From 46fc55e27390ea85eb34ec0367f40426197c9b9f Mon Sep 17 00:00:00 2001
From: lemon <lsof@mailbox.org>
Date: Thu, 19 Mar 2026 11:51:13 +0100
Subject: regalloc & emit: explicit comparisons over memcmp of small structures

The one in x86-64_emit was not portable due to relying on zero
initialization of inactive union fields/padding.
---
 src/ir_regalloc.c   |  2 +-
 src/t_x86-64_emit.c | 20 ++++++++++++++++++--
 2 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/src/ir_regalloc.c b/src/ir_regalloc.c
index ddb05e2..54f5d59 100644
--- a/src/ir_regalloc.c
+++ b/src/ir_regalloc.c
@@ -210,7 +210,7 @@ typedef struct {
 static void
 pmadd(PMState *pms, enum irclass k, Alloc dst, Alloc src)
 {
-   if (!memcmp(&dst, &src, sizeof dst)) return;
+   if (dst.bits == src.bits) return;
    assert(pms->npmove < MAXREGS);
    pms->pmove[pms->npmove++] = (struct PMove) { k, PMTOMOVE, dst, src };
 }
diff --git a/src/t_x86-64_emit.c b/src/t_x86-64_emit.c
index e1df982..507955a 100644
--- a/src/t_x86-64_emit.c
+++ b/src/t_x86-64_emit.c
@@ -160,6 +160,22 @@ mkmemoper(Ref r)
    }
 }
 
+static bool
+opereql(Oper a, Oper b)
+{
+   if (a.t != b.t) return 0;
+   switch (a.t) {
+   case OREG: return a.reg == b.reg;
+   case OIMM: return a.imm == b.imm;
+   case OMEM:
+      return a.base == b.base && a.index == b.index && a.shift == b.shift && a.disp == b.disp;
+   case OSYM:
+   case OSYMGOT:
+      return a.cindex == b.cindex && a.cshift == b.cshift && a.con == b.con && a.disp == b.disp;
+   default: assert(0);
+   }
+}
+
 /** Instruction description tables **
  *
  * Each instruction is a list of descs, and the first one that matches
@@ -703,7 +719,7 @@ static const EncDesc imul3_imm8tab[] = {
 static void
 Ximul(uchar **pcode, enum irclass k, Oper dst, Oper s1, Oper s2)
 {
-   if (!memcmp(&dst, &s1, sizeof dst) && s2.t != OIMM) {
+   if (opereql(dst, s1) && s2.t != OIMM) {
       Ximul2(pcode, k, dst, s2);
       return;
    }
@@ -908,7 +924,7 @@ gencopy(uchar **pcode, enum irclass cls, Block *blk, int curi, Oper dst, Ref val
       *pcode += 8;
    } else {
       Oper src = mkimmdatregoper(val);
-      if (memcmp(&dst, &src, sizeof dst) != 0)
+      if (!opereql(dst, src))
          Xmov(pcode, cls == KF64 && src.t == OREG && src.reg < XMM0 ? KI64 : cls, dst, src);
    }
 }
-- 
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