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[LoopPeeling] Fix condition for phi-eliminating peeling

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When peeling loops basing on phis becoming invariants, we make a wrong loop size check.
UP.Threshold should be compared against the total numbers of instructions after the transformation,
which is equal to 2 * LoopSize in case of peeling one iteration.
We should also check that the maximum allowed number of peeled iterations is not zero.

Reviewers: sanjoy, anna, reames, mkuper

Reviewed By: mkuper

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D31753

llvm-svn: 300441
This commit is contained in:
Max Kazantsev 2017-04-17 05:38:28 +00:00
parent 4c27f4ad1e
commit 2198626e48
3 changed files with 31 additions and 2 deletions
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3
lib/Transforms/Utils/LoopUnrollPeel.cpp
View File

@ -82,7 +82,8 @@ void llvm::computePeelCount(Loop *L, unsigned LoopSize,
// its only back edge. If there is such Phi, peeling 1 iteration from the
// loop is profitable, because starting from 2nd iteration we will have an
// invariant instead of this Phi.
if (LoopSize <= UP.Threshold) {
// First, check that we can peel at least one iteration.
if (2 * LoopSize <= UP.Threshold && UnrollPeelMaxCount > 0) {
BasicBlock *BackEdge = L->getLoopLatch();
assert(BackEdge && "Loop is not in simplified form?");
BasicBlock *Header = L->getHeader();

28
test/Transforms/LoopUnroll/peel-loop-negative.ll Normal file
View File

@ -0,0 +1,28 @@
; RUN: opt < %s -S -loop-unroll -unroll-threshold=800 -unroll-peel-max-count=0 | FileCheck %s
; We should not peel this loop even though we can, because the max count is set
; to zero.
define i32 @invariant_backedge_neg_1(i32 %a, i32 %b) {
; CHECK-LABEL: @invariant_backedge_neg_1
; CHECK-NOT loop.peel{{.*}}:
; CHECK: loop:
; CHECK: %i = phi
; CHECK: %sum = phi
; CHECK: %plus = phi
entry:
br label %loop
loop:
%i = phi i32 [ 0, %entry ], [ %inc, %loop ]
%sum = phi i32 [ 0, %entry ], [ %incsum, %loop ]
%plus = phi i32 [ %a, %entry ], [ %b, %loop ]
%incsum = add i32 %sum, %plus
%inc = add i32 %i, 1
%cmp = icmp slt i32 %i, 1000
br i1 %cmp, label %loop, label %exit
exit:
ret i32 %sum
}

2
test/Transforms/LoopUnroll/peel-loop-not-forced.ll
View File

@ -1,4 +1,4 @@
; RUN: opt < %s -S -loop-unroll -unroll-threshold=4 | FileCheck %s
; RUN: opt < %s -S -loop-unroll -unroll-threshold=8 | FileCheck %s
define i32 @invariant_backedge_1(i32 %a, i32 %b) {
; CHECK-LABEL: @invariant_backedge_1