[AMDGPU] Invert the handling of skip insertion.

The current implementation of skip insertion (SIInsertSkip) makes it a
mandatory pass required for correctness. Initially, the idea was to
have an optional pass. This patch inserts the s_cbranch_execz upfront
during SILowerControlFlow to skip over the sections of code when no
lanes are active. Later, SIRemoveShortExecBranches removes the skips
for short branches, unless there is a sideeffect and the skip branch is
really necessary.

This new pass will replace the handling of skip insertion in the
existing SIInsertSkip Pass.

Differential revision: https://reviews.llvm.org/D68092

1 files changed, 2 insertions, 0 deletions

diff --git a/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp b/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
index c8dc6f6e3bf..eb30d659bf0 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
@@ -228,6 +228,7 @@ extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeAMDGPUTarget() {
   initializeSIModeRegisterPass(*PR);
   initializeSIWholeQuadModePass(*PR);
   initializeSILowerControlFlowPass(*PR);
+  initializeSIRemoveShortExecBranchesPass(*PR);
   initializeSIInsertSkipsPass(*PR);
   initializeSIMemoryLegalizerPass(*PR);
   initializeSIOptimizeExecMaskingPass(*PR);
@@ -993,6 +994,7 @@ void GCNPassConfig::addPreEmitPass() {
   // be better for it to emit S_NOP <N> when possible.
   addPass(&PostRAHazardRecognizerID);
 
+  addPass(&SIRemoveShortExecBranchesID);
   addPass(&SIInsertSkipsPassID);
   addPass(&BranchRelaxationPassID);
 }