[globalisel] Add a combiner helpers for extending loads and use them in a pre-legalize combiner for AArch64

Summary: Depends on D45541

Reviewers: ab, aditya_nandakumar, bogner, rtereshin, volkan, rovka, javed.absar, aemerson

Reviewed By: aemerson

Subscribers: aemerson, rengolin, mgorny, javed.absar, kristof.beyls, llvm-commits

Differential Revision: https://reviews.llvm.org/D45543

llvm-svn: 331816

1 files changed, 33 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
index 44e904a6391..25b40da4dd7 100644
--- a/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
@@ -36,6 +36,38 @@ bool CombinerHelper::tryCombineCopy(MachineInstr &MI) {
   return false;
 }
 
+bool CombinerHelper::tryCombineExtendingLoads(MachineInstr &MI) {
+  unsigned DstReg = MI.getOperand(0).getReg();
+  unsigned SrcReg = MI.getOperand(1).getReg();
+
+  if (MI.getOpcode() != TargetOpcode::G_ANYEXT &&
+      MI.getOpcode() != TargetOpcode::G_SEXT &&
+      MI.getOpcode() != TargetOpcode::G_ZEXT)
+    return false;
+
+  LLT DstTy = MRI.getType(DstReg);
+  if (!DstTy.isScalar())
+    return false;
+
+  if (MachineInstr *DefMI = getOpcodeDef(TargetOpcode::G_LOAD, SrcReg, MRI)) {
+    unsigned PtrReg = DefMI->getOperand(1).getReg();
+    MachineMemOperand &MMO = **DefMI->memoperands_begin();
+    DEBUG(dbgs() << ".. Combine MI: " << MI;);
+    Builder.setInstr(MI);
+    Builder.buildLoadInstr(MI.getOpcode() == TargetOpcode::G_SEXT
+                               ? TargetOpcode::G_SEXTLOAD
+                               : MI.getOpcode() == TargetOpcode::G_ZEXT
+                                     ? TargetOpcode::G_ZEXTLOAD
+                                     : TargetOpcode::G_LOAD,
+                           DstReg, PtrReg, MMO);
+    MI.eraseFromParent();
+    return true;
+  }
+  return false;
+}
+
 bool CombinerHelper::tryCombine(MachineInstr &MI) {
-  return tryCombineCopy(MI);
+  if (tryCombineCopy(MI))
+    return true;
+  return tryCombineExtendingLoads(MI);;
 }