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LoopVectorizer: Fix a dominance issue

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The induction variables start value needs to be defined before we branch
(overflow check) to the scalar preheader where we used it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211460 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Arnold Schwaighofer 2014-06-22 03:38:59 +00:00
parent c815039ca2
commit 78f173a22d
2 changed files with 51 additions and 8 deletions
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25
lib/Transforms/Vectorize/LoopVectorize.cpp
View File

@ -1987,10 +1987,6 @@ void InnerLoopVectorizer::createEmptyLoop() {
Constant::getAllOnesValue(BackedgeCount->getType()),
"backedge.overflow", BypassBlock->getTerminator());
// Count holds the overall loop count (N).
Value *Count = Exp.expandCodeFor(ExitCount, ExitCount->getType(),
BypassBlock->getTerminator());
// The loop index does not have to start at Zero. Find the original start
// value from the induction PHI node. If we don't have an induction variable
// then we know that it starts at zero.
@ -2000,6 +1996,18 @@ void InnerLoopVectorizer::createEmptyLoop() {
IdxTy):
ConstantInt::get(IdxTy, 0);
// We need an instruction to anchor the overflow check on. StartIdx needs to
// be defined before the overflow check branch. Because the scalar preheader
// is going to merge the start index and so the overflow branch block needs to
// contain a definition of the start index.
Instruction *OverflowCheckAnchor = BinaryOperator::CreateAdd(
StartIdx, ConstantInt::get(IdxTy, 0), "overflow.check.anchor",
BypassBlock->getTerminator());
// Count holds the overall loop count (N).
Value *Count = Exp.expandCodeFor(ExitCount, ExitCount->getType(),
BypassBlock->getTerminator());
LoopBypassBlocks.push_back(BypassBlock);
// Split the single block loop into the two loop structure described above.
@ -2068,17 +2076,18 @@ void InnerLoopVectorizer::createEmptyLoop() {
// Now, compare the new count to zero. If it is zero skip the vector loop and
// jump to the scalar loop.
Value *Cmp = BypassBuilder.CreateICmpEQ(IdxEndRoundDown, StartIdx,
"cmp.zero");
Value *Cmp =
BypassBuilder.CreateICmpEQ(IdxEndRoundDown, StartIdx, "cmp.zero");
BasicBlock *LastBypassBlock = BypassBlock;
// Generate code to check that the loops trip count that we computed by adding
// one to the backedge-taken count will not overflow.
{
auto PastOverflowCheck = std::next(BasicBlock::iterator(CheckBCOverflow));
auto PastOverflowCheck =
std::next(BasicBlock::iterator(OverflowCheckAnchor));
BasicBlock *CheckBlock =
LastBypassBlock->splitBasicBlock(PastOverflowCheck, "overflow.checked");
LastBypassBlock->splitBasicBlock(PastOverflowCheck, "overflow.checked");
if (ParentLoop)
ParentLoop->addBasicBlockToLoop(CheckBlock, LI->getBase());
LoopBypassBlocks.push_back(CheckBlock);

34
test/Transforms/LoopVectorize/induction.ll
View File

@ -135,3 +135,37 @@ define i32 @max_i32_backedgetaken() nounwind readnone ssp uwtable {
; <label>:5 ; preds = %1
ret i32 %2
}
; When generating the overflow check we must sure that the induction start value
; is defined before the branch to the scalar preheader.
; CHECK-LABEL: testoverflowcheck
; CHECK: entry
; CHECK: %[[LOAD:.*]] = load i8
; CHECK: %[[VAL:.*]] = zext i8 %[[LOAD]] to i32
; CHECK: br
; CHECK: scalar.ph
; CHECK: phi i32 [ %{{.*}}, %middle.block ], [ %[[VAL]], %entry ]
@e = global i8 1, align 1
@d = common global i32 0, align 4
@c = common global i32 0, align 4
define i32 @testoverflowcheck() {
entry:
%.pr.i = load i8* @e, align 1
%0 = load i32* @d, align 4
%c.promoted.i = load i32* @c, align 4
br label %cond.end.i
cond.end.i:
%inc4.i = phi i8 [ %.pr.i, %entry ], [ %inc.i, %cond.end.i ]
%and3.i = phi i32 [ %c.promoted.i, %entry ], [ %and.i, %cond.end.i ]
%and.i = and i32 %0, %and3.i
%inc.i = add i8 %inc4.i, 1
%tobool.i = icmp eq i8 %inc.i, 0
br i1 %tobool.i, label %loopexit, label %cond.end.i
loopexit:
ret i32 %and.i
}