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

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-x86

Author: Shengchen Kan (KanRobert)

<details>
<summary>Changes</summary>

Reported in 134fcc62786d31ab73439201dce2d73808d1785a


---
Full diff: https://github.com/llvm/llvm-project/pull/79245.diff


1 Files Affected:

- (modified) llvm/lib/Target/X86/X86InstrInfo.cpp (+6-5) 


``````````diff
diff --git a/llvm/lib/Target/X86/X86InstrInfo.cpp b/llvm/lib/Target/X86/X86InstrInfo.cpp
index d6f9aa6d6acec09..6cdfecf1fe4d99e 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;
       }

``````````

</details>


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