[llvm] [AArch64] Avoid applying S-form on frame index in peephole (PR #158597)

[Sander de Smalen via llvm-commits]

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@@ -1920,6 +1920,11 @@ static bool canInstrSubstituteCmpInstr(MachineInstr &MI, MachineInstr &CmpInstr,
           CmpInstr.getOperand(2).getImm() == 0) &&
          "Caller guarantees that CmpInstr compares with constant 0");
 
+  // NZCV is not supported if the stack offset is scalable.
+  auto &ST = MI.getParent()->getParent()->getSubtarget<AArch64Subtarget>();
+  if ((ST.hasSVE() || ST.isStreaming()) && MI.getOperand(1).isFI())
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sdesmalen-arm wrote:

Nothing here is checking that the stack offset is scalable. If you want to know if the frame-index is describing an object on the stack with scalable size, then you should like at its stack ID.

https://github.com/llvm/llvm-project/pull/158597