Put a heuristic in place to prevent GVN from falling into bad cases with massively complicated CFGs.
This speeds up a particular testcase from 12+ hours to 5 seconds with little perceptible loss of quality.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@55391 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp
index 272ad1b..42fbc78 100644
--- a/lib/Transforms/Scalar/GVN.cpp
+++ b/lib/Transforms/Scalar/GVN.cpp
@@ -862,6 +862,12 @@
DenseMap<BasicBlock*, Value*> deps;
MD.getNonLocalDependency(L, deps);
+ // If we had to process more than one hundred blocks to find the
+ // dependencies, this load isn't worth worrying about. Optimizing
+ // it will be too expensive.
+ if (deps.size() > 100)
+ return false;
+
DenseMap<BasicBlock*, Value*> repl;
// Filter out useless results (non-locals, etc)