[PPCMIPeephole] Fix splat elimination

Summary:
In PPCMIPeephole, when we see two splat instructions, we can't simply do the following transformation:
  B = Splat A
  C = Splat B
=>
  C = Splat A
because B may still be used between these two instructions. Instead, we should make the second Splat a PPC::COPY and let later passes decide whether to remove it or not:
  B = Splat A
  C = Splat B
=>
  B = Splat A
  C = COPY B

Fixes PR30663.

Reviewers: echristo, iteratee, kbarton, nemanjai

Subscribers: mehdi_amini, llvm-commits

Differential Revision: https://reviews.llvm.org/D25493


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@283961 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 5 insertions, 3 deletions

diff --git a/lib/Target/PowerPC/PPCMIPeephole.cpp b/lib/Target/PowerPC/PPCMIPeephole.cpp
index 3360e74db99..ee62bb3b500 100644
--- a/lib/Target/PowerPC/PPCMIPeephole.cpp
+++ b/lib/Target/PowerPC/PPCMIPeephole.cpp
@@ -201,11 +201,13 @@ bool PPCMIPeephole::simplifyCode(void) {
         // Splat fed by another splat - switch the output of the first
         // and remove the second.
         if (SameOpcode) {
-          DefMI->getOperand(0).setReg(MI.getOperand(0).getReg());
+          DEBUG(dbgs() << "Changing redundant splat to a copy: ");
+          DEBUG(MI.dump());
+          BuildMI(MBB, &MI, MI.getDebugLoc(), TII->get(PPC::COPY),
+                  MI.getOperand(0).getReg())
+              .addOperand(MI.getOperand(OpNo));
           ToErase = &MI;
           Simplified = true;
-          DEBUG(dbgs() << "Removing redundant splat: ");
-          DEBUG(MI.dump());
         }
         // Splat fed by a shift. Usually when we align value to splat into
         // vector element zero.