[MachinePipeliner] Fix Phi refers to Phi in same stage in 1st epilogue

Summary:
This is exposed by functional testing on PowerPC.
In some pipelined loops, Phi refer to phi did not get value defined by
the Phi, hence getting wrong value later.

As the comment mentioned, we should "use the value defined by the Phi,
unless we're generating the firstepilog and the Phi refers to a Phi
 in a different stage.", so Phi refering to same stage Phi should use
the value defined by the Phi here.

Reviewers: bcahoon, hfinkel

Reviewed By: hfinkel

Subscribers: MaskRay, wuzish, nemanjai, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D64035

llvm-svn: 365428

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/MachinePipeliner.cpp b/llvm/lib/CodeGen/MachinePipeliner.cpp
index 167c05f9ef4..9c0c5cc5c70 100644
--- a/llvm/lib/CodeGen/MachinePipeliner.cpp
+++ b/llvm/lib/CodeGen/MachinePipeliner.cpp
@@ -2430,7 +2430,7 @@ void SwingSchedulerDAG::generateExistingPhis(
         // Use the value defined by the Phi, unless we're generating the first
         // epilog and the Phi refers to a Phi in a different stage.
         else if (VRMap[PrevStage - np].count(Def) &&
-                 (!LoopDefIsPhi || PrevStage != LastStageNum))
+                 (!LoopDefIsPhi || (PrevStage != LastStageNum) || (LoopValStage == StageScheduled)))
           PhiOp2 = VRMap[PrevStage - np][Def];
       }