From 95a50fefa26611633e6d65a7431c7ac554a125c9 Mon Sep 17 00:00:00 2001
From: Bill Currie <bill@taniwha.org>
Date: Sun, 7 Apr 2024 01:10:54 +0900
Subject: [PATCH] [qfcc] Aggressively cancel terms

While it currently doesn't have any effect on generated code, it proved
to be necessary when experimenting with optimizing the operand of extend
expressions (which proved to produce worse code).

Along with some 0 -> nullptr changes.
---
 tools/qfcc/source/expr_algebra.c  |  2 +-
 tools/qfcc/source/expr_optimize.c | 34 +++++++++++++++++++++++++------
 2 files changed, 29 insertions(+), 7 deletions(-)

diff --git a/tools/qfcc/source/expr_algebra.c b/tools/qfcc/source/expr_algebra.c
index 78087aac7..cf6c12b51 100644
--- a/tools/qfcc/source/expr_algebra.c
+++ b/tools/qfcc/source/expr_algebra.c
@@ -135,7 +135,7 @@ const expr_t *
 ext_expr (const expr_t *src, const type_t *type, int extend, bool reverse)
 {
 	if (!src) {
-		return 0;
+		return nullptr;
 	}
 	bool neg = false;
 	if (is_neg (src)) {
diff --git a/tools/qfcc/source/expr_optimize.c b/tools/qfcc/source/expr_optimize.c
index 72560189e..707fcb54a 100644
--- a/tools/qfcc/source/expr_optimize.c
+++ b/tools/qfcc/source/expr_optimize.c
@@ -53,7 +53,7 @@ clean_skips (const expr_t **expr_list)
 			*dst++ = *src;
 		}
 	}
-	*dst = 0;
+	*dst = nullptr;
 }
 
 static const expr_t *
@@ -149,7 +149,7 @@ optimize_cross (const expr_t *expr, const expr_t **adds, const expr_t **subs)
 	for (auto search = adds; *search; search++) {
 		if (*search != &skip) {
 			auto c = traverse_scale (*search);
-			const expr_t *scale = 0;
+			const expr_t *scale = nullptr;
 			bool neg = false;
 			if (is_cross (c)) {
 				if (c->expr.e1 == com) {
@@ -173,7 +173,7 @@ optimize_cross (const expr_t *expr, const expr_t **adds, const expr_t **subs)
 	for (auto search = subs; *search; search++) {
 		if (*search != &skip) {
 			auto c = traverse_scale (*search);
-			const expr_t *scale = 0;
+			const expr_t *scale = nullptr;
 			bool neg = false;
 			if (is_cross (c)) {
 				if (c->expr.e1 == com) {
@@ -282,7 +282,7 @@ optimize_scale (const expr_t *expr, const expr_t **adds, const expr_t **subs)
 		return expr;
 	}
 
-	const expr_t *common = 0;
+	const expr_t *common = nullptr;
 	int count = 0;
 	for (auto f = factors; *f; f++) {
 		if (fac_counts[f - factors] > count
@@ -357,7 +357,7 @@ optimize_mult (const expr_t *expr, const expr_t **adds, const expr_t **subs)
 		return expr;
 	}
 
-	const expr_t *common = 0;
+	const expr_t *common = nullptr;
 	int count = 0;
 	for (auto f = factors; *f; f++) {
 		if (fac_counts[f - factors] > count
@@ -387,7 +387,9 @@ optimize_mult (const expr_t *expr, const expr_t **adds, const expr_t **subs)
 
 	auto type = get_type (expr);
 	auto col = gather_terms (type, com_adds, com_subs);
-	col = optimize_core (col);
+	if (!(col = optimize_core (col))) {
+		return nullptr;
+	}
 
 	auto mult = typed_binary_expr (type, expr->expr.op, col, common);
 	mult = edag_add_expr (mult);
@@ -537,6 +539,25 @@ optimize_adds (const expr_t **expr_list)
 	clean_skips (expr_list);
 }
 
+static void
+cancel_terms (const expr_t **adds, const expr_t **subs)
+{
+	for (auto a = adds; *a; a++) {
+		if (*a == &skip) {
+			continue;
+		}
+		for (auto s = subs; *s; s++) {
+			if (*s == *a) {
+				*a = &skip;
+				*s = &skip;
+				break;
+			}
+		}
+	}
+	clean_skips (adds);
+	clean_skips (subs);
+}
+
 static const expr_t *
 optimize_core (const expr_t *expr)
 {
@@ -553,6 +574,7 @@ optimize_core (const expr_t *expr)
 		if (expr->expr.commutative) {
 			optimize_adds (adds);
 			optimize_adds (subs);
+			cancel_terms (adds, subs);
 		}
 
 		optimize_cross_products (adds, subs);