From aab5c96b7eb237b8bcd15e28f8aff068842db4b7 Mon Sep 17 00:00:00 2001
From: David Neto <dneto@google.com>
Date: Tue, 3 Mar 2026 12:11:47 -0500
Subject: [PATCH] opt: Fix build issue with gcc 16  (replaeces PR #6542)
 (#6567)
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Compiling with gcc 16 throws this error:

FAILED: [code=1]
source/opt/CMakeFiles/SPIRV-Tools-opt.dir/decoration_manager.cpp.o
    source/opt/decoration_manager.cpp: In member function
‘spvtools::opt::analysis::DecorationManager::CloneDecorations(unsigned
int, unsigned int)’:
    source/opt/decoration_manager.cpp:546:27: error:
‘MEM[(unsigned int &)&op + 24]’ may be used uninitialized
[-Werror=maybe-uninitialized]

546 | if (op.words[0] == from) { // add new pair of operands: (to,
literal)
    source/opt/decoration_manager.cpp:545:19: note: ‘op’ declared here
      545 |           Operand op = inst->GetOperand(i);
          |                   ^~
    cc1plus: all warnings being treated as errors

Make sure that the vector is not empty before using it.

Co-authored-by: José Expósito <jose.exposito89@gmail.com>
Signed-off-by: Martin Jansa <martin.jansa@gmail.com>
Upstream-Status: Backport [c28f5937bce369dde1d645299a8c9873da43dc72]
---
 source/opt/decoration_manager.cpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/source/opt/decoration_manager.cpp b/source/opt/decoration_manager.cpp
index 3e95dbc35..bee7d9482 100644
--- a/source/opt/decoration_manager.cpp
+++ b/source/opt/decoration_manager.cpp
@@ -543,7 +543,8 @@ void DecorationManager::CloneDecorations(uint32_t from, uint32_t to) {
         const uint32_t num_operands = inst->NumOperands();
         for (uint32_t i = 1; i < num_operands; i += 2) {
           Operand op = inst->GetOperand(i);
-          if (op.words[0] == from) {  // add new pair of operands: (to, literal)
+          if (!op.words.empty() &&
+              op.words[0] == from) {  // add new pair of operands: (to, literal)
             inst->AddOperand(
                 Operand(spv_operand_type_t::SPV_OPERAND_TYPE_ID, {to}));
             op = inst->GetOperand(i + 1);
