[llvm] [AMDGPU] Save/Restore SCC bit across waterfall loop. (PR #68363)

[Sirish Pande via llvm-commits]

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@@ -5094,6 +5094,39 @@ unsigned SIInstrInfo::getVALUOp(const MachineInstr &MI) const {
       "Unexpected scalar opcode without corresponding vector one!");
 }
 
+bool SIInstrInfo::isSCCDefinedBefore(MachineBasicBlock &MBB,
+                                     MachineBasicBlock::iterator Before) const {
+
+  for (MachineBasicBlock::iterator I = Before, B = MBB.begin(); I != B; --I) {
+    MachineInstr &MI = *I;
+    if (!MI.hasImplicitDef())
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srpande wrote:

With `computeRegisterLiveness(Reg)`, this change won't be necessary.

https://github.com/llvm/llvm-project/pull/68363