Generalize GVN's conditional propagation logic slightly:
it's OK for the false/true destination to have multiple
predecessors as long as the extra ones are dominated by
the branch destination.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@141176 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp
index f0f16d8..0ad6a8f 100644
--- a/lib/Transforms/Scalar/GVN.cpp
+++ b/lib/Transforms/Scalar/GVN.cpp
@@ -1921,14 +1921,39 @@
BasicBlock *TrueSucc = BI->getSuccessor(0);
BasicBlock *FalseSucc = BI->getSuccessor(1);
-
- if (TrueSucc->getSinglePredecessor())
+ BasicBlock *Parent = BI->getParent();
+
+ // If the true and false branches are to the same basic block then the
+ // branch gives no information about the condition. Eliminating this
+ // here simplifies the rest of the logic.
+ if (TrueSucc == FalseSucc)
+ return false;
+
+ // If the true block can be reached without executing the true edge then we
+ // can't say anything about the value of the condition there.
+ for (pred_iterator PI = pred_begin(TrueSucc), PE = pred_end(TrueSucc);
+ PI != PE; ++PI)
+ if (*PI != Parent && !DT->dominates(TrueSucc, *PI)) {
+ TrueSucc = 0;
+ break;
+ }
+
+ // If the false block can be reached without executing the false edge then
+ // we can't say anything about the value of the condition there.
+ for (pred_iterator PI = pred_begin(FalseSucc), PE = pred_end(FalseSucc);
+ PI != PE; ++PI)
+ if (*PI != Parent && !DT->dominates(FalseSucc, *PI)) {
+ FalseSucc = 0;
+ break;
+ }
+
+ if (TrueSucc)
addToLeaderTable(CondVN,
ConstantInt::getTrue(TrueSucc->getContext()),
TrueSucc);
- if (FalseSucc->getSinglePredecessor())
+ if (FalseSucc)
addToLeaderTable(CondVN,
- ConstantInt::getFalse(TrueSucc->getContext()),
+ ConstantInt::getFalse(FalseSucc->getContext()),
FalseSucc);
return false;