[AMDGPU] SILowerControlFlow: ensure EXEC/SCC interval recompute (#160459)

Ensure live intervals for EXEC and SCC are removed on all paths which
generate instructions.

Author: perlfu

llvm/lib/Target/AMDGPU/SILowerControlFlow.cpp

@@ -293,7 +293,6 @@ void SILowerControlFlow::emitIf(MachineInstr &MI) {
   LIS->InsertMachineInstrInMaps(*SetExec);
   LIS->InsertMachineInstrInMaps(*NewBr);
 
-  LIS->removeAllRegUnitsForPhysReg(AMDGPU::EXEC);
   MI.eraseFromParent();
 
   // FIXME: Is there a better way of adjusting the liveness? It shouldn't be
@@ -363,9 +362,6 @@ void SILowerControlFlow::emitElse(MachineInstr &MI) {
   RecomputeRegs.insert(SrcReg);
   RecomputeRegs.insert(DstReg);
   LIS->createAndComputeVirtRegInterval(SaveReg);
-
-  // Let this be recomputed.
-  LIS->removeAllRegUnitsForPhysReg(AMDGPU::EXEC);
 }
 
 void SILowerControlFlow::emitIfBreak(MachineInstr &MI) {
@@ -828,7 +824,10 @@ bool SILowerControlFlow::run(MachineFunction &MF) {
 
   optimizeEndCf();
 
-  if (LIS) {
+  if (LIS && Changed) {
+    // These will need to be recomputed for insertions and removals.
+    LIS->removeAllRegUnitsForPhysReg(AMDGPU::EXEC);
+    LIS->removeAllRegUnitsForPhysReg(AMDGPU::SCC);
     for (Register Reg : RecomputeRegs) {
       LIS->removeInterval(Reg);
       LIS->createAndComputeVirtRegInterval(Reg);