[llvm] [X86][CodeGen] Fix crash when commute operands of Instruction for code size (PR #79245)

[Shengchen Kan via llvm-commits]

https://github.com/KanRobert created https://github.com/llvm/llvm-project/pull/79245

Reported in 134fcc62786d31ab73439201dce2d73808d1785a


>From ad9e2f81a4e44710314ac0e2b39cdc0b4aed0db3 Mon Sep 17 00:00:00 2001
From: Shengchen Kan <shengchen.kan at intel.com>
Date: Wed, 24 Jan 2024 11:01:44 +0800
Subject: [PATCH] [X86][CodeGen] Fix crash when commute operands of Instruction
 for code size

Reported in 134fcc62786d31ab73439201dce2d73808d1785a
---
 llvm/lib/Target/X86/X86InstrInfo.cpp | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/llvm/lib/Target/X86/X86InstrInfo.cpp b/llvm/lib/Target/X86/X86InstrInfo.cpp
index d6f9aa6d6acec0..6cdfecf1fe4d99 100644
--- a/llvm/lib/Target/X86/X86InstrInfo.cpp
+++ b/llvm/lib/Target/X86/X86InstrInfo.cpp
@@ -2355,29 +2355,30 @@ MachineInstr *X86InstrInfo::commuteInstructionImpl(MachineInstr &MI, bool NewMI,
     // If we're optimizing for size, try to use MOVSD/MOVSS.
     if (MI.getParent()->getParent()->getFunction().hasOptSize()) {
       unsigned Mask;
+      unsigned NewOpc;
       switch (Opc) {
       default:
         llvm_unreachable("Unreachable!");
       case X86::BLENDPDrri:
-        Opc = X86::MOVSDrr;
+        NewOpc = X86::MOVSDrr;
         Mask = 0x03;
         break;
       case X86::BLENDPSrri:
-        Opc = X86::MOVSSrr;
+        NewOpc = X86::MOVSSrr;
         Mask = 0x0F;
         break;
       case X86::VBLENDPDrri:
-        Opc = X86::VMOVSDrr;
+        NewOpc = X86::VMOVSDrr;
         Mask = 0x03;
         break;
       case X86::VBLENDPSrri:
-        Opc = X86::VMOVSSrr;
+        NewOpc = X86::VMOVSSrr;
         Mask = 0x0F;
         break;
       }
       if ((MI.getOperand(3).getImm() ^ Mask) == 1) {
         WorkingMI = CloneIfNew(MI);
-        WorkingMI->setDesc(get(Opc));
+        WorkingMI->setDesc(get(NewOpc));
         WorkingMI->removeOperand(3);
         break;
       }