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LoopVectorizer: A reduction that has multiple uses of the reduction value is not 

a reduction.

Really. Under certain circumstances (the use list of an instruction has to be
set up right - hence the extra pass in the test case) we would not recognize
when a value in a potential reduction cycle was used multiple times by the
reduction cycle.

Fixes PR18526.
radar://15851149

llvm-svn: 199570
This commit is contained in:
Arnold Schwaighofer 2014-01-19 03:18:31 +00:00
parent 043949d446
commit cc742dd9e4
2 changed files with 53 additions and 2 deletions
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13
llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
View File

@ -4535,13 +4535,22 @@ bool LoopVectorizationLegality::AddReductionVar(PHINode *Phi,
continue;
}
// Process instructions only once (termination).
// Process instructions only once (termination). Each reduction cycle
// value must only be used once, except by phi nodes and min/max
// reductions which are represented as a cmp followed by a select.
ReductionInstDesc IgnoredVal(false, 0);
if (VisitedInsts.insert(Usr)) {
if (isa<PHINode>(Usr))
PHIs.push_back(Usr);
else
NonPHIs.push_back(Usr);
}
} else if (!isa<PHINode>(Usr) &&
((!isa<FCmpInst>(Usr) &&
!isa<ICmpInst>(Usr) &&
!isa<SelectInst>(Usr)) ||
!isMinMaxSelectCmpPattern(Usr, IgnoredVal).IsReduction))
return false;
// Remember that we completed the cycle.
if (Usr == Phi)
FoundStartPHI = true;

42
llvm/test/Transforms/LoopVectorize/multi-use-reduction-bug.ll Normal file
View File

@ -0,0 +1,42 @@
; RUN: opt -indvars -loop-vectorize -force-vector-width=2 -force-vector-unroll=1 -S < %s | FileCheck %s
target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-apple-macosx10.9.0"
; We must not vectorize this loop. %add55 is not reduction. Its value is used
; multiple times.
; PR18526
; CHECK: multiple_use_of_value
; CHECK-NOT: <2 x i32>
define void @multiple_use_of_value() {
entry:
%n = alloca i32, align 4
%k7 = alloca i32, align 4
%nf = alloca i32, align 4
%0 = load i32* %k7, align 4
%.neg1 = sub i32 0, %0
%n.promoted = load i32* %n, align 4
%nf.promoted = load i32* %nf, align 4
br label %for.body
for.body:
%inc107 = phi i32 [ undef, %entry ], [ %inc10, %for.body ]
%inc6 = phi i32 [ %nf.promoted, %entry ], [ undef, %for.body ]
%add55 = phi i32 [ %n.promoted, %entry ], [ %add5, %for.body ]
%.neg2 = sub i32 0, %inc6
%add.neg = add i32 0, %add55
%add4.neg = add i32 %add.neg, %.neg1
%sub = add i32 %add4.neg, %.neg2
%add5 = add i32 %sub, %add55
%inc10 = add i32 %inc107, 1
%cmp = icmp ult i32 %inc10, 61
br i1 %cmp, label %for.body, label %for.end
for.end:
%add5.lcssa = phi i32 [ %add5, %for.body ]
store i32 %add5.lcssa, i32* %n, align 4
ret void
}