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Do not copy gigantic switch instructions

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@12441 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2004-03-16 19:45:22 +00:00
parent c62db6fc40
commit 4bebf08d15
2 changed files with 19 additions and 2 deletions
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12
lib/Transforms/Scalar/TailDuplication.cpp
View File

@ -91,7 +91,8 @@ bool TailDup::shouldEliminateUnconditionalBranch(TerminatorInst *TI) {
if (Dest == BI->getParent()) return false; // Do not loop infinitely!
// Do not inline a block if we will just get another branch to the same block!
if (BranchInst *DBI = dyn_cast<BranchInst>(Dest->getTerminator()))
TerminatorInst *DTI = Dest->getTerminator();
if (BranchInst *DBI = dyn_cast<BranchInst>(DTI))
if (DBI->isUnconditional() && DBI->getSuccessor(0) == Dest)
return false; // Do not loop infinitely!
@ -110,6 +111,15 @@ bool TailDup::shouldEliminateUnconditionalBranch(TerminatorInst *TI) {
for (unsigned Size = 0; I != Dest->end(); ++Size, ++I)
if (Size == 6) return false; // The block is too large...
// Do not tail duplicate a block that has thousands of successors into a block
// with a single successor if the block has many other predecessors. This can
// cause an N^2 explosion in CFG edges (and PHI node entries), as seen in
// cases that have a large number of indirect gotos.
if (DTI->getNumSuccessors() > 8)
if (std::distance(PI, PE) * DTI->getNumSuccessors() > 128)
return false;
return true;
}

9
lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -331,8 +331,15 @@ static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
// isValueEqualityComparison - Return true if the specified terminator checks to
// see if a value is equal to constant integer value.
static Value *isValueEqualityComparison(TerminatorInst *TI) {
if (SwitchInst *SI = dyn_cast<SwitchInst>(TI))
if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
// Do not permit merging of large switch instructions into their
// predecessors unless there is only one predecessor.
if (SI->getNumSuccessors() * std::distance(pred_begin(SI->getParent()),
pred_end(SI->getParent())) > 128)
return 0;
return SI->getCondition();
}
if (BranchInst *BI = dyn_cast<BranchInst>(TI))
if (BI->isConditional() && BI->getCondition()->hasOneUse())
if (SetCondInst *SCI = dyn_cast<SetCondInst>(BI->getCondition()))