GVN: Fix quadratic runtime on the number of switch cases.
No intended behavior change. This was introduced in r162023. With the fixed
algorithm a Release build of ARMInstPrinter.cpp goes from 16s to 10s on a
2011 MBP.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@162559 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp
index 4822fd0..3a89623 100644
--- a/lib/Transforms/Scalar/GVN.cpp
+++ b/lib/Transforms/Scalar/GVN.cpp
@@ -2231,12 +2231,20 @@
Value *SwitchCond = SI->getCondition();
BasicBlock *Parent = SI->getParent();
bool Changed = false;
+
+ // Remember how many outgoing edges there are to every successor.
+ SmallDenseMap<BasicBlock *, unsigned, 16> SwitchEdges;
+ for (unsigned i = 0, n = SI->getNumSuccessors(); i != n; ++i)
+ ++SwitchEdges[SI->getSuccessor(i)];
+
for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
i != e; ++i) {
BasicBlock *Dst = i.getCaseSuccessor();
- BasicBlockEdge E(Parent, Dst);
- if (E.isSingleEdge())
+ // If there is only a single edge, propagate the case value into it.
+ if (SwitchEdges.lookup(Dst) == 1) {
+ BasicBlockEdge E(Parent, Dst);
Changed |= propagateEquality(SwitchCond, i.getCaseValue(), E);
+ }
}
return Changed;
}