[llvm] [AMDGPU] fix eliminateFrameIndex to use SGPR frame index (PR #178991)

[via llvm-commits]

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@@ -3077,7 +3077,15 @@ bool SIRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator MI,
     if (!IsMUBUF && !MFI->isBottomOfStack()) {
       // Convert to a swizzled stack address by scaling by the wave size.
       // In an entry function/kernel the offset is already swizzled.
-      bool IsSALU = isSGPRClass(TII->getRegClass(MI->getDesc(), FIOperandNum));
+      const TargetRegisterClass *FiRC =
+          TII->getRegClass(MI->getDesc(), FIOperandNum);
+      bool IsSALU = false;
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bcahoon wrote:

bool IsSALU = FiRC && isSGPRClass(FiRC);

https://github.com/llvm/llvm-project/pull/178991