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change simplifycfg to not duplicate 'unwind' instructions. Hopefully

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this will increase the likelihood of common code getting sunk towards
the unwind.

llvm-svn: 83996
This commit is contained in:
Chris Lattner 2009-10-13 18:13:05 +00:00
parent f5049b6bb8
commit 26c670aa44
2 changed files with 23 additions and 15 deletions
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17
lib/Transforms/Utils/SimplifyCFG.cpp
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@ -1860,33 +1860,26 @@ bool llvm::SimplifyCFG(BasicBlock *BB) {
} else if (isa<UnwindInst>(BB->begin())) {
// Check to see if the first instruction in this block is just an unwind.
// If so, replace any invoke instructions which use this as an exception
// destination with call instructions, and any unconditional branch
// predecessor with an unwind.
// destination with call instructions.
//
SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
while (!Preds.empty()) {
BasicBlock *Pred = Preds.back();
if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator())) {
if (BI->isUnconditional()) {
Pred->getInstList().pop_back(); // nuke uncond branch
new UnwindInst(Pred->getContext(), Pred); // Use unwind.
Changed = true;
}
} else if (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator()))
if (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator()))
if (II->getUnwindDest() == BB) {
// Insert a new branch instruction before the invoke, because this
// is now a fall through...
// is now a fall through.
BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
Pred->getInstList().remove(II); // Take out of symbol table
// Insert the call now...
// Insert the call now.
SmallVector<Value*,8> Args(II->op_begin()+3, II->op_end());
CallInst *CI = CallInst::Create(II->getCalledValue(),
Args.begin(), Args.end(),
II->getName(), BI);
CI->setCallingConv(II->getCallingConv());
CI->setAttributes(II->getAttributes());
// If the invoke produced a value, the Call now does instead
// If the invoke produced a value, the Call now does instead.
II->replaceAllUsesWith(CI);
delete II;
Changed = true;

21
test/Transforms/SimplifyCFG/invoke_unwind.ll
View File

@ -1,10 +1,9 @@
; This testcase checks to see if the simplifycfg pass is converting invoke
; instructions to call instructions if the handler just rethrows the exception.
; RUN: opt < %s -simplifycfg -S | FileCheck %s
declare void @bar()
; This testcase checks to see if the simplifycfg pass is converting invoke
; instructions to call instructions if the handler just rethrows the exception.
define i32 @test1() {
; CHECK: @test1
; CHECK-NEXT: call void @bar()
@ -16,3 +15,19 @@ Ok: ; preds = %0
Rethrow: ; preds = %0
unwind
}
; Verify that simplifycfg isn't duplicating 'unwind' instructions. Doing this
; is bad because it discourages commoning.
define i32 @test2(i1 %c) {
; CHECK: @test2
; CHECK: T:
; CHECK-NEXT: call void @bar()
; CHECK-NEXT: br label %F
br i1 %c, label %T, label %F
T:
call void @bar()
br label %F
F:
unwind
}