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LoopVectorizer: Don't if-convert constant expressions that can trap

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A phi node operand or an instruction operand could be a constant expression that
can trap (division). Check that we don't vectorize such cases.

PR16729
radar://15653590

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197449 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Arnold Schwaighofer 2013-12-17 01:11:01 +00:00
parent a6380c22e4
commit 83196a9fcb
2 changed files with 94 additions and 1 deletions
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32
lib/Transforms/Vectorize/LoopVectorize.cpp
View File

@ -2804,6 +2804,23 @@ void InnerLoopVectorizer::updateAnalysis() {
DEBUG(DT->verifyAnalysis());
}
/// \brief Check whether it is safe to if-convert this phi node.
///
/// Phi nodes with constant expressions that can trap are not safe to if
/// convert.
static bool canIfConvertPHINodes(BasicBlock *BB) {
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
PHINode *Phi = dyn_cast<PHINode>(I);
if (!Phi)
return true;
for (unsigned p = 0, e = Phi->getNumIncomingValues(); p != e; ++p)
if (Constant *C = dyn_cast<Constant>(Phi->getIncomingValue(p)))
if (C->canTrap())
return false;
}
return true;
}
bool LoopVectorizationLegality::canVectorizeWithIfConvert() {
if (!EnableIfConversion)
return false;
@ -2830,6 +2847,7 @@ bool LoopVectorizationLegality::canVectorizeWithIfConvert() {
}
// Collect the blocks that need predication.
BasicBlock *Header = TheLoop->getHeader();
for (Loop::block_iterator BI = TheLoop->block_begin(),
BE = TheLoop->block_end(); BI != BE; ++BI) {
BasicBlock *BB = *BI;
@ -2839,8 +2857,12 @@ bool LoopVectorizationLegality::canVectorizeWithIfConvert() {
return false;
// We must be able to predicate all blocks that need to be predicated.
if (blockNeedsPredication(BB) && !blockCanBePredicated(BB, SafePointes))
if (blockNeedsPredication(BB)) {
if (!blockCanBePredicated(BB, SafePointes))
return false;
} else if (BB != Header && !canIfConvertPHINodes(BB))
return false;
}
// We can if-convert this loop.
@ -4394,6 +4416,14 @@ bool LoopVectorizationLegality::blockCanBePredicated(BasicBlock *BB,
if (it->mayWriteToMemory() || it->mayThrow())
return false;
// Check that we don't have a constant expression that can trap as operand.
for (Instruction::op_iterator OI = it->op_begin(), OE = it->op_end();
OI != OE; ++OI) {
if (Constant *C = dyn_cast<Constant>(*OI))
if (C->canTrap())
return false;
}
// The instructions below can trap.
switch (it->getOpcode()) {
default: continue;

63
test/Transforms/LoopVectorize/if-conversion.ll
View File

@ -106,3 +106,66 @@ for.end: ; preds = %for.inc, %entry
ret i32 %sum.0.lcssa
}
@a = common global [1 x i32*] zeroinitializer, align 8
@c = common global i32* null, align 8
; We use to if convert this loop. This is not safe because there is a trapping
; constant expression.
; PR16729
; CHECK-LABEL: trapping_constant_expression
; CHECK-NOT: or <4 x i32>
define i32 @trapping_constant_expression() {
entry:
br label %for.body
for.body:
%inc3 = phi i32 [ 0, %entry ], [ %inc, %cond.end ]
%or2 = phi i32 [ 0, %entry ], [ %or, %cond.end ]
br i1 icmp eq (i32** getelementptr inbounds ([1 x i32*]* @a, i64 0, i64 0), i32** @c), label %cond.false, label %cond.end
cond.false:
br label %cond.end
cond.end:
%cond = phi i32 [ sdiv (i32 1, i32 zext (i1 icmp eq (i32** getelementptr inbounds ([1 x i32*]* @a, i64 0, i64 0), i32** @c) to i32)), %cond.false ], [ 0, %for.body ]
%or = or i32 %or2, %cond
%inc = add nsw i32 %inc3, 1
%cmp = icmp slt i32 %inc, 128
br i1 %cmp, label %for.body, label %for.end
for.end:
ret i32 %or
}
; Neither should we if-convert if there is an instruction operand that is a
; trapping constant expression.
; PR16729
; CHECK-LABEL: trapping_constant_expression2
; CHECK-NOT: or <4 x i32>
define i32 @trapping_constant_expression2() {
entry:
br label %for.body
for.body:
%inc3 = phi i32 [ 0, %entry ], [ %inc, %cond.end ]
%or2 = phi i32 [ 0, %entry ], [ %or, %cond.end ]
br i1 icmp eq (i32** getelementptr inbounds ([1 x i32*]* @a, i64 0, i64 0), i32** @c), label %cond.false, label %cond.end
cond.false:
%cond.1 = or i32 %inc3, sdiv (i32 1, i32 zext (i1 icmp eq (i32** getelementptr inbounds ([1 x i32*]* @a, i64 0, i64 0), i32** @c) to i32))
br label %cond.end
cond.end:
%cond = phi i32 [ %cond.1, %cond.false ], [ %inc3, %for.body ]
%or = or i32 %or2, %cond
%inc = add nsw i32 %inc3, 1
%cmp = icmp slt i32 %inc, 128
br i1 %cmp, label %for.body, label %for.end
for.end:
ret i32 %or
}