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Fix a bug in vectorization of if-converted reduction variables. If the
reduction variable is not used outside the loop then we ran into an endless loop. This change checks if we found the original PHI. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169324 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -1985,20 +1985,20 @@ bool LoopVectorizationLegality::AddReductionVar(PHINode *Phi,
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// Also, we can't have multiple block-local users.
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Instruction *Iter = Phi;
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while (true) {
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// Any reduction instr must be of one of the allowed kinds.
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if (!isReductionInstr(Iter, Kind))
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return false;
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// Did we found a user inside this block ?
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bool FoundInBlockUser = false;
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// Did we reach the initial PHI node ?
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bool FoundStartPHI = false;
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// If the instruction has no users then this is a broken
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// chain and can't be a reduction variable.
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if (Iter->use_empty())
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return false;
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// Any reduction instr must be of one of the allowed kinds.
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if (!isReductionInstr(Iter, Kind))
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return false;
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// Did we find a user inside this block ?
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bool FoundInBlockUser = false;
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// Did we reach the initial PHI node ?
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bool FoundStartPHI = false;
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// For each of the *users* of iter.
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for (Value::use_iterator it = Iter->use_begin(), e = Iter->use_end();
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it != e; ++it) {
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@ -2009,21 +2009,22 @@ bool LoopVectorizationLegality::AddReductionVar(PHINode *Phi,
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continue;
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}
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// We allow in-loop PHINodes which are not the original reduction PHI
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// node. If this PHI is the only user of Iter (happens in IF w/ no ELSE
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// structure) then don't skip this PHI.
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if (isa<PHINode>(U) && U->getParent() != TheLoop->getHeader() &&
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TheLoop->contains(U->getParent()) && Iter->getNumUses() > 1)
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continue;
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// Check if we found the exit user.
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BasicBlock *Parent = U->getParent();
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if (!TheLoop->contains(Parent)) {
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// We must have a single exit instruction.
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// Exit if you find multiple outside users.
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if (ExitInstruction != 0)
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return false;
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ExitInstruction = Iter;
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}
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// We allow in-loop PHINodes which are not the original reduction PHI
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// node. If this PHI is the only user of Iter (happens in IF w/ no ELSE
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// structure) then don't skip this PHI.
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if (isa<PHINode>(U) && U->getParent() != TheLoop->getHeader() &&
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TheLoop->contains(U) && Iter->getNumUses() > 1)
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continue;
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// We can't have multiple inside users.
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if (FoundInBlockUser)
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return false;
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@ -2043,6 +2044,11 @@ bool LoopVectorizationLegality::AddReductionVar(PHINode *Phi,
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Reductions[Phi] = RD;
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return true;
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}
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// If we've reached the start PHI but did not find an outside user then
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// this is dead code. Abort.
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if (FoundStartPHI)
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return false;
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}
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}
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38
test/Transforms/LoopVectorize/if-conversion-reduction.ll
Normal file
38
test/Transforms/LoopVectorize/if-conversion-reduction.ll
Normal file
@ -0,0 +1,38 @@
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; RUN: opt < %s -loop-vectorize -force-vector-width=4 -enable-if-conversion -dce -instcombine -licm -S | FileCheck %s
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target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
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target triple = "x86_64-apple-macosx10.9.0"
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;CHECK: @reduction_func
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;CHECK-NOT: load <4 x i32>
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;CHECK: ret i32
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define i32 @reduction_func(i32* nocapture %A, i32 %n) nounwind uwtable readonly ssp {
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entry:
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%cmp10 = icmp sgt i32 %n, 0
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br i1 %cmp10, label %for.body, label %for.end
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for.body: ; preds = %entry, %for.inc
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%indvars.iv = phi i64 [ %indvars.iv.next, %for.inc ], [ 0, %entry ]
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%sum.011 = phi i32 [ %sum.1, %for.inc ], [ 0, %entry ]
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%arrayidx = getelementptr inbounds i32* %A, i64 %indvars.iv
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%0 = load i32* %arrayidx, align 4
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%cmp1 = icmp sgt i32 %0, 30
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br i1 %cmp1, label %if.then, label %for.inc
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if.then: ; preds = %for.body
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%add = add i32 %sum.011, 2
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%add4 = add i32 %add, %0
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br label %for.inc
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for.inc: ; preds = %for.body, %if.then
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%sum.1 = phi i32 [ %add4, %if.then ], [ %sum.011, %for.body ]
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%indvars.iv.next = add i64 %indvars.iv, 1
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%lftr.wideiv = trunc i64 %indvars.iv.next to i32
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%exitcond = icmp eq i32 %lftr.wideiv, %n
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br i1 %exitcond, label %for.end, label %for.body
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for.end: ; preds = %for.inc, %entry
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%sum.0.lcssa = phi i32 [ 0, %entry ], [ 4, %for.inc ]
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ret i32 %sum.0.lcssa
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}
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