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Fix logic to determine whether to turn a switch into a lookup table. When

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the tables cannot fit in registers (i.e. bitmap), do not emit the table
if it's using an illegal type.

rdar://12779436


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@168970 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng
2012-11-30 02:02:42 +00:00
parent a4eff77e37
commit 40eef5fe36
2 changed files with 39 additions and 6 deletions
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lib/Transforms/Utils/SimplifyCFG.cpp
+13 -6
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@@ -3511,22 +3511,29 @@ bool SwitchLookupTable::WouldFitInRegister(const DataLayout *TD,
static bool ShouldBuildLookupTable(SwitchInst *SI,
uint64_t TableSize,
const DataLayout *TD,
const TargetTransformInfo *TTI,
const SmallDenseMap<PHINode*, Type*>& ResultTypes) {
// The table density should be at least 40%. This is the same criterion as for
// jump tables, see SelectionDAGBuilder::handleJTSwitchCase.
// FIXME: Find the best cut-off.
if (SI->getNumCases() > TableSize || TableSize >= UINT64_MAX / 10)
return false; // TableSize overflowed, or mul below might overflow.
if (SI->getNumCases() * 10 >= TableSize * 4)
return true;
// If each table would fit in a register, we should build it anyway.
bool AllFit = true;
bool HasIllegalType = false;
for (SmallDenseMap<PHINode*, Type*>::const_iterator I = ResultTypes.begin(),
E = ResultTypes.end(); I != E; ++I) {
if (!SwitchLookupTable::WouldFitInRegister(TD, TableSize, I->second))
return false;
Type *Ty = I->second;
if (!TTI->getScalarTargetTransformInfo()->isTypeLegal(Ty))
HasIllegalType = true;
if (!SwitchLookupTable::WouldFitInRegister(TD, TableSize, Ty)) {
AllFit = false;
break;
}
}
return true;
return AllFit || (!HasIllegalType && (SI->getNumCases() * 10 >= TableSize * 4));
}
/// SwitchToLookupTable - If the switch is only used to initialize one or more
@@ -3607,7 +3614,7 @@ static bool SwitchToLookupTable(SwitchInst *SI,
APInt RangeSpread = MaxCaseVal->getValue() - MinCaseVal->getValue();
uint64_t TableSize = RangeSpread.getLimitedValue() + 1;
if (!ShouldBuildLookupTable(SI, TableSize, TD, ResultTypes))
if (!ShouldBuildLookupTable(SI, TableSize, TD, TTI, ResultTypes))
return false;
// Create the BB that does the lookups.