AMDGPU: Remove PHI loop condition optimization

Summary:
The optimization to early break out of loops if all threads are dead was
never fully implemented.

But the PHI node analyzing is actually causing a number of problems, so
remove all the extra code for it.

(This does actually regress code quality in a few places because it
 ends up relying more heavily on phi's of i1, which we don't do a
 great job with. However, since it fixes real bugs in the wild, we
 should take this change. I have some prototype changes to improve
 i1 lowering in general -- not just for control flow -- which should
 help recover the code quality, I just need to make those changes
 fit for general consumption. -- Nicolai)

Change-Id: I6fc6c6c8961857ac6009fcfb9f7e5e48dc23fbb1
Patch-by: Christian König <christian.koenig@amd.com>

Reviewers: arsenm, rampitec, tpr

Subscribers: kzhuravl, jvesely, wdng, yaxunl, dstuttard, t-tye, llvm-commits

Differential Revision: https://reviews.llvm.org/D53359

llvm-svn: 345718

1 files changed, 0 insertions, 29 deletions

diff --git a/llvm/lib/Target/AMDGPU/SILowerControlFlow.cpp b/llvm/lib/Target/AMDGPU/SILowerControlFlow.cpp
index ad30317c344..1aa1feebbda 100644
--- a/llvm/lib/Target/AMDGPU/SILowerControlFlow.cpp
+++ b/llvm/lib/Target/AMDGPU/SILowerControlFlow.cpp
@@ -85,9 +85,7 @@ private:
 
   void emitIf(MachineInstr &MI);
   void emitElse(MachineInstr &MI);
-  void emitBreak(MachineInstr &MI);
   void emitIfBreak(MachineInstr &MI);
-  void emitElseBreak(MachineInstr &MI);
   void emitLoop(MachineInstr &MI);
   void emitEndCf(MachineInstr &MI);
 
@@ -329,20 +327,6 @@ void SILowerControlFlow::emitElse(MachineInstr &MI) {
   LIS->removeRegUnit(*MCRegUnitIterator(AMDGPU::EXEC, TRI));
 }
 
-void SILowerControlFlow::emitBreak(MachineInstr &MI) {
-  MachineBasicBlock &MBB = *MI.getParent();
-  const DebugLoc &DL = MI.getDebugLoc();
-  unsigned Dst = MI.getOperand(0).getReg();
-
-  MachineInstr *Or = BuildMI(MBB, &MI, DL, TII->get(AMDGPU::S_OR_B64), Dst)
-                         .addReg(AMDGPU::EXEC)
-                         .add(MI.getOperand(1));
-
-  if (LIS)
-    LIS->ReplaceMachineInstrInMaps(MI, *Or);
-  MI.eraseFromParent();
-}
-
 void SILowerControlFlow::emitIfBreak(MachineInstr &MI) {
   MachineBasicBlock &MBB = *MI.getParent();
   const DebugLoc &DL = MI.getDebugLoc();
@@ -384,11 +368,6 @@ void SILowerControlFlow::emitIfBreak(MachineInstr &MI) {
   MI.eraseFromParent();
 }
 
-void SILowerControlFlow::emitElseBreak(MachineInstr &MI) {
-  // Lowered in the same way as emitIfBreak above.
-  emitIfBreak(MI);
-}
-
 void SILowerControlFlow::emitLoop(MachineInstr &MI) {
   MachineBasicBlock &MBB = *MI.getParent();
   const DebugLoc &DL = MI.getDebugLoc();
@@ -515,18 +494,10 @@ bool SILowerControlFlow::runOnMachineFunction(MachineFunction &MF) {
         emitElse(MI);
         break;
 
-      case AMDGPU::SI_BREAK:
-        emitBreak(MI);
-        break;
-
       case AMDGPU::SI_IF_BREAK:
         emitIfBreak(MI);
         break;
 
-      case AMDGPU::SI_ELSE_BREAK:
-        emitElseBreak(MI);
-        break;
-
       case AMDGPU::SI_LOOP:
         emitLoop(MI);
         break;