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Fix a bug in vectorization of if-converted reduction variables. If the

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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
This commit is contained in:
Nadav Rotem 2012-12-04 22:40:22 +00:00
parent f7999fe1cb
commit e570dee4b0
2 changed files with 61 additions and 17 deletions
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40
lib/Transforms/Vectorize/LoopVectorize.cpp
View File

@ -1985,20 +1985,20 @@ bool LoopVectorizationLegality::AddReductionVar(PHINode *Phi,
// Also, we can't have multiple block-local users.
Instruction *Iter = Phi;
while (true) {
// Any reduction instr must be of one of the allowed kinds.
if (!isReductionInstr(Iter, Kind))
return false;
// Did we found a user inside this block ?
bool FoundInBlockUser = false;
// Did we reach the initial PHI node ?
bool FoundStartPHI = false;
// If the instruction has no users then this is a broken
// chain and can't be a reduction variable.
if (Iter->use_empty())
return false;
// Any reduction instr must be of one of the allowed kinds.
if (!isReductionInstr(Iter, Kind))
return false;
// Did we find a user inside this block ?
bool FoundInBlockUser = false;
// Did we reach the initial PHI node ?
bool FoundStartPHI = false;
// For each of the *users* of iter.
for (Value::use_iterator it = Iter->use_begin(), e = Iter->use_end();
it != e; ++it) {
@ -2009,21 +2009,22 @@ bool LoopVectorizationLegality::AddReductionVar(PHINode *Phi,
continue;
}
// We allow in-loop PHINodes which are not the original reduction PHI
// node. If this PHI is the only user of Iter (happens in IF w/ no ELSE
// structure) then don't skip this PHI.
if (isa<PHINode>(U) && U->getParent() != TheLoop->getHeader() &&
TheLoop->contains(U->getParent()) && Iter->getNumUses() > 1)
continue;
// Check if we found the exit user.
BasicBlock *Parent = U->getParent();
if (!TheLoop->contains(Parent)) {
// We must have a single exit instruction.
// Exit if you find multiple outside users.
if (ExitInstruction != 0)
return false;
ExitInstruction = Iter;
}
// We allow in-loop PHINodes which are not the original reduction PHI
// node. If this PHI is the only user of Iter (happens in IF w/ no ELSE
// structure) then don't skip this PHI.
if (isa<PHINode>(U) && U->getParent() != TheLoop->getHeader() &&
TheLoop->contains(U) && Iter->getNumUses() > 1)
continue;
// We can't have multiple inside users.
if (FoundInBlockUser)
return false;
@ -2043,6 +2044,11 @@ bool LoopVectorizationLegality::AddReductionVar(PHINode *Phi,
Reductions[Phi] = RD;
return true;
}
// If we've reached the start PHI but did not find an outside user then
// this is dead code. Abort.
if (FoundStartPHI)
return false;
}
}

38
test/Transforms/LoopVectorize/if-conversion-reduction.ll Normal file
View File

@ -0,0 +1,38 @@
; RUN: opt < %s -loop-vectorize -force-vector-width=4 -enable-if-conversion -dce -instcombine -licm -S | FileCheck %s
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"
target triple = "x86_64-apple-macosx10.9.0"
;CHECK: @reduction_func
;CHECK-NOT: load <4 x i32>
;CHECK: ret i32
define i32 @reduction_func(i32* nocapture %A, i32 %n) nounwind uwtable readonly ssp {
entry:
%cmp10 = icmp sgt i32 %n, 0
br i1 %cmp10, label %for.body, label %for.end
for.body: ; preds = %entry, %for.inc
%indvars.iv = phi i64 [ %indvars.iv.next, %for.inc ], [ 0, %entry ]
%sum.011 = phi i32 [ %sum.1, %for.inc ], [ 0, %entry ]
%arrayidx = getelementptr inbounds i32* %A, i64 %indvars.iv
%0 = load i32* %arrayidx, align 4
%cmp1 = icmp sgt i32 %0, 30
br i1 %cmp1, label %if.then, label %for.inc
if.then: ; preds = %for.body
%add = add i32 %sum.011, 2
%add4 = add i32 %add, %0
br label %for.inc
for.inc: ; preds = %for.body, %if.then
%sum.1 = phi i32 [ %add4, %if.then ], [ %sum.011, %for.body ]
%indvars.iv.next = add i64 %indvars.iv, 1
%lftr.wideiv = trunc i64 %indvars.iv.next to i32
%exitcond = icmp eq i32 %lftr.wideiv, %n
br i1 %exitcond, label %for.end, label %for.body
for.end: ; preds = %for.inc, %entry
%sum.0.lcssa = phi i32 [ 0, %entry ], [ 4, %for.inc ]
ret i32 %sum.0.lcssa
}