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Teach SimplifyCFG that (switch (select cond, X, Y)) is better expressed as a branch.

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Based on a patch by Alistair Lynn.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@126647 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Frits van Bommel
2011-02-28 09:44:07 +00:00
parent da834093b7
commit f7b2a9d7df
2 changed files with 164 additions and 1 deletions
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27
lib/Transforms/Utils/SimplifyCFG.cpp
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@@ -1800,6 +1800,26 @@ static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond,
return true;
}
// SimplifySwitchOnSelect - Replaces
// (switch (select cond, X, Y)) on constant X, Y
// with a branch - conditional if X and Y lead to distinct BBs,
// unconditional otherwise.
static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) {
// Check for constant integer values in the select.
ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue());
ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue());
if (!TrueVal || !FalseVal)
return false;
// Find the relevant condition and destinations.
Value *Condition = Select->getCondition();
BasicBlock *TrueBB = SI->getSuccessor(SI->findCaseValue(TrueVal));
BasicBlock *FalseBB = SI->getSuccessor(SI->findCaseValue(FalseVal));
// Perform the actual simplification.
return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB);
}
// SimplifyIndirectBrOnSelect - Replaces
// (indirectbr (select cond, blockaddress(@fn, BlockA),
// blockaddress(@fn, BlockB)))
@@ -2309,7 +2329,12 @@ bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI) {
if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
return SimplifyCFG(BB) | true;
Value *Cond = SI->getCondition();
if (SelectInst *Select = dyn_cast<SelectInst>(Cond))
if (SimplifySwitchOnSelect(SI, Select))
return SimplifyCFG(BB) | true;
// If the block only contains the switch, see if we can fold the block
// away into any preds.
BasicBlock::iterator BBI = BB->begin();