[gicombiner] Hoist pure C++ combine into the tablegen definition

Summary:
This is just moving the existing C++ code around and will be NFC w.r.t
AArch64. Renamed 'CombineBr' to something more descriptive
('ElideByByInvertingCond') at the same time.

The remaining combines in AArch64PreLegalizeCombiner require features that
aren't implemented at this point and will be hoisted as they are added.

Depends on D68424

Reviewers: bogner, volkan

Subscribers: kristof.beyls, hiraditya, Petar.Avramovic, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D68426

llvm-svn: 375057

1 files changed, 11 insertions, 5 deletions

diff --git a/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
index e9de6c2c98d..da78327ebdb 100644
--- a/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
@@ -561,8 +561,10 @@ bool CombinerHelper::tryCombineIndexedLoadStore(MachineInstr &MI) {
   return true;
 }
 
-bool CombinerHelper::matchCombineBr(MachineInstr &MI) {
-  assert(MI.getOpcode() == TargetOpcode::G_BR && "Expected a G_BR");
+bool CombinerHelper::matchElideBrByInvertingCond(MachineInstr &MI) {
+  if (MI.getOpcode() != TargetOpcode::G_BR)
+    return false;
+
   // Try to match the following:
   // bb1:
   //   %c(s32) = G_ICMP pred, %a, %b
@@ -599,9 +601,14 @@ bool CombinerHelper::matchCombineBr(MachineInstr &MI) {
   return true;
 }
 
-bool CombinerHelper::tryCombineBr(MachineInstr &MI) {
-  if (!matchCombineBr(MI))
+bool CombinerHelper::tryElideBrByInvertingCond(MachineInstr &MI) {
+  if (!matchElideBrByInvertingCond(MI))
     return false;
+  applyElideBrByInvertingCond(MI);
+  return true;
+}
+
+void CombinerHelper::applyElideBrByInvertingCond(MachineInstr &MI) {
   MachineBasicBlock *BrTarget = MI.getOperand(0).getMBB();
   MachineBasicBlock::iterator BrIt(MI);
   MachineInstr *BrCond = &*std::prev(BrIt);
@@ -620,7 +627,6 @@ bool CombinerHelper::tryCombineBr(MachineInstr &MI) {
   BrCond->getOperand(1).setMBB(BrTarget);
   Observer.changedInstr(*BrCond);
   MI.eraseFromParent();
-  return true;
 }
 
 static bool shouldLowerMemFuncForSize(const MachineFunction &MF) {