From f4f805f4c980f5e509447a965b4ef811c0741581 Mon Sep 17 00:00:00 2001
From: Rudolf Polzer <divverent@xonotic.org>
Date: Tue, 27 Aug 2013 09:46:58 +0200
Subject: [PATCH] New options: -ftypeless-stores and -fsort-operands

These flags reduce entropy, but not size, of the generated assembly
code. This helps compressability of the files.

Additionally, -ftypeless-stores might SLIGHTLY improve engine
performance due to less instructions being used (so branch prediction
might work better). Probably cannot be measured though.

Signed-off-by: Rudolf Polzer <divverent@xonotic.org>
---
 code.c            | 76 +++++++++++++++++++++++++++++++++++++++++++++--
 doc/gmqcc.1       |  9 ++++++
 gmqcc.ini.example | 15 ++++++++++
 opts.def          |  2 ++
 4 files changed, 100 insertions(+), 2 deletions(-)

diff --git a/code.c b/code.c
index 9251360..2cf0a85 100644
--- a/code.c
+++ b/code.c
@@ -44,9 +44,81 @@ typedef union {
 #define CODE_HASH_ENTER(ENTRY) ((ENTRY).enter)
 #define CODE_HASH_LEAVE(ENTRY) ((ENTRY).leave)
 
-void code_push_statement(code_t *code, prog_section_statement_t *stmt, lex_ctx_t ctx)
+void code_push_statement(code_t *code, prog_section_statement_t *stmt_in, lex_ctx_t ctx)
 {
-    vec_push(code->statements, *stmt);
+    prog_section_statement_t stmt = *stmt_in;
+
+    if (OPTS_FLAG(TYPELESS_STORES)) {
+        switch (stmt.opcode) {
+            case INSTR_LOAD_S:
+            case INSTR_LOAD_ENT:
+            case INSTR_LOAD_FLD:
+            case INSTR_LOAD_FNC:
+                stmt.opcode = INSTR_LOAD_F;
+                break;
+            case INSTR_STORE_S:
+            case INSTR_STORE_ENT:
+            case INSTR_STORE_FLD:
+            case INSTR_STORE_FNC:
+                stmt.opcode = INSTR_STORE_F;
+                break;
+            case INSTR_STOREP_S:
+            case INSTR_STOREP_ENT:
+            case INSTR_STOREP_FLD:
+            case INSTR_STOREP_FNC:
+                stmt.opcode = INSTR_STOREP_F;
+                break;
+        }
+    }
+
+    if (OPTS_FLAG(SORT_OPERANDS)) {
+        switch (stmt.opcode) {
+#define SINGLE(a) \
+            case INSTR_##a: \
+                if (stmt.o1.u1 < stmt.o2.u1) { \
+                    uint16_t x = stmt.o1.u1; stmt.o1.u1 = stmt.o2.u1; stmt.o2.u1 = x; \
+                } \
+                break
+#define PAIR(a,b) \
+            case INSTR_##a: \
+                if (stmt.o1.u1 < stmt.o2.u1) { \
+                    uint16_t x = stmt.o1.u1; stmt.o1.u1 = stmt.o2.u1; stmt.o2.u1 = x; \
+                    stmt.opcode = INSTR_##b; \
+                } \
+                break; \
+            case INSTR_##b: \
+                if (stmt.o1.u1 < stmt.o2.u1) { \
+                    uint16_t x = stmt.o1.u1; stmt.o1.u1 = stmt.o2.u1; stmt.o2.u1 = x; \
+                    stmt.opcode = INSTR_##a; \
+                } \
+                break
+            PAIR(MUL_VF, MUL_FV);
+            PAIR(LT, GT);
+            PAIR(LE, GE);
+            SINGLE(MUL_F);
+            SINGLE(MUL_V);
+            SINGLE(ADD_F);
+            SINGLE(ADD_V);
+            SINGLE(EQ_F);
+            SINGLE(EQ_V);
+            SINGLE(EQ_S);
+            SINGLE(EQ_E);
+            SINGLE(EQ_FNC);
+            SINGLE(NE_F);
+            SINGLE(NE_V);
+            SINGLE(NE_S);
+            SINGLE(NE_E);
+            SINGLE(NE_FNC);
+            SINGLE(AND);
+            SINGLE(OR);
+            SINGLE(BITAND);
+            SINGLE(BITOR);
+#undef PAIR
+#undef SINGLE
+        }
+    }
+
+    vec_push(code->statements, stmt);
     vec_push(code->linenums,   (int)ctx.line);
     vec_push(code->columnnums, (int)ctx.column);
 }
diff --git a/doc/gmqcc.1 b/doc/gmqcc.1
index dbdae03..f3f6517 100644
--- a/doc/gmqcc.1
+++ b/doc/gmqcc.1
@@ -535,6 +535,15 @@ When passing on varargs to a different functions, this turns some
 static error cases into warnings. Like when the caller's varargs are
 restricted to a different type than the callee's parameter. Or a list
 of unrestricted varargs is passed into restricted varargs.
+.It Fl f Ns Cm typeless-stores
+Always use STORE_F, LOAD_F, STOREP_F when accessing scalar variables.
+This is somewhat incorrect assembly instruction use, but in all engines
+they do exactly the same. This makes disassembly output harder to read,
+breaks decompilers, but causes the output file to be better compressible.
+.It Fl f Ns Cm sort-operands
+In commutative instructions, always put the lower-numbered operand first.
+This shaves off 1 byte of entropy from all these instructions, reducing
+compressed size of the output file.
 .El
 .Sh OPTIMIZATIONS
 .Bl -tag -width Ds
diff --git a/gmqcc.ini.example b/gmqcc.ini.example
index 520fb54..9dbb6fb 100644
--- a/gmqcc.ini.example
+++ b/gmqcc.ini.example
@@ -273,6 +273,21 @@
     UNSAFE_VARARGS = false
 
 
+    #Always use STORE_F, LOAD_F, STOREP_F when accessing scalar variables.
+    #This is somewhat incorrect assembly instruction use, but in all engines
+    #they do exactly the same. This makes disassembly output harder to read,
+    #breaks decompilers, but causes the output file to be better compressible.
+
+    TYPELESS_STORES = false
+
+
+    #In commutative instructions, always put the lower-numbered operand first.
+    #This shaves off 1 byte of entropy from all these instructions, reducing
+    #compressed size of the output file.
+
+    SORT_OPERANDS = false
+
+
 
 [warnings]
     #Generate a warning about variables which are declared but never
diff --git a/opts.def b/opts.def
index ef249a3..977272a 100644
--- a/opts.def
+++ b/opts.def
@@ -53,6 +53,8 @@
     GMQCC_DEFINE_FLAG(EXPRESSIONS_FOR_BUILTINS)
     GMQCC_DEFINE_FLAG(RETURN_ASSIGNMENTS)
     GMQCC_DEFINE_FLAG(UNSAFE_VARARGS)
+    GMQCC_DEFINE_FLAG(TYPELESS_STORES)
+    GMQCC_DEFINE_FLAG(SORT_OPERANDS)
 #endif
 
 /* warning flags */