[PATCH] D23513: Fix assert in pipeliner due to an invalid Phi in the epilog

[Brendon Cahoon via llvm-commits]

bcahoon created this revision.
bcahoon added a reviewer: kparzysz.
bcahoon added a subscriber: llvm-commits.

The pipeliner was generating an invalid Phi name for an operand in the epilog block, which caused an assert in the live variable analysis pass. The fix is to the code that generates new Phis in the epilog block. In this case, there is an existing Phi that needs to be reused rather than creating a new Phi instruction.


https://reviews.llvm.org/D23513

Files:
  lib/CodeGen/MachinePipeliner.cpp
  test/CodeGen/Hexagon/swp-epilog-reuse-1.ll

Index: test/CodeGen/Hexagon/swp-epilog-reuse-1.ll
===================================================================
--- /dev/null
+++ test/CodeGen/Hexagon/swp-epilog-reuse-1.ll
@@ -0,0 +1,44 @@
+; RUN: llc -march=hexagon -mcpu=hexagonv60 < %s
+; REQUIRES: asserts
+
+; Test that the pipeliner reuses an existing Phi when generating the epilog
+; block. In this case, the original loops has a Phi whose operand is another
+; Phi. When the loop is pipelined, the Phi that generates the operand value
+; is used in two stages. This means the the Phi for the second stage can
+; be reused. The bug causes an assert due to an invalid virtual register error
+; in the live variable analysis.
+
+define void @test(i8* %a, i8* %b)  #0 {
+entry:
+  br label %for.body6.us.prol
+
+for.body6.us.prol:
+  %i.065.us.prol = phi i32 [ 0, %entry ], [ %inc.us.prol, %for.body6.us.prol ]
+  %im1.064.us.prol = phi i32 [ undef, %entry ], [ %i.065.us.prol, %for.body6.us.prol ]
+  %prol.iter = phi i32 [ undef, %entry ], [ %prol.iter.sub, %for.body6.us.prol ]
+  %arrayidx8.us.prol = getelementptr inbounds i8, i8* %b, i32 %im1.064.us.prol
+  %0 = load i8, i8* %arrayidx8.us.prol, align 1
+  %conv9.us.prol = sext i8 %0 to i32
+  %add.us.prol = add nsw i32 %conv9.us.prol, 0
+  %add12.us.prol = add nsw i32 %add.us.prol, 0
+  %mul.us.prol = mul nsw i32 %add12.us.prol, 3
+  %conv13.us.prol = trunc i32 %mul.us.prol to i8
+  %arrayidx14.us.prol = getelementptr inbounds i8, i8* %a, i32 %i.065.us.prol
+  store i8 %conv13.us.prol, i8* %arrayidx14.us.prol, align 1
+  %inc.us.prol = add nuw nsw i32 %i.065.us.prol, 1
+  %prol.iter.sub = add i32 %prol.iter, -1
+  %prol.iter.cmp = icmp eq i32 %prol.iter.sub, 0
+  br i1 %prol.iter.cmp, label %for.body6.us, label %for.body6.us.prol
+
+for.body6.us:
+  %im2.063.us = phi i32 [ undef, %for.body6.us ], [ %im1.064.us.prol, %for.body6.us.prol ]
+  %arrayidx10.us = getelementptr inbounds i8, i8* %b, i32 %im2.063.us
+  %1 = load i8, i8* %arrayidx10.us, align 1
+  %conv11.us = sext i8 %1 to i32
+  %add12.us = add nsw i32 0, %conv11.us
+  %mul.us = mul nsw i32 %add12.us, 3
+  %conv13.us = trunc i32 %mul.us to i8
+  store i8 %conv13.us, i8* undef, align 1
+  br label %for.body6.us
+}
+
Index: lib/CodeGen/MachinePipeliner.cpp
===================================================================
--- lib/CodeGen/MachinePipeliner.cpp
+++ lib/CodeGen/MachinePipeliner.cpp
@@ -2648,8 +2648,7 @@
       // references another Phi, and the other Phi is scheduled in an
       // earlier stage. We can try to reuse an existing Phi up until the last
       // stage of the current Phi.
-      if (LoopDefIsPhi && VRMap[CurStageNum].count(LoopVal) &&
-          LoopValStage >= (int)(CurStageNum - LastStageNum)) {
+      if (LoopDefIsPhi && (int)PrologStage >= StageScheduled) {
         int LVNumStages = Schedule.getStagesForPhi(LoopVal);
         int StageDiff = (StageScheduled - LoopValStage);
         LVNumStages -= StageDiff;


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