[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

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

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

llvm-svn: 343521
diff --git a/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp b/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp
index c4b9b45..a66f527 100644
--- a/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp
+++ b/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp
@@ -158,6 +158,7 @@
   initializeAArch64ExpandPseudoPass(*PR);
   initializeAArch64LoadStoreOptPass(*PR);
   initializeAArch64SIMDInstrOptPass(*PR);
+  initializeAArch64PreLegalizerCombinerPass(*PR);
   initializeAArch64PromoteConstantPass(*PR);
   initializeAArch64RedundantCopyEliminationPass(*PR);
   initializeAArch64StorePairSuppressPass(*PR);
@@ -348,6 +349,7 @@
   bool addPreISel() override;
   bool addInstSelector() override;
   bool addIRTranslator() override;
+  void addPreLegalizeMachineIR() override;
   bool addLegalizeMachineIR() override;
   bool addRegBankSelect() override;
   void addPreGlobalInstructionSelect() override;
@@ -449,6 +451,10 @@
   return false;
 }
 
+void AArch64PassConfig::addPreLegalizeMachineIR() {
+  addPass(createAArch64PreLegalizeCombiner());
+}
+
 bool AArch64PassConfig::addLegalizeMachineIR() {
   addPass(new Legalizer());
   return false;