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SimplifyCFG: Do not transform PHI to select if doing so would be unsafe 

PR16069 is an interesting case where an incoming value to a PHI is a
trap value while also being a 'ConstantExpr'.

We do not consider this case when performing the 'HoistThenElseCodeToIf'
optimization.

Instead, make our modifications more conservative if we detect that we
cannot transform the PHI to a select.

llvm-svn: 183152
This commit is contained in:
David Majnemer 2013-06-03 20:43:12 +00:00
parent 8e7dd2f628
commit c82f27af2a
2 changed files with 33 additions and 2 deletions
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21
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -1081,9 +1081,9 @@ static bool HoistThenElseCodeToIf(BranchInst *BI) {
(isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
return false;
// If we get here, we can hoist at least one instruction.
BasicBlock *BIParent = BI->getParent();
bool Changed = false;
do {
// If we are hoisting the terminator instruction, don't move one (making a
// broken BB), instead clone it, and remove BI.
@ -1098,6 +1098,7 @@ static bool HoistThenElseCodeToIf(BranchInst *BI) {
I2->replaceAllUsesWith(I1);
I1->intersectOptionalDataWith(I2);
I2->eraseFromParent();
Changed = true;
I1 = BB1_Itr++;
I2 = BB2_Itr++;
@ -1117,7 +1118,23 @@ static bool HoistThenElseCodeToIf(BranchInst *BI) {
HoistTerminator:
// It may not be possible to hoist an invoke.
if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
return true;
return Changed;
for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
PHINode *PN;
for (BasicBlock::iterator BBI = SI->begin();
(PN = dyn_cast<PHINode>(BBI)); ++BBI) {
Value *BB1V = PN->getIncomingValueForBlock(BB1);
Value *BB2V = PN->getIncomingValueForBlock(BB2);
if (BB1V == BB2V)
continue;
if (isa<ConstantExpr>(BB1V) && !isSafeToSpeculativelyExecute(BB1V))
return Changed;
if (isa<ConstantExpr>(BB2V) && !isSafeToSpeculativelyExecute(BB2V))
return Changed;
}
}
// Okay, it is safe to hoist the terminator.
Instruction *NT = I1->clone();

14
llvm/test/Transforms/SimplifyCFG/PR16069.ll Normal file
View File

@ -0,0 +1,14 @@
; RUN: opt < %s -simplifycfg -S | FileCheck %s
; CHECK-NOT: select
@b = extern_weak global i32
define i32 @foo(i1 %y) {
br i1 %y, label %bb1, label %bb2
bb1:
br label %bb3
bb2:
br label %bb3
bb3:
%cond.i = phi i32 [ 0, %bb1 ], [ srem (i32 1, i32 zext (i1 icmp eq (i32* @b, i32* null) to i32)), %bb2 ]
ret i32 %cond.i
}