From f978b666620bf01c3403c970906d7ef77912e877 Mon Sep 17 00:00:00 2001
From: Mid <>
Date: Wed, 15 Oct 2025 14:10:42 +0300
Subject: [PATCH] Conditionally save volatile regs

---
 src/ast/usedef.c |  2 ++
 src/x86/cg.c     | 49 ++++++++++++++++++++++++++++++++++++------------
 2 files changed, 39 insertions(+), 12 deletions(-)

diff --git a/src/ast/usedef.c b/src/ast/usedef.c
index 76cae9b..13bb464 100644
--- a/src/ast/usedef.c
+++ b/src/ast/usedef.c
@@ -204,6 +204,8 @@ void ast_usedef_reset(AST *chu) {
 			for(size_t sii = 0; sii < chu->chunk.varCount; sii++) {
 				ScopeItem *si = chu->chunk.vars[sii];
 				
+				assert(si->data.var.declaration != NULL && "All local vars must have defined declaration location");
+				
 				if(ast_stmt_is_after(chu, si->data.var.liveRangeEnd, s) == 0 && ast_stmt_is_after(chu, target, si->data.var.liveRangeEnd) == 0 && ast_stmt_is_after(chu, si->data.var.declaration, target) == 0) {
 					
 					si->data.var.liveRangeEnd = s;
diff --git a/src/x86/cg.c b/src/x86/cg.c
index 2c260a0..96b6022 100644
--- a/src/x86/cg.c
+++ b/src/x86/cg.c
@@ -260,6 +260,27 @@ static int lr_empty(ScopeItem *a) {
 	return !a->data.var.liveRangeStart;
 }
 
+static bool is_resource_in_use_right_now_at_this_current_point_in_time_and_also_not_created_right_now(AST *tlc, AST *statement, size_t resource) {
+	for(size_t vi = 0; vi < tlc->chunk.varCount; vi++) {
+		ScopeItem *si = tlc->chunk.vars[vi];
+		if((REG_CLASSES[si->data.var.registerClass].rs[si->data.var.color] & resource) == 0) {
+			continue;
+		}
+		if(ast_stmt_is_after(tlc, statement, si->data.var.liveRangeEnd) == 1 || statement == si->data.var.liveRangeEnd) {
+			continue;
+		}
+		if(si->data.var.usedefFirst == NULL) {
+			// Even if the resource is in use, the variable itself isn't so we don't care
+			continue;
+		}
+		if(!lr_empty(si) && (ast_stmt_is_after(tlc, statement, si->data.var.liveRangeStart) == 1
+			&& ast_stmt_is_after(tlc, si->data.var.liveRangeEnd, statement) == 1)) {
+			return true;
+		}
+	}
+	return false;
+}
+
 void cg_chunk(CGState *cg, AST *a) {
 	AST *s = a->chunk.statementFirst;
 	
@@ -390,12 +411,14 @@ void cg_chunk(CGState *cg, AST *a) {
 			
 			AST *e = s->stmtAssign.to;
 			
-			if(x86_ia16()) {
-				puts("push cx");
-				puts("push dx");
-			} else {
-				puts("push ecx");
-				puts("push edx");
+			if(is_resource_in_use_right_now_at_this_current_point_in_time_and_also_not_created_right_now(a, s, HWR_ECX)) {
+				puts(x86_ia16() ? "push cx" : "push ecx");
+			}
+			if(is_resource_in_use_right_now_at_this_current_point_in_time_and_also_not_created_right_now(a, s, HWR_EDX)) {
+				puts(x86_ia16() ? "push dx" : "push edx");
+			}
+			if(is_resource_in_use_right_now_at_this_current_point_in_time_and_also_not_created_right_now(a, s, HWR_EAX)) {
+				puts(x86_ia16() ? "push ax" : "push eax");
 			}
 			
 			int argCount = e->exprCall.what->expression.type->pointer.of->function.argCount;
@@ -422,12 +445,14 @@ void cg_chunk(CGState *cg, AST *a) {
 				}
 			}
 			
-			if(x86_ia16()) {
-				puts("pop dx");
-				puts("pop cx");
-			} else {
-				puts("pop edx");
-				puts("pop ecx");
+			if(is_resource_in_use_right_now_at_this_current_point_in_time_and_also_not_created_right_now(a, s, HWR_EAX)) {
+				puts(x86_ia16() ? "pop ax" : "pop eax");
+			}
+			if(is_resource_in_use_right_now_at_this_current_point_in_time_and_also_not_created_right_now(a, s, HWR_EDX)) {
+				puts(x86_ia16() ? "pop dx" : "pop edx");
+			}
+			if(is_resource_in_use_right_now_at_this_current_point_in_time_and_also_not_created_right_now(a, s, HWR_ECX)) {
+				puts(x86_ia16() ? "pop cx" : "pop ecx");
 			}
 			
 		} else if(s->nodeKind == AST_STMT_ASSIGN) {