Enable the reuse of values computed in a previous loop iteration.

This patch adds a pass that removes the computation of provably redundant
expressions that have been computed earlier in a previous iteration. It
relies on the use of PHIs to identify loop carried dependences.

This is scalar replacement for vector types.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@313925 91177308-0d34-0410-b5e6-96231b3b80d8

Author: pranavb-ca

lib/Target/Hexagon/CMakeLists.txt

@@ -53,6 +53,7 @@ add_llvm_target(HexagonCodeGen
   HexagonTargetMachine.cpp
   HexagonTargetObjectFile.cpp
   HexagonTargetTransformInfo.cpp
+  HexagonVectorLoopCarriedReuse.cpp
   HexagonVectorPrint.cpp
   HexagonVLIWPacketizer.cpp
   RDFCopy.cpp

lib/Target/Hexagon/HexagonTargetMachine.cpp

@@ -123,10 +123,12 @@ namespace llvm {
   void initializeHexagonExpandCondsetsPass(PassRegistry&);
   void initializeHexagonGenMuxPass(PassRegistry&);
   void initializeHexagonLoopIdiomRecognizePass(PassRegistry&);
+  void initializeHexagonVectorLoopCarriedReusePass(PassRegistry&);
   void initializeHexagonNewValueJumpPass(PassRegistry&);
   void initializeHexagonOptAddrModePass(PassRegistry&);
   void initializeHexagonPacketizerPass(PassRegistry&);
   Pass *createHexagonLoopIdiomPass();
+  Pass *createHexagonVectorLoopCarriedReusePass();
 
   FunctionPass *createHexagonBitSimplify();
   FunctionPass *createHexagonBranchRelaxation();
@@ -177,6 +179,7 @@ extern "C" void LLVMInitializeHexagonTarget() {
   initializeHexagonEarlyIfConversionPass(PR);
   initializeHexagonGenMuxPass(PR);
   initializeHexagonLoopIdiomRecognizePass(PR);
+  initializeHexagonVectorLoopCarriedReusePass(PR);
   initializeHexagonNewValueJumpPass(PR);
   initializeHexagonOptAddrModePass(PR);
   initializeHexagonPacketizerPass(PR);
@@ -237,6 +240,11 @@ void HexagonTargetMachine::adjustPassManager(PassManagerBuilder &PMB) {
     [&](const PassManagerBuilder &, legacy::PassManagerBase &PM) {
       PM.add(createHexagonLoopIdiomPass());
     });
+  PMB.addExtension(
+    PassManagerBuilder::EP_LoopOptimizerEnd,
+    [&](const PassManagerBuilder &, legacy::PassManagerBase &PM) {
+      PM.add(createHexagonVectorLoopCarriedReusePass());
+    });
 }
 
 TargetIRAnalysis HexagonTargetMachine::getTargetIRAnalysis() {