From cff611711ba54d6bd7b0ab02426419ceab4f7f07 Mon Sep 17 00:00:00 2001
From: Colin Leroy-Mira <colin@colino.net>
Date: Sun, 5 Nov 2023 21:03:06 +0100
Subject: [PATCH] Optimize multiplication by zero

---
 src/cc65/codegen.c | 14 +++++++++++++-
 test/val/mult1.c   |  1 +
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/src/cc65/codegen.c b/src/cc65/codegen.c
index 480cc32ead..f923ac8c9e 100644
--- a/src/cc65/codegen.c
+++ b/src/cc65/codegen.c
@@ -2726,7 +2726,12 @@ void g_mul (unsigned flags, unsigned long val)
                 if (flags & CF_FORCECHAR) {
                     /* Handle some special cases */
                     switch (val) {
-
+                        case 0:
+                            AddCodeLine ("lda #$00");
+                            return;
+                        case 1:
+                            /* Nothing to do */
+                            return;
                         case 3:
                             AddCodeLine ("sta tmp1");
                             AddCodeLine ("asl a");
@@ -2764,6 +2769,13 @@ void g_mul (unsigned flags, unsigned long val)
 
             case CF_INT:
                 switch (val) {
+                    case 0:
+                        AddCodeLine ("lda #$00");
+                        AddCodeLine ("tax");
+                        return;
+                    case 1:
+                        /* Nothing to do */
+                        return;
                     case 3:
                         AddCodeLine ("jsr mulax3");
                         return;
diff --git a/test/val/mult1.c b/test/val/mult1.c
index 95141d76d0..b1a074e41c 100644
--- a/test/val/mult1.c
+++ b/test/val/mult1.c
@@ -55,6 +55,7 @@ void m3(unsigned char uc)
   /* testing literal multiply with same source and destination */
   vuc = uc;
   uc2 = 0;
+  uc1 = vuc; uc1 = uc1*0; if( uc1 != 0 )              failures++;
   uc1 = vuc; uc1 = uc1*1; if( uc1 != (uc2+=TESTLIT) ) failures++;
   uc1 = vuc; uc1 = uc1*2; if( uc1 != (uc2+=TESTLIT) ) failures++;
   uc1 = vuc; uc1 = uc1*3; if( uc1 != (uc2+=TESTLIT) ) failures++;