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SimplifyCFG: fix a bug in switch to table conversion

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We use gep to access the global array "switch.table", and the table index
should be treated as unsigned. When the highest bit is 1, this commit
zero-extends the index to an integer type with larger size.

For a switch on i2, we used to generate:
%switch.tableidx = sub i2 %0, -2
getelementptr inbounds [4 x i64]* @switch.table, i32 0, i2 %switch.tableidx

It is incorrect when %switch.tableidx is 2 or 3. The fix is to generate
%switch.tableidx = sub i2 %0, -2
%switch.tableidx.zext = zext i2 %switch.tableidx to i3
getelementptr inbounds [4 x i64]* @switch.table, i32 0, i3 %switch.tableidx.zext

rdar://17735071


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213815 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Manman Ren
2014-07-23 23:13:23 +00:00
parent 48b8c128df
commit 4cae9cb034
2 changed files with 54 additions and 4 deletions
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17
lib/Transforms/Utils/SimplifyCFG.cpp
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@ -3477,7 +3477,7 @@ namespace {
/// BuildLookup - Build instructions with Builder to retrieve the value at
/// the position given by Index in the lookup table.
Value *BuildLookup(Value *Index, IRBuilder<> &Builder);
Value *BuildLookup(Value *Index, uint64_t TableSize, IRBuilder<> &Builder);
/// WouldFitInRegister - Return true if a table with TableSize elements of
/// type ElementType would fit in a target-legal register.
@ -3598,7 +3598,8 @@ SwitchLookupTable::SwitchLookupTable(Module &M,
Kind = ArrayKind;
}
Value *SwitchLookupTable::BuildLookup(Value *Index, IRBuilder<> &Builder) {
Value *SwitchLookupTable::BuildLookup(Value *Index, uint64_t TableSize,
IRBuilder<> &Builder) {
switch (Kind) {
case SingleValueKind:
return SingleValue;
@ -3624,6 +3625,14 @@ Value *SwitchLookupTable::BuildLookup(Value *Index, IRBuilder<> &Builder) {
"switch.masked");
}
case ArrayKind: {
// Make sure the table index will not overflow when treated as signed.
if (IntegerType *IT = dyn_cast<IntegerType>(Index->getType()))
if (TableSize > (1 << (IT->getBitWidth() - 1)))
Index = Builder.CreateZExt(Index,
IntegerType::get(IT->getContext(),
IT->getBitWidth() + 1),
"switch.tableidx.zext");
Value *GEPIndices[] = { Builder.getInt32(0), Index };
Value *GEP = Builder.CreateInBoundsGEP(Array, GEPIndices,
"switch.gep");
@ -3823,7 +3832,7 @@ static bool SwitchToLookupTable(SwitchInst *SI,
SI->getDefaultDest()->removePredecessor(SI->getParent());
} else {
Value *Cmp = Builder.CreateICmpULT(TableIndex, ConstantInt::get(
MinCaseVal->getType(), TableSize));
MinCaseVal->getType(), TableSize));
Builder.CreateCondBr(Cmp, LookupBB, SI->getDefaultDest());
}
@ -3878,7 +3887,7 @@ static bool SwitchToLookupTable(SwitchInst *SI,
SwitchLookupTable Table(Mod, TableSize, MinCaseVal, ResultLists[PHI],
DV, DL);
Value *Result = Table.BuildLookup(TableIndex, Builder);
Value *Result = Table.BuildLookup(TableIndex, TableSize, Builder);
// If the result is used to return immediately from the function, we want to
// do that right here.