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[LoopUnrolling] Fix loop size check for peeling

Summary:
We should check if loop size allows us to peel at least one iteration
before we do so.

Patch by Max Kazantsev!

Reviewers: sanjoy, mkuper, efriedma

Reviewed By: mkuper

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D30632

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@297122 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Sanjoy Das 2017-03-07 06:03:15 +00:00
parent fd76e3ca8a
commit cb24f8cc5c
2 changed files with 32 additions and 2 deletions
lib/Transforms/Utils
test/Transforms/LoopUnroll

View File

@ -75,7 +75,9 @@ 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 (auto *BackEdge = L->getLoopLatch()) {
if (LoopSize <= UP.Threshold) {
BasicBlock *BackEdge = L->getLoopLatch();
assert(BackEdge && "Loop is not in simplified form?");
BasicBlock *Header = L->getHeader();
// Iterate over Phis to find one with invariant input on back edge.
bool FoundCandidate = false;

View File

@ -1,4 +1,4 @@
; RUN: opt < %s -S -loop-unroll | FileCheck %s
; RUN: opt < %s -S -loop-unroll -unroll-threshold=4 | FileCheck %s
define i32 @invariant_backedge_1(i32 %a, i32 %b) {
; CHECK-LABEL: @invariant_backedge_1
@ -18,6 +18,34 @@ 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
}
; Peeling should fail due to method size.
define i32 @invariant_backedge_2(i32 %a, i32 %b) {
; CHECK-LABEL: @invariant_backedge_2
; 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 ], [ %incsum2, %loop ]
%plus = phi i32 [ %a, %entry ], [ %b, %loop ]
%incsum = add i32 %sum, %plus
%incsum2 = add i32 %incsum, %plus
%inc = add i32 %i, 1
%cmp = icmp slt i32 %i, 1000
br i1 %cmp, label %loop, label %exit
exit: