[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

llvm-svn: 311038

1 files changed, 9 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/TargetPassConfig.cpp b/llvm/lib/CodeGen/TargetPassConfig.cpp
index 481baea2dff..7860a932c2b 100644
--- a/llvm/lib/CodeGen/TargetPassConfig.cpp
+++ b/llvm/lib/CodeGen/TargetPassConfig.cpp
@@ -88,6 +88,8 @@ static cl::opt<bool> DisableCGP("disable-cgp", cl::Hidden,
     cl::desc("Disable Codegen Prepare"));
 static cl::opt<bool> DisableCopyProp("disable-copyprop", cl::Hidden,
     cl::desc("Disable Copy Propagation pass"));
+static cl::opt<bool> DisableCopyPropPreRegRewrite("disable-copyprop-prerewrite", cl::Hidden,
+    cl::desc("Disable Copy Propagation Pre-Register Re-write pass"));
 static cl::opt<bool> DisablePartialLibcallInlining("disable-partial-libcall-inlining",
     cl::Hidden, cl::desc("Disable Partial Libcall Inlining"));
 static cl::opt<bool> EnableImplicitNullChecks(
@@ -248,6 +250,9 @@ static IdentifyingPassPtr overridePass(AnalysisID StandardID,
   if (StandardID == &MachineCopyPropagationID)
     return applyDisable(TargetID, DisableCopyProp);
 
+  if (StandardID == &MachineCopyPropagationPreRegRewriteID)
+    return applyDisable(TargetID, DisableCopyPropPreRegRewrite);
+
   return TargetID;
 }
 
@@ -1059,6 +1064,10 @@ void TargetPassConfig::addOptimizedRegAlloc(FunctionPass *RegAllocPass) {
     // Allow targets to change the register assignments before rewriting.
     addPreRewrite();
 
+    // Copy propagate to forward register uses and try to eliminate COPYs that
+    // were not coalesced.
+    addPass(&MachineCopyPropagationPreRegRewriteID);
+
     // Finally rewrite virtual registers.
     addPass(&VirtRegRewriterID);