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[SimplifyCFG] Merge together cleanuppads

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Cleanuppads may be merged together if one is the only predecessor of the
other in which case a simple transform can be performed: replace the
a cleanupret with a branch and remove an unnecessary cleanuppad.

Differential Revision: http://reviews.llvm.org/D17459

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@261390 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer 2016-02-20 01:07:45 +00:00
parent 7ed6f01c5d
commit 1f296bf0b8
2 changed files with 84 additions and 2 deletions
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47
lib/Transforms/Utils/SimplifyCFG.cpp
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@ -3371,7 +3371,7 @@ bool SimplifyCFGOpt::SimplifySingleResume(ResumeInst *RI) {
return true;
}
bool SimplifyCFGOpt::SimplifyCleanupReturn(CleanupReturnInst *RI) {
static bool removeEmptyCleanup(CleanupReturnInst *RI) {
// If this is a trivial cleanup pad that executes no instructions, it can be
// eliminated. If the cleanup pad continues to the caller, any predecessor
// that is an EH pad will be updated to continue to the caller and any
@ -3489,6 +3489,49 @@ bool SimplifyCFGOpt::SimplifyCleanupReturn(CleanupReturnInst *RI) {
return true;
}
// Try to merge two cleanuppads together.
static bool mergeCleanupPad(CleanupReturnInst *RI) {
// Skip any cleanuprets which unwind to caller, there is nothing to merge
// with.
BasicBlock *UnwindDest = RI->getUnwindDest();
if (!UnwindDest)
return false;
// This cleanupret isn't the only predecessor of this cleanuppad, it wouldn't
// be safe to merge without code duplication.
if (UnwindDest->getSinglePredecessor() != RI->getParent())
return false;
// Verify that our cleanuppad's unwind destination is another cleanuppad.
auto *SuccessorCleanupPad = dyn_cast<CleanupPadInst>(&UnwindDest->front());
if (!SuccessorCleanupPad)
return false;
CleanupPadInst *PredecessorCleanupPad = RI->getCleanupPad();
// Replace any uses of the successor cleanupad with the predecessor pad
// The only cleanuppad uses should be this cleanupret, it's cleanupret and
// funclet bundle operands.
SuccessorCleanupPad->replaceAllUsesWith(PredecessorCleanupPad);
// Remove the old cleanuppad.
SuccessorCleanupPad->eraseFromParent();
// Now, we simply replace the cleanupret with a branch to the unwind
// destination.
BranchInst::Create(UnwindDest, RI->getParent());
RI->eraseFromParent();
return true;
}
bool SimplifyCFGOpt::SimplifyCleanupReturn(CleanupReturnInst *RI) {
if (removeEmptyCleanup(RI))
return true;
if (mergeCleanupPad(RI))
return true;
return false;
}
bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder) {
BasicBlock *BB = RI->getParent();
if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
@ -4978,7 +5021,7 @@ static bool TryToMergeLandingPad(LandingPadInst *LPad, BranchInst *BI,
if (!BI2 || !BI2->isIdenticalTo(BI))
continue;
// We've found an identical block. Update our predeccessors to take that
// We've found an identical block. Update our predecessors to take that
// path instead and make ourselves dead.
SmallSet<BasicBlock *, 16> Preds;
Preds.insert(pred_begin(BB), pred_end(BB));

39
test/Transforms/SimplifyCFG/merge-cleanuppads.ll Normal file
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@ -0,0 +1,39 @@
; RUN: opt -S -simplifycfg < %s | FileCheck %s
target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-pc-windows-msvc18.0.0"
; Function Attrs: uwtable
define void @test1() #0 personality i32 (...)* @__CxxFrameHandler3 {
entry:
invoke void @may_throw(i32 3)
to label %invoke.cont unwind label %ehcleanup
invoke.cont: ; preds = %entry
tail call void @may_throw(i32 2) #2
tail call void @may_throw(i32 1) #2
ret void
ehcleanup: ; preds = %entry
%cp = cleanuppad within none []
tail call void @may_throw(i32 2) #2 [ "funclet"(token %cp) ]
cleanupret from %cp unwind label %ehcleanup2
ehcleanup2:
%cp2 = cleanuppad within none []
tail call void @may_throw(i32 1) #2 [ "funclet"(token %cp2) ]
cleanupret from %cp2 unwind to caller
}
; CHECK-LABEL: define void @test1(
; CHECK: %[[cp:.*]] = cleanuppad within none []
; CHECK: tail call void @may_throw(i32 2) #2 [ "funclet"(token %[[cp]]) ]
; CHECK: tail call void @may_throw(i32 1) #2 [ "funclet"(token %[[cp]]) ]
; CHECK: cleanupret from %[[cp]] unwind to caller
declare void @may_throw(i32) #1
declare i32 @__CxxFrameHandler3(...)
attributes #0 = { uwtable "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2" "unsafe-fp-math"="false" "use-soft-float"="false" }
attributes #1 = { "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2" "unsafe-fp-math"="false" "use-soft-float"="false" }
attributes #2 = { nounwind }