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[LoopUtils, LV] Fix PR27246 (first-order recurrences)

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This patch ensures that when we detect first-order recurrences, we reject a phi
node if its previous value is also a phi node. During vectorization the initial
and previous values of the recurrence are shuffled together to create the value
for the current iteration. However, phi nodes are not widened like other
instructions. This fixes PR27246.

Differential Revision: http://reviews.llvm.org/D18971

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@265983 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Matthew Simpson 2016-04-11 19:48:18 +00:00
parent e09329d549
commit 09e9ded8a1
2 changed files with 42 additions and 1 deletions
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2
lib/Transforms/Utils/LoopUtils.cpp
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@ -541,7 +541,7 @@ bool RecurrenceDescriptor::isFirstOrderRecurrence(PHINode *Phi, Loop *TheLoop,
// Get the previous value. The previous value comes from the latch edge while
// the initial value comes form the preheader edge.
auto *Previous = dyn_cast<Instruction>(Phi->getIncomingValueForBlock(Latch));
if (!Previous || !TheLoop->contains(Previous))
if (!Previous || !TheLoop->contains(Previous) || isa<PHINode>(Previous))
return false;
// Ensure every user of the phi node is dominated by the previous value. The

41
test/Transforms/LoopVectorize/AArch64/first-order-recurrence.ll
View File

@ -256,3 +256,44 @@ for.cond.for.end_crit_edge:
for.end:
ret void
}
; CHECK-LABEL: @PR27246
;
; int PR27246() {
; unsigned int e, n;
; for (int i = 1; i < 49; ++i) {
; for (int k = i; k > 1; --k)
; e = k;
; n = e;
; }
; return n;
; }
;
; CHECK-NOT: vector.ph:
;
define i32 @PR27246() {
entry:
br label %for.cond1.preheader
for.cond1.preheader:
%i.016 = phi i32 [ 1, %entry ], [ %inc, %for.cond.cleanup3 ]
%e.015 = phi i32 [ undef, %entry ], [ %e.1.lcssa, %for.cond.cleanup3 ]
br label %for.cond1
for.cond.cleanup:
%e.1.lcssa.lcssa = phi i32 [ %e.1.lcssa, %for.cond.cleanup3 ]
ret i32 %e.1.lcssa.lcssa
for.cond1:
%e.1 = phi i32 [ %k.0, %for.cond1 ], [ %e.015, %for.cond1.preheader ]
%k.0 = phi i32 [ %dec, %for.cond1 ], [ %i.016, %for.cond1.preheader ]
%cmp2 = icmp sgt i32 %k.0, 1
%dec = add nsw i32 %k.0, -1
br i1 %cmp2, label %for.cond1, label %for.cond.cleanup3
for.cond.cleanup3:
%e.1.lcssa = phi i32 [ %e.1, %for.cond1 ]
%inc = add nuw nsw i32 %i.016, 1
%exitcond = icmp eq i32 %inc, 49
br i1 %exitcond, label %for.cond.cleanup, label %for.cond1.preheader
}