG(TRUE_EMPTY_STRINGS))
                return fold_constgen_float(fold, !fold_immvalue_string(a), false);
            else
                return fold_constgen_float(fold, !fold_immvalue_string(a) || !*fold_immvalue_string(a), false);
        }
    }
    return NULL;
}

static bool fold_check_except_float(sfloat_t (*callback)(sfloat_state_t *, sfloat_t, sfloat_t),
                                    fold_t    *fold,
                                    ast_value *a,
                                    ast_value *b)
{
    sfloat_state_t s;
    sfloat_cast_t ca;
    sfloat_cast_t cb;

    s.roundingmode   = SFLOAT_ROUND_NEAREST_EVEN;
    s.tiny           = SFLOAT_TBEFORE;
    s.exceptionflags = 0;
    ca.f             = fold_immvalue_float(a);
    cb.f             = fold_immvalue_float(b);

    callback(&s, ca.s, cb.s);
    if (s.exceptionflags == 0)
        return false;

    if (s.exceptionflags & SFLOAT_DIVBYZERO)
        compile_error(fold_ctx(fold), "division by zero");
#if 0
    /*
     * To be enabled once softfloat implementations for stuff like sqrt()
     * exist
     */
    if (s.exceptionflags & SFLOAT_INVALID)
        compile_error(fold_ctx(fold), "invalid argument");
#endif

    if (s.exceptionflags & SFLOAT_OVERFLOW)
        compile_error(fold_ctx(fold), "arithmetic overflow");
    if (s.exceptionflags & SFLOAT_UNDERFLOW)
        compile_error(fold_ctx(fold), "arithmetic underflow");

    return s.exceptionflags == SFLOAT_INEXACT;
}

static bool fold_check_inexact_float(fold_t *fold, ast_value *a, ast_value *b) {
    lex_ctx_t ctx = fold_ctx(fold);
    if (!a->inexact && !b->inexact)
        return false;
    return compile_warning(ctx, WARN_INEXACT_COMPARES, "inexact value in comparison");
}

static GMQCC_INLINE ast_expression *fold_op_add(fold_t *fold, ast_value *a, ast_value *b) {
    if (isfloat(a)) {
        if (fold_can_2(a, b)) {
            bool inexact = fold_check_except_float(&sfloat_add, fold, a, b);
            return fold_constgen_float(fold, fold_immvalue_float(a) + fold_immvalue_float(b), inexact);
        }
    } else if (isvector(a)) {
        if (fold_can_2(a, b))
            return fold_constgen_vector(fold, vec3_add(fold_immvalue_vector(a), fold_immvalue_vector(b)));
    }
    return NULL;
}

static GMQCC_INLINE ast_expression *fold_op_sub(fold_t *fold, ast_value *a, ast_value *b) {
    if (isfloat(a)) {
        if (fold_can_2(a, b)) {
            bool inexact = fold_check_except_float(&sfloat_sub, fold, a, b);
            return fold_constgen_float(fold, fold_immvalue_float(a) - fold_immvalue_float(b), inexact);
        }
    } else if (isvector(a)) {
        if (fold_can_2(a, b))
            return fold_constgen_vector(fold, vec3_sub(fold_immvalue_vector(a), fold_immvalue_vector(b)));
    }
    return NULL;
}

static GMQCC_INLINE ast_expression *fold_op_mul(fold_t *fold, ast_value *a, ast_value *b) {
    if (isfloat(a)) {
        if (isvector(b)) {
            if (fold_can_2(a, b))
                return fold_constgen_vector(fold, vec3_mulvf(fold_immvalue_vector(b), fold_immvalue_float(a)));
        } else {
            if (fold_can_2(a, b)) {
                bool inexact = fold_check_except_float(&sfloat_mul, fold, a, b);
                return fold_constgen_float(fold, fold_immvalue_float(a) * fold_immvalue_float(b), inexact);
            }
        }
    } else if (isvector(a)) {
        if (isfloat(b)) {
            if (fold_can_2(a, b))
                return fold_constgen_vector(fold, vec3_mulvf(fold_immvalue_vector(a), fold_immvalue_float(b)));
        } else {
            if (fold_can_2(a, b)) {
                return fold_constgen_float(fold, vec3_mulvv(fold_immvalue_vector(a), fold_immvalue_vector(b)), false);
            } else if (OPTS_OPTIMIZATION(OPTIM_VECTOR_COMPONENTS) && fold_can_1(a)) {
                ast_expression *out;
                if ((out = fold_op_mul_vec(fold, fold_immvalue_vector(a), b, "xyz"))) return out;
                if ((out = fold_op_mul_vec(fold, fold_immvalue_vector(a), b, "yxz"))) return out;
                if ((out = fold_op_mul_vec(fold, fold_immvalue_vector(a), b, "zxy"))) return out;
            } else if (OPTS_OPTIMIZATION(OPTIM_VECTOR_COMPONENTS) && fold_can_1(b)) {
                ast_expression *out;
                if ((out = fold_op_mul_vec(fold, fold_immvalue_vector(b), a, "xyz"))) return out;
                if ((out = fold_op_mul_vec(fold, fold_immvalue_vector(b), a, "yxz"))) return out;
                if ((out = fold_op_mul_vec(fold, fold_immvalue_vector(b), a, "zxy"))) return out;
            }
        }
    }
    return NULL;
}

static GMQCC_INLINE ast_expression *fold_op_div(fold_t *fold, ast_value *a, ast_value *b) {
    if (isfloat(a)) {
        if (fold_can_2(a, b)) {
            bool inexact = fold_check_except_float(&sfloat_div, fold, a, b);
            return fold_constgen_float(fold, fold_immvalue_float(a) / fold_immvalue_float(b), inexact);
        } else if (fold_can_1(b)) {
            return (ast_expression*)ast_binary_new(
                fold_ctx(fold),
                INSTR_MUL_F,
                (ast_expression*)a,
                fold_constgen_float(fold, 1.0f / fold_immvalue_float(b), false)
            );
        }
    } else if (isvector(a)) {
        if (fold_can_2(a, b)) {
            return fold_constgen_vector(fold, vec3_mulvf(fold_immvalue_vector(a), 1.0f / fold_immvalue_float(b)));
        } else {
            return (ast_expression*)ast_binary_new(
                fold_ctx(fold),
                INSTR_MUL_VF,
                (ast_expression*)a,
                (fold_can_1(b))
                    ? (ast_expression*)fold_constgen_float(fold, 1.0f / fold_immvalue_float(b), false)
                    : (ast_expression*)ast_binary_new(
                                            fold_ctx(fold),
                                            INSTR_DIV_F,
                                            (ast_expression*)fold->imm_float[1],
                                            (ast_expression*)b
                    )
            );
        }
    }
    return NULL;
}

static GMQCC_INLINE ast_expression *fold_op_mod(fold_t *fold, ast_value *a, ast_value *b) {
    return (fold_can_2(a, b))
                ? fold_constgen_float(fold, fmod(fold_immvalue_float(a), fold_immvalue_float(b)), false)
                : NULL;
}

static GMQCC_INLINE ast_expression *fold_op_bor(fold_t *fold, ast_value *a, ast_value *b) {
    if (isfloat(a)) {
        if (fold_can_2(a, b))
            return fold_constgen_float(fold, (qcfloat_t)(((qcint_t)fold_immvalue_float(a)) | ((qcint_t)fold_immvalue_float(b))), false);
    } else {
        if (isvector(b)) {
            if (fold_can_2(a, b))
                return fold_constgen_vector(fold, vec3_or(fold_immvalue_vector(a), fold_immvalue_vector(b)));
        } else {
            if (fold_can_2(a, b))
                return fold_constgen_vector(fold, vec3_orvf(fold_immvalue_vector(a), fold_immvalue_float(b)));
        }
    }
    return NULL;
}

static GMQCC_INLINE ast_expression *fold_op_band(fold_t *fold, ast_value *a, ast_value *b) {
    if (isfloat(a)) {
        if (fold_can_2(a, b))
            return fold_constgen_float(fold, (qcfloat_t)(((qcint_t)fold_immvalue_float(a)) & ((qcint_t)fold_immvalue_float(b))), false);
    } else {
        if (isvector(b)) {
            if (fold_can_2(a, b))
                return fold_constgen_vector(fold, vec3_and(fold_immvalue_vector(a), fold_immvalue_vector(b)));
        } else {
            if (fold_can_2(a, b))
                return fold_constgen_vector(fold, vec3_andvf(fold_immvalue_vector(a), fold_immvalue_float(b)));
        }
    }
    return NULL;
}

static GMQCC_INLINE ast_expression *fold_op_xor(fold_t *fold, ast_value *a, ast_value *b) {
    if (isfloat(a)) {
        if (fold_can_2(a, b))
            return fold_constgen_float(fold, (qcfloat_t)(((qcint_t)fold_immvalue_float(a)) ^ ((qcint_t)fold_immvalue_float(b))), false);
    } else {
        if (fold_can_2(a, b)) {
            if (isvector(b))
                return fold_constgen_vector(fold, vec3_xor(fold_immvalue_vector(a), fold_immvalue_vector(b)));
            else
                return fold_constgen_vector(fold, vec3_xorvf(fold_immvalue_vector(a), fold_immvalue_float(b)));
        }
    }
    return NULL;
}

static GMQCC_INLINE ast_expression *fold_op_lshift(fold_t *fold, ast_value *a, ast_value *b) {
    if (fold_can_2(a, b) && isfloats(a, b))
        return fold_constgen_float(fold, (qcfloat_t)floorf(fold_immvalue_float(a) * powf(2.0f, fold_immvalue_float(b))), false);
    return NULL;
}

static GMQCC_INLINE ast_expression *fold_op_rshift(fold_t *fold, ast_value *a, ast_value *b) {
    if (fold_can_2(a, b) && isfloats(a, b))
        return fold_constgen_float(fold, (qcfloat_t)floorf(fold_immvalue_float(a) / powf(2.0f, fold_immvalue_float(b))), false);
    return NULL;
}

static GMQCC_INLINE ast_expression *fold_op_andor(fold_t *fold, ast_value *a, ast_value *b, float expr) {
    if (fold_can_2(a, b)) {
        if (OPTS_FLAG(PERL_LOGIC)) {
            if (expr)
                return (fold_immediate_true(fold, a)) ? (ast_expression*)a : (ast_expression*)b;
            else
                return (fold_immediate_true(fold, a)) ? (ast_expression*)b : (ast_expression*)a;
        } else {
            return fold_constgen_float (
                fold,
                ((expr) ? (fold_immediate_true(fold, a) || fold_immediate_true(fold, b))
                        : (fold_immediate_true(fold, a) && fold_immediate_true(fold, b)))
                            ? 1
                            : 0,
                false
            );
        }
    }
    return NULL;
}

static GMQCC_INLINE ast_expression *fold_op_tern(fold_t *fold, ast_value *a, ast_value *b, ast_value *c) {
    if (fold_can_1(a)) {
        return fold_immediate_true(fold, a)
                    ? (ast_expression*)b
                    : (ast_expression*)c;
    }
    return NULL;
}

static GMQCC_INLINE ast_expression *fold_op_exp(fold_t *fold, ast_value *a, ast_value *b) {
    if (fold_can_2(a, b))
        return fold_constgen_float(fold, (qcfloat_t)powf(fold_immvalue_float(a), fold_immvalue_float(b)), false);
    return NULL;
}

static GMQCC_INLINE ast_expression *fold_op_lteqgt(fold_t *fold, ast_value *a, ast_value *b) {
    if (fold_can_2(a,b)) {
        fold_check_inexact_float(fold, a, b);
        if (fold_immvalue_float(a) <  fold_immvalue_float(b)) return (ast_expression*)fold->imm_float[2];
        if (fold_immvalue_float(a) == fold_immvalue_float(b)) return (ast_expression*)fold->imm_float[0];
        if (fold_immvalue_float(a) >  fold_immvalue_float(b)) return (ast_expression*)fold->imm_float[1];
    }
    return NULL;
}

static GMQCC_INLINE ast_expression *fold_op_ltgt(fold_t *fold, ast_value *a, ast_value *b, bool lt) {
    if (fold_can_2(a, b)) {
        fold_check_inexact_float(fold, a, b);
        return (lt) ? (ast_expression*)fold->imm_float[!!(fold_immvalue_float(a) < fold_immvalue_float(b))]
                    : (ast_expression*)fold->imm_float[!!(fold_immvalue_float(a) > fold_immvalue_float(b))];
    }
    return NULL;
}

static GMQCC_INLINE ast_expression *fold_op_cmp(fold_t *fold, ast_value *a, ast_value *b, bool ne) {
    if (fold_can_2(a, b)) {
        if (isfloat(a) && isfloat(b)) {
            float la = fold_immvalue_float(a);
            float lb = fold_immvalue_float(b);
            fold_check_inexact_float(fold, a, b);
            return (ast_expression*)fold->imm_float[!(ne ? la == lb : la != lb)];
        } if (isvector(a) && isvector(b)) {
            vec3_t la = fold_immvalue_vector(a);
            vec3_t lb = fold_immvalue_vector(b);
            return (ast_expression*)fold->imm_float[!(ne ? vec3_cmp(la, lb) : !vec3_cmp(la, lb))];
        }
    }
    return NULL;
}

static GMQCC_INLINE ast_expression *fold_op_bnot(fold_t *fold, ast_value *a) {
    if (isfloat(a)) {
        if (fold_can_1(a))
            return fold_constgen_float(fold, -1-fold_immvalue_float(a), false);
    } else {
        if (isvector(a)) {
            if (fold_can_1(a))
                return fold_constgen_vector(fold, vec3_not(fold_immvalue_vector(a)));
        }
    }
    return NULL;
}

static GMQCC_INLINE ast_expression *fold_op_cross(fold_t *fold, ast_value *a, ast_value *b) {
    if (fold_can_2(a, b))
        return fold_constgen_vector(fold, vec3_cross(fold_immvalue_vector(a), fold_immvalue_vector(b)));
    return NULL;
}

ast_expression *fold_op(fold_t *fold, const oper_info *info, ast_expression **opexprs) {
    ast_value      *a = (ast_value*)opexprs[0];
    ast_value      *b = (ast_value*)opexprs[1];
    ast_value      *c = (ast_value*)opexprs[2];
    ast_expression *e = NULL;

    /* can a fold operation be applied to this operator usage? */
    if (!info->folds)
        return NULL;

    switch(info->operands) {
        case 3: if(!c) return NULL;
        case 2: if(!b) return NULL;
        case 1:
        if(!a) {
            compile_error(fold_ctx(fold), "internal error: fold_op no operands to fold\n");
            return NULL;
        }
    }

    /*
     * we could use a boolean and default case but ironically gcc produces
     * invalid broken assembly from that operation. clang/tcc get it right,
     * but interestingly ignore compiling this to a jump-table when I do that,
     * this happens to be the most efficent method, since you have per-level
     * granularity on the pointer check happening only for the case you check
     * it in. Opposed to the default method which would involve a boolean and
     * pointer check after wards.
     */
    #define fold_op_case(ARGS, ARGS_OPID, OP, ARGS_FOLD)    \
        case opid##ARGS ARGS_OPID:                          \
            if ((e = fold_op_##OP ARGS_FOLD)) {             \
                ++opts_optimizationcount[OPTIM_CONST_FOLD]; \
            }                                               \
            return e

    switch(info->id) {
        fold_op_case(2, ('-', 'P'),    neg,    (fold, a));
        fold_op_case(2, ('!', 'P'),    not,    (fold, a));
        fold_op_case(1, ('+'),         add,    (fold, a, b));
        fold_op_case(1, ('-'),         sub,    (fold, a, b));
        fold_op_case(1, ('*'),         mul,    (fold, a, b));
        fold_op_case(1, ('/'),         div,    (fold, a, b));
        fold_op_case(1, ('%'),         mod,    (fold, a, b));
        fold_op_case(1, ('|'),         bor,    (fold, a, b));
        fold_op_case(1, ('&'),         band,   (fold, a, b));
        fold_op_case(1, ('^'),         xor,    (fold, a, b));
        fold_op_case(1, ('<'),         ltgt,   (fold, a, b, true));
        fold_op_case(1, ('>'),         ltgt,   (fold, a, b, false));
        fold_op_case(2, ('<', '<'),    lshift, (fold, a, b));
        fold_op_case(2, ('>', '>'),    rshift, (fold, a, b));
        fold_op_case(2, ('|', '|'),    andor,  (fold, a, b, true));
        fold_op_case(2, ('&', '&'),    andor,  (fold, a, b, false));
        fold_op_case(2, ('?', ':'),    tern,   (fold, a, b, c));
        fold_op_case(2, ('*', '*'),    exp,    (fold, a, b));
        fold_op_case(3, ('<','=','>'), lteqgt, (fold, a, b));
        fold_op_case(2, ('!', '='),    cmp,    (fold, a, b, true));
        fold_op_case(2, ('=', '='),    cmp,    (fold, a, b, false));
        fold_op_case(2, ('~', 'P'),    bnot,   (fold, a));
        fold_op_case(2, ('>', '<'),    cross,  (fold, a, b));
    }
    #undef fold_op_case
    compile_error(fold_ctx(fold), "internal error: attempted to constant-fold for unsupported operator");
    return NULL;
}

/*
 * Constant folding for compiler intrinsics, simaler approach to operator
 * folding, primarly: individual functions for each intrinsics to fold,
 * and a generic selection function.
 */
static GMQCC_INLINE ast_expression *fold_intrin_isfinite(fold_t *fold, ast_value *a) {
    return fold_constgen_float(fold, isfinite(fold_immvalue_float(a)), false);
}
static GMQCC_INLINE ast_expression *fold_intrin_isinf(fold_t *fold, ast_value *a) {
    return fold_constgen_float(fold, isinf(fold_immvalue_float(a)), false);
}
static GMQCC_INLINE ast_expression *fold_intrin_isnan(fold_t *fold, ast_value *a) {
    return fold_constgen_float(fold, isnan(fold_immvalue_float(a)), false);
}
static GMQCC_INLINE ast_expression *fold_intrin_isnormal(fold_t *fold, ast_value *a) {
    return fold_constgen_float(fold, isnormal(fold_immvalue_float(a)), false);
}
static GMQCC_INLINE ast_expression *fold_intrin_signbit(fold_t *fold, ast_value *a) {
    return fold_constgen_float(fold, signbit(fold_immvalue_float(a)), false);
}
static GMQCC_INLINE ast_expression *fold_intirn_acosh(fold_t *fold, ast_value *a) {
    return fold_constgen_float(fold, acoshf(fold_immvalue_float(a)), false);
}
static GMQCC_INLINE ast_expression *fold_intrin_asinh(fold_t *fold, ast_value *a) {
    return fold_constgen_float(fold, asinhf(fold_immvalue_float(a)), false);
}
static GMQCC_INLINE ast_expression *fold_intrin_atanh(fold_t *fold, ast_value *a) {
    return fold_constgen_float(fold, (float)atanh(fold_immvalue_float(a)), false);
}
static GMQCC_INLINE ast_expression *fold_intrin_exp(fold_t *fold, ast_value *a) {
    return fold_constgen_float(fold, expf(fold_immvalue_float(a)), false);
}
static GMQCC_INLINE ast_expression *fold_intrin_exp2(fold_t *fold, ast_value *a) {
    return fold_constgen_float(fold, exp2f(fold_immvalue_float(a)), false);
}
static GMQCC_INLINE ast_expression *fold_intrin_expm1(fold_t *fold, ast_value *a) {
    return fold_constgen_float(fold, expm1f(fold_immvalue_float(a)), false);
}
static GMQCC_INLINE ast_expression *fold_intrin_mod(fold_t *fold, ast_value *lhs, ast_value *rhs) {
    return fold_constgen_float(fold, fmodf(fold_immvalue_float(lhs), fold_immvalue_float(rhs)), false);
}
static GMQCC_INLINE ast_expression *fold_intrin_pow(fold_t *fold, ast_value *lhs, ast_value *rhs) {
    return fold_constgen_float(fold, powf(fold_immvalue_float(lhs), fold_immvalue_float(rhs)), false);
}
static GMQCC_INLINE ast_expression *fold_intrin_fabs(fold_t *fold, ast_value *a) {
    return fold_constgen_float(fold, fabsf(fold_immvalue_float(a)), false);
}


ast_expression *fold_intrin(fold_t *fold, const char *intrin, ast_expression **arg) {
    ast_expression *ret = NULL;
    ast_value      *a   = (ast_value*)arg[0];
    ast_value      *b   = (ast_value*)arg[1];

    if (!strcmp(intrin, "isfinite")) ret = fold_intrin_isfinite(fold, a);
    if (!strcmp(intrin, "isinf"))    ret = fold_intrin_isinf(fold, a);
    if (!strcmp(intrin, "isnan"))    ret = fold_intrin_isnan(fold, a);
    if (!strcmp(intrin, "isnormal")) ret = fold_intrin_isnormal(fold, a);
    if (!strcmp(intrin, "signbit"))  ret = fold_intrin_signbit(fold, a);
    if (!strcmp(intrin, "acosh"))    ret = fold_intirn_acosh(fold, a);
    if (!strcmp(intrin, "asinh"))    ret = fold_intrin_asinh(fold, a);
    if (!strcmp(intrin, "atanh"))    ret = fold_intrin_atanh(fold, a);
    if (!strcmp(intrin, "exp"))      ret = fold_intrin_exp(fold, a);
    if (!strcmp(intrin, "exp2"))     ret = fold_intrin_exp2(fold, a);
    if (!strcmp(intrin, "expm1"))    ret = fold_intrin_expm1(fold, a);
    if (!strcmp(intrin, "mod"))      ret = fold_intrin_mod(fold, a, b);
    if (!strcmp(intrin, "pow"))      ret = fold_intrin_pow(fold, a, b);
    if (!strcmp(intrin, "fabs"))     ret = fold_intrin_fabs(fold, a);

    if (ret)
        ++opts_optimizationcount[OPTIM_CONST_FOLD];

    return ret;
}

/*
 * These are all the actual constant folding methods that happen in between
 * the AST/IR stage of the compiler , i.e eliminating branches for const
 * expressions, which is the only supported thing so far. We undefine the
 * testing macros here because an ir_value is differant than an ast_value.
 */
#undef expect
#undef isfloat
#undef isstring
#undef isvector
#undef fold_immvalue_float
#undef fold_immvalue_string
#undef fold_immvalue_vector
#undef fold_can_1
#undef fold_can_2

#define isfloat(X)              ((X)->vtype == TYPE_FLOAT)
/*#define isstring(X)             ((X)->vtype == TYPE_STRING)*/
/*#define isvector(X)             ((X)->vtype == TYPE_VECTOR)*/
#define fold_immvalue_float(X)  ((X)->constval.vfloat)
#define fold_immvalue_vector(X) ((X)->constval.vvec)
/*#define fold_immvalue_string(X) ((X)->constval.vstring)*/
#define fold_can_1(X)           ((X)->hasvalue && (X)->cvq == CV_CONST)
/*#define fold_can_2(X,Y)         (fold_can_1(X) && fold_can_1(Y))*/

static ast_expression *fold_superfluous(ast_expression *left, ast_expression *right, int op) {
    ast_expression *swapped = NULL; /* using this as bool */
    ast_value *load;

    if (!ast_istype(right, ast_value) || !fold_can_1((load = (ast_value*)right))) {
        swapped = left;
        left    = right;
        right   = swapped;
    }

    if (!ast_istype(right, ast_value) || !fold_can_1((load = (ast_value*)right)))
        return NULL;

    switch (op) {
        case INSTR_DIV_F:
            if (swapped)
                return NULL;
        case INSTR_MUL_F:
            if (fold_immvalue_float(load) == 1.0f) {
                ++opts_optimizationcount[OPTIM_PEEPHOLE];
                ast_unref(right);
                return left;
            }
            break;


        case INSTR_SUB_F:
            if (swapped)
                return NULL;
        case INSTR_ADD_F:
            if (fold_immvalue_float(load) == 0.0f) {
                ++opts_optimizationcount[OPTIM_PEEPHOLE];
                ast_unref(right);
                return left;
            }
            break;

        case INSTR_MUL_V:
            if (vec3_cmp(fold_immvalue_vector(load), vec3_create(1, 1, 1))) {
                ++opts_optimizationcount[OPTIM_PEEPHOLE];
                ast_unref(right);
                return left;
            }
            break;

        case INSTR_SUB_V:
            if (swapped)
                return NULL;
        case INSTR_ADD_V:
            if (vec3_cmp(fold_immvalue_vector(load), vec3_create(0, 0, 0))) {
                ++opts_optimizationcount[OPTIM_PEEPHOLE];
                ast_unref(right);
                return left;
            }
            break;
    }

    return NULL;
}

ast_expression *fold_binary(lex_ctx_t ctx, int op, ast_expression *left, ast_expression *right) {
    ast_expression *ret = fold_superfluous(left, right, op);
    if (ret)
        return ret;
    return (ast_expression*)ast_binary_new(ctx, op, left, right);
}

static GMQCC_INLINE int fold_cond(ir_value *condval, ast_function *func, ast_ifthen *branch) {
    if (isfloat(condval) && fold_can_1(condval) && OPTS_OPTIMIZATION(OPTIM_CONST_FOLD_DCE)) {
        ast_expression_codegen *cgen;
        ir_block               *elide;
        ir_value               *dummy;
        bool                    istrue  = (fold_immvalue_float(condval) != 0.0f && branch->on_true);
        bool                    isfalse = (fold_immvalue_float(condval) == 0.0f && branch->on_false);
        ast_expression         *path    = (istrue)  ? branch->on_true  :
                                          (isfalse) ? branch->on_false : NULL;
        if (!path) {
            /*
             * no path to take implies that the evaluation is if(0) and there
             * is no else block. so eliminate all the code.
             */
            ++opts_optimizationcount[OPTIM_CONST_FOLD_DCE];
            return true;
        }

        if (!(elide = ir_function_create_block(ast_ctx(branch), func->ir_func, ast_function_label(func, ((istrue) ? "ontrue" : "onfalse")))))
            return false;
        if (!(*(cgen = path->codegen))((ast_expression*)path, func, false, &dummy))
            return false;
        if (!ir_block_create_jump(func->curblock, ast_ctx(branch), elide))
            return false;
        /*
         * now the branch has been eliminated and the correct block for the constant evaluation
         * is expanded into the current block for the function.
         */
        func->curblock = elide;
        ++opts_optimizationcount[OPTIM_CONST_FOLD_DCE];
        return true;
    }
    return -1; /* nothing done */
}

int fold_cond_ternary(ir_value *condval, ast_function *func, ast_ternary *branch) {
    return fold_cond(condval, func, (ast_ifthen*)branch);
}

int fold_cond_ifthen(ir_value *condval, ast_function *func, ast_ifthen *branch) {
    return fold_cond(condval, func, branch);
}