Teach SimplifyCFG that (switch (select cond, X, Y)) is better expressed as a branch.
Based on a patch by Alistair Lynn.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@126647 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index c670885..72fa468 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -1800,6 +1800,26 @@
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 @@
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();