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[SimplifyCFG] Don't fold conditional branches that contain calls to convergent functions.

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Summary:
Performing this optimization duplicates the call to the convergent
function and adds new control-flow dependencies, which is a no-no.

Reviewers: jingyue

Subscribers: broune, hfinkel, tra, resistor, joker.eph, arsenm, llvm-commits, mzolotukhin

Differential Revision: http://reviews.llvm.org/D17128

llvm-svn: 260730
This commit is contained in:
Justin Lebar 2016-02-12 21:01:36 +00:00
parent 9fd0bc5568
commit b60c46619b
2 changed files with 34 additions and 14 deletions
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20
lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -1690,19 +1690,6 @@ static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB,
return true;
}
/// \returns True if this block contains a CallInst with the NoDuplicate
/// attribute.
static bool HasNoDuplicateCall(const BasicBlock *BB) {
for (BasicBlock::const_iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
const CallInst *CI = dyn_cast<CallInst>(I);
if (!CI)
continue;
if (CI->cannotDuplicate())
return true;
}
return false;
}
/// Return true if we can thread a branch across this block.
static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
BranchInst *BI = cast<BranchInst>(BB->getTerminator());
@ -1747,7 +1734,12 @@ static bool FoldCondBranchOnPHI(BranchInst *BI, const DataLayout &DL) {
// Now we know that this block has multiple preds and two succs.
if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
if (HasNoDuplicateCall(BB)) return false;
// Can't fold blocks that contain noduplicate or convergent calls.
if (llvm::any_of(*BB, [](const Instruction &I) {
const CallInst *CI = dyn_cast<CallInst>(&I);
return CI && (CI->cannotDuplicate() || CI->isConvergent());
}))
return false;
// Okay, this is a simple enough basic block. See if any phi values are
// constants.

28
test/Transforms/SimplifyCFG/attr-convergent.ll Normal file
View File

@ -0,0 +1,28 @@
; RUN: opt < %s -simplifycfg -S | FileCheck %s
; Checks that the SimplifyCFG pass won't duplicate a call to a function marked
; convergent.
;
; CHECK: call void @barrier
; CHECK-NOT: call void @barrier
define void @check(i1 %cond, i32* %out) {
entry:
br i1 %cond, label %if.then, label %if.end
if.then:
store i32 5, i32* %out
br label %if.end
if.end:
%x = phi i1 [ true, %entry ], [ false, %if.then ]
call void @barrier()
br i1 %x, label %cond.end, label %cond.false
cond.false:
br label %cond.end
cond.end:
ret void
}
declare void @barrier() convergent