Commit 55637a32 authored by Bill Wendling's avatar Bill Wendling
Browse files

Merging r197449: 

------------------------------------------------------------------------
r197449 | arnolds | 2013-12-16 17:11:01 -0800 (Mon, 16 Dec 2013) | 7 lines

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
------------------------------------------------------------------------

llvm-svn: 197453
parent 4a062ea7

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

+31 −1
Original line number Diff line number Diff line
@@ -2781,6 +2781,23 @@ 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;
@@ -2807,6 +2824,7 @@ 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;
@@ -2816,8 +2834,12 @@ 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.
@@ -4371,6 +4393,14 @@ 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;

llvm/test/Transforms/LoopVectorize/if-conversion.ll

+63 −0
Original line number Diff line number Diff line
@@ -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

}