[MachineCopyPropagation] Extend pass to do COPY source forwarding

This change extends MachineCopyPropagation to do COPY source forwarding.

This change also extends the MachineCopyPropagation pass to be able to
be run during register allocation, after physical registers have been
assigned, but before the virtual registers have been re-written, which
allows it to remove virtual register COPY LiveIntervals that become dead
through the forwarding of all of their uses.

Reviewers: qcolombet, javed.absar, MatzeB, jonpa

Subscribers: jyknight, nemanjai, llvm-commits, nhaehnle, mcrosier, mgorny

Differential Revision: https://reviews.llvm.org/D30751

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@311038 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/Passes.h

@@ -278,6 +278,11 @@ namespace llvm {
   /// MachineSinking - This pass performs sinking on machine instructions.
   extern char &MachineSinkingID;
 
+  /// MachineCopyPropagationPreRegRewrite - This pass performs copy propagation
+  /// on machine instructions after register allocation but before virtual
+  /// register re-writing..
+  extern char &MachineCopyPropagationPreRegRewriteID;
+
   /// MachineCopyPropagation - This pass performs copy propagation on
   /// machine instructions.
   extern char &MachineCopyPropagationID;

include/llvm/InitializePasses.h

@@ -233,6 +233,7 @@ void initializeMachineBranchProbabilityInfoPass(PassRegistry&);
 void initializeMachineCSEPass(PassRegistry&);
 void initializeMachineCombinerPass(PassRegistry&);
 void initializeMachineCopyPropagationPass(PassRegistry&);
+void initializeMachineCopyPropagationPreRegRewritePass(PassRegistry&);
 void initializeMachineDominanceFrontierPass(PassRegistry&);
 void initializeMachineDominatorTreePass(PassRegistry&);
 void initializeMachineFunctionPrinterPassPass(PassRegistry&);

lib/CodeGen/CodeGen.cpp

@@ -54,6 +54,7 @@ void llvm::initializeCodeGen(PassRegistry &Registry) {
   initializeMachineCSEPass(Registry);
   initializeMachineCombinerPass(Registry);
   initializeMachineCopyPropagationPass(Registry);
+  initializeMachineCopyPropagationPreRegRewritePass(Registry);
   initializeMachineDominatorTreePass(Registry);
   initializeMachineFunctionPrinterPassPass(Registry);
   initializeMachineLICMPass(Registry);