SimplifyCFG: Omit range checks for switch lookup tables when default is unreachable
They would get optimized away later, but we might as well not emit them.
llvm-svn: 223051
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 48d6a81..91127b2 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -4134,19 +4134,20 @@
"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 fully 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.
+ // If the default destination is unreachable, or if the lookup table covers
+ // all values of the conditional variable, branch directly to the lookup table
+ // BB. Otherwise, check that the condition is within the case range.
+ const bool DefaultIsReachable =
+ !isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg());
+ const bool GeneratingCoveredLookupTable = (MaxTableSize == TableSize);
BranchInst *RangeCheckBranch = nullptr;
- const bool GeneratingCoveredLookupTable = MaxTableSize == TableSize;
- if (GeneratingCoveredLookupTable) {
+ if (!DefaultIsReachable || GeneratingCoveredLookupTable) {
Builder.CreateBr(LookupBB);
// We cached PHINodes in PHIs, to avoid accessing deleted PHINodes later,
// do not delete PHINodes here.
SI->getDefaultDest()->removePredecessor(SI->getParent(),
- true/*DontDeleteUselessPHIs*/);
+ true /*DontDeleteUselessPHIs*/);
} else {
Value *Cmp = Builder.CreateICmpULT(TableIndex, ConstantInt::get(
MinCaseVal->getType(), TableSize));