[llvm-commits] [Review] GVN Patch

[Bill Wendling]

For those of you wondering why I was so interested in dominance, there is a situation where GVN is barfing because it goes into an infinite loop. The problem is that it's trying to process a non-local load which has a dependency in a block that's unreachable from the entry point. It gets into an infinite loop because the GEP it is querying is of this form:

	%xx = getelementptr %some.type %xx ...

which I'm told is perfectly valid within unreachable blocks.

Below (inlined because it's so small) is my fix for this. It at least allows the code to compile to completion. I haven't worked with GVN much before, so I don't know if this has any non-local effects.

Please review this and let me know if it's okay to commit. (And I will commit a testcase with this once it's been approved.)

Thanks.

-bw

diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp
index e67d8af..5411786 100644
--- a/lib/Transforms/Scalar/GVN.cpp
+++ b/lib/Transforms/Scalar/GVN.cpp
@@ -1368,6 +1368,8 @@ bool GVN::processNonLocalLoad(LoadInst *LI) {
     BasicBlock *DepBB = Deps[i].getBB();
     MemDepResult DepInfo = Deps[i].getResult();
 
+    if (!DT->isReachableFromEntry(DepBB)) continue;
+
     if (!DepInfo.isDef() && !DepInfo.isClobber()) {
       UnavailableBlocks.push_back(DepBB);
       continue;