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Fix a problem exposed by PR3354: simplifycfg was making a potentially

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trapping instruction be executed unconditionally.

llvm-svn: 62541
This commit is contained in:
Chris Lattner 2009-01-19 23:03:13 +00:00
parent 02b5657666
commit e8fa6f2468
2 changed files with 34 additions and 1 deletions
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15
lib/Transforms/Utils/SimplifyCFG.cpp
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@ -1423,11 +1423,21 @@ static bool FoldBranchToCommonDest(BranchInst *BI) {
if ((!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
Cond->getParent() != BB || &BB->front() != Cond || !Cond->hasOneUse())
return false;
// Make sure the instruction after the condition is the cond branch.
BasicBlock::iterator CondIt = Cond; ++CondIt;
if (&*CondIt != BI)
return false;
// Cond is known to be a compare or binary operator. Check to make sure that
// neither operand is a potentially-trapping constant expression.
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
if (CE->canTrap())
return false;
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
if (CE->canTrap())
return false;
// Finally, don't infinitely unroll conditional loops.
BasicBlock *TrueDest = BI->getSuccessor(0);
@ -1438,6 +1448,7 @@ static bool FoldBranchToCommonDest(BranchInst *BI) {
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
BasicBlock *PredBlock = *PI;
BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
// Check that we have two conditional branches. If there is a PHI node in
// the common successor, verify that the same value flows in from both
// blocks.
@ -1459,6 +1470,8 @@ static bool FoldBranchToCommonDest(BranchInst *BI) {
else
continue;
DOUT << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB;
// If we need to invert the condition in the pred block to match, do so now.
if (InvertPredCond) {
Value *NewCond =

20
test/Transforms/SimplifyCFG/2009-01-19-UnconditionalTrappingConstantExpr.ll Normal file
View File

@ -0,0 +1,20 @@
; RUN: llvm-as < %s | opt -simplifycfg | llvm-dis | grep {br i1 } | count 2
; PR3354
; Do not merge bb1 into the entry block, it might trap.
@G = extern_weak global i32
define i32 @test(i32 %tmp21, i32 %tmp24) {
%tmp25 = icmp sle i32 %tmp21, %tmp24
br i1 %tmp25, label %bb2, label %bb1
bb1: ; preds = %bb
%tmp26 = icmp sgt i32 sdiv (i32 -32768, i32 ptrtoint (i32* @G to i32)), 0
br i1 %tmp26, label %bb6, label %bb2
bb2:
ret i32 42
bb6:
unwind
}