[llvm] r197449 - LoopVectorizer: Don't if-convert constant expressions that can trap
Arnold Schwaighofer
aschwaighofer at apple.com
Mon Dec 16 17:11:01 PST 2013
Author: arnolds
Date: Mon Dec 16 19:11:01 2013
New Revision: 197449
URL: http://llvm.org/viewvc/llvm-project?rev=197449&view=rev
Log:
LoopVectorizer: Don't if-convert constant expressions that can trap
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
Modified:
llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp
llvm/trunk/test/Transforms/LoopVectorize/if-conversion.ll
Modified: llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp?rev=197449&r1=197448&r2=197449&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp (original)
+++ llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp Mon Dec 16 19:11:01 2013
@@ -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::canVecto
}
// 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::canVecto
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::blockCan
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;
Modified: llvm/trunk/test/Transforms/LoopVectorize/if-conversion.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopVectorize/if-conversion.ll?rev=197449&r1=197448&r2=197449&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LoopVectorize/if-conversion.ll (original)
+++ llvm/trunk/test/Transforms/LoopVectorize/if-conversion.ll Mon Dec 16 19:11:01 2013
@@ -106,3 +106,66 @@ for.end:
ret i32 %sum.0.lcssa
}
+ at a = common global [1 x i32*] zeroinitializer, align 8
+ at 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
+}
More information about the llvm-commits
mailing list