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TRE: Just erase dead BBs and tweak the iteration loop not to increment the deleted BB iterator.

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Leaving empty blocks around just opens up a can of bugs like PR22704. Deleting
them early also slightly simplifies code.

Thanks to Sanjay for the IR test case.

llvm-svn: 230856
This commit is contained in:
Benjamin Kramer 2015-02-28 16:47:27 +00:00
parent 4d39ffa2aa
commit 1a8767d1c0
2 changed files with 28 additions and 19 deletions
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26
lib/Transforms/Scalar/TailRecursionElimination.cpp
View File

@ -403,28 +403,19 @@ bool TailCallElim::runTRE(Function &F) {
// alloca' is changed from being a static alloca to being a dynamic alloca.
// Until this is resolved, disable this transformation if that would ever
// happen. This bug is PR962.
SmallVector<BasicBlock*, 8> BBToErase;
for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
for (Function::iterator BBI = F.begin(), E = F.end(); BBI != E; /*in loop*/) {
BasicBlock *BB = BBI++; // FoldReturnAndProcessPred may delete BB.
if (ReturnInst *Ret = dyn_cast<ReturnInst>(BB->getTerminator())) {
bool Change = ProcessReturningBlock(Ret, OldEntry, TailCallsAreMarkedTail,
ArgumentPHIs, !CanTRETailMarkedCall);
if (!Change && BB->getFirstNonPHIOrDbg() == Ret) {
if (!Change && BB->getFirstNonPHIOrDbg() == Ret)
Change = FoldReturnAndProcessPred(BB, Ret, OldEntry,
TailCallsAreMarkedTail, ArgumentPHIs,
!CanTRETailMarkedCall);
// FoldReturnAndProcessPred may have emptied some BB. Remember to
// erase them.
if (Change && BB->empty())
BBToErase.push_back(BB);
}
MadeChange |= Change;
}
}
for (auto BB: BBToErase)
BB->eraseFromParent();
// If we eliminated any tail recursions, it's possible that we inserted some
// silly PHI nodes which just merge an initial value (the incoming operand)
// with themselves. Check to see if we did and clean up our mess if so. This
@ -831,14 +822,11 @@ bool TailCallElim::FoldReturnAndProcessPred(BasicBlock *BB,
ReturnInst *RI = FoldReturnIntoUncondBranch(Ret, BB, Pred);
// Cleanup: if all predecessors of BB have been eliminated by
// FoldReturnIntoUncondBranch, we would like to delete it, but we
// can not just nuke it as it is being used as an iterator by our caller.
// Just empty it, and the caller will erase it when it is safe to do so.
// It is important to empty it, because the ret instruction in there is
// still using a value which EliminateRecursiveTailCall will attempt
// to remove.
// FoldReturnIntoUncondBranch, delete it. It is important to empty it,
// because the ret instruction in there is still using a value which
// EliminateRecursiveTailCall will attempt to remove.
if (!BB->hasAddressTaken() && pred_begin(BB) == pred_end(BB))
BB->getInstList().clear();
BB->eraseFromParent();
EliminateRecursiveTailCall(CI, RI, OldEntry, TailCallsAreMarkedTail,
ArgumentPHIs,

21
test/Transforms/TailCallElim/inf-recursion.ll
View File

@ -31,3 +31,24 @@ define float @fabsf(float %f) {
}
declare x86_fp80 @fabsl(x86_fp80 %f)
; Don't crash while transforming a function with infinite recursion.
define i32 @PR22704(i1 %bool) {
entry:
br i1 %bool, label %t, label %f
t:
%call1 = call i32 @PR22704(i1 1)
br label %return
f:
%call = call i32 @PR22704(i1 1)
br label %return
return:
ret i32 0
; CHECK-LABEL: @PR22704(
; CHECK: %bool.tr = phi i1 [ %bool, %entry ], [ true, %t ], [ true, %f ]
; CHECK: br i1 %bool.tr, label %t, label %f
}