[PATCH] D64035: [MachinePipeliner] Fix Phi refers to Phi in same stage in 1st epilogue

[Jinsong Ji via Phabricator via llvm-commits]

jsji created this revision.
jsji added reviewers: bcahoon, hfinkel.
Herald added subscribers: hiraditya, nemanjai.
Herald added a project: LLVM.

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.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D64035

Files:
  llvm/lib/CodeGen/MachinePipeliner.cpp
  llvm/test/CodeGen/PowerPC/sms-phi.ll


Index: llvm/test/CodeGen/PowerPC/sms-phi.ll
===================================================================
--- llvm/test/CodeGen/PowerPC/sms-phi.ll
+++ llvm/test/CodeGen/PowerPC/sms-phi.ll
@@ -8,7 +8,7 @@
 ;CHECK: epilog:
 ;CHECK:        %23:g8rc_and_g8rc_nox0 = PHI %5:g8rc_and_g8rc_nox0, %bb.3, %18:g8rc_and_g8rc_nox0, %bb.4
 ;CHECK-NEXT:   %24:g8rc = PHI %6:g8rc, %bb.3, %16:g8rc, %bb.4
-;CHECK-NEXT:   %25:g8rc = PHI %6:g8rc, %bb.3, %16:g8rc, %bb.4
+;CHECK-NEXT:   %25:g8rc = PHI %6:g8rc, %bb.3, %19:g8rc, %bb.4
   br label %1
 
 1:                                                ; preds = %1, %0
Index: llvm/lib/CodeGen/MachinePipeliner.cpp
===================================================================
--- llvm/lib/CodeGen/MachinePipeliner.cpp
+++ llvm/lib/CodeGen/MachinePipeliner.cpp
@@ -2430,7 +2430,7 @@
         // 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];
       }
 


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