diff options
Diffstat (limited to 'lib/Transforms/Utils')
-rw-r--r-- | lib/Transforms/Utils/SimplifyCFG.cpp | 34 |
1 files changed, 28 insertions, 6 deletions
diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp index 0e56904ebd..ad3b92a714 100644 --- a/lib/Transforms/Utils/SimplifyCFG.cpp +++ b/lib/Transforms/Utils/SimplifyCFG.cpp @@ -3734,14 +3734,30 @@ static bool SwitchToLookupTable(SwitchInst *SI, CommonDest->getParent(), CommonDest); - // Check whether the condition value is within the case range, and branch to - // the new BB. + // Compute the table index value. Builder.SetInsertPoint(SI); Value *TableIndex = Builder.CreateSub(SI->getCondition(), MinCaseVal, "switch.tableidx"); - Value *Cmp = Builder.CreateICmpULT(TableIndex, ConstantInt::get( - MinCaseVal->getType(), TableSize)); - Builder.CreateCondBr(Cmp, LookupBB, SI->getDefaultDest()); + + // Compute the maximum table size representable by the integer type we are + // switching upon. + const unsigned CaseSize = MinCaseVal->getType()->getPrimitiveSizeInBits(); + const uint64_t MaxTableSize = CaseSize > 63? UINT64_MAX : 1ULL << CaseSize; + assert(MaxTableSize >= TableSize && + "It is impossible for a switch to have more entries than the max " + "representable value of its input integer type's size."); + + // If we have a covered lookup table, unconditionally branch to the lookup table + // BB. Otherwise, check if the condition value is within the case range. If it + // is so, branch to the new BB. Otherwise branch to SI's default destination. + const bool GeneratingCoveredLookupTable = MaxTableSize == TableSize; + if (GeneratingCoveredLookupTable) { + Builder.CreateBr(LookupBB); + } else { + Value *Cmp = Builder.CreateICmpULT(TableIndex, ConstantInt::get( + MinCaseVal->getType(), TableSize)); + Builder.CreateCondBr(Cmp, LookupBB, SI->getDefaultDest()); + } // Populate the BB that does the lookups. Builder.SetInsertPoint(LookupBB); @@ -3772,7 +3788,13 @@ static bool SwitchToLookupTable(SwitchInst *SI, // Remove the switch. for (unsigned i = 0; i < SI->getNumSuccessors(); ++i) { BasicBlock *Succ = SI->getSuccessor(i); - if (Succ == SI->getDefaultDest()) continue; + + // If we are not generating a covered lookup table, we will have a + // conditional branch from SI's parent BB to SI's default destination if our + // input value lies outside of our case range. Thus in that case leave the + // default destination BB as a predecessor of SI's parent BB. + if (Succ == SI->getDefaultDest() && !GeneratingCoveredLookupTable) + continue; Succ->removePredecessor(SI->getParent()); } SI->eraseFromParent(); |