[AMDGPU] Fix SIFoldOperandsImpl::tryFoldZeroHighBits when met non-reg src1 operand. (#133761)

This happens when a constant is propagated to a V_AND 0xFFFF, reg
instruction.

Fixes failures like:

```
llc: /github/llvm-project/llvm/include/llvm/CodeGen/MachineOperand.h:366: llvm::Register llvm::MachineOperand::getReg() const: Assertion `isReg() && "This is not a register operand!"' failed.
Stack dump:
0.      Program arguments: /github/llvm-project/build/Debug/bin/llc -mtriple=amdgcn -mcpu=gfx1101 -verify-machineinstrs -run-pass si-fold-operands /github/llvm-project/llvm/test/CodeGen/AMDGPU/fold-zero-high-bits-skips-non-reg.mir -o -
1.      Running pass 'Function Pass Manager' on module '/github/llvm-project/llvm/test/CodeGen/AMDGPU/fold-zero-high-bits-skips-non-reg.mir'.
2.      Running pass 'SI Fold Operands' on function '@test_tryFoldZeroHighBits_skips_nonreg'
...
#12 0x00007f5a55005cfc llvm::MachineOperand::getReg() const /github/llvm-project/llvm/include/llvm/CodeGen/MachineOperand.h:0:5
#13 0x00007f5a555c6bf5 (anonymous namespace)::SIFoldOperandsImpl::tryFoldZeroHighBits(llvm::MachineInstr&) const /github/llvm-project/llvm/lib/Target/AMDGPU/SIFoldOperands.cpp:1459:36
#14 0x00007f5a555c63ad (anonymous namespace)::SIFoldOperandsImpl::run(llvm::MachineFunction&) /github/llvm-project/llvm/lib/Target/AMDGPU/SIFoldOperands.cpp:2455:11
#15 0x00007f5a555c6780 (anonymous namespace)::SIFoldOperandsLegacy::runOnMachineFunction
```

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/lib/Target/AMDGPU/SIFoldOperands.cpp b/llvm/lib/Target/AMDGPU/SIFoldOperands.cpp
index cc15dd7..46bd5d8 100644
--- a/llvm/lib/Target/AMDGPU/SIFoldOperands.cpp
+++ b/llvm/lib/Target/AMDGPU/SIFoldOperands.cpp
@@ -1453,7 +1453,7 @@ bool SIFoldOperandsImpl::tryFoldZeroHighBits(MachineInstr &MI) const {
     return false;
 
   std::optional<int64_t> Src0Imm = getImmOrMaterializedImm(MI.getOperand(1));
-  if (!Src0Imm || *Src0Imm != 0xffff)
+  if (!Src0Imm || *Src0Imm != 0xffff || !MI.getOperand(2).isReg())
     return false;
 
   Register Src1 = MI.getOperand(2).getReg();