Don't hoist things out of a large switch inside a
loop, for the reasons in the comments. This is a
major win on 253.perlbmk on ARM Darwin. I expect it
to be a good heuristic in general, but it's possible
some things will regress; I'll be watching.
7940152.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@108792 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/MachineLICM.cpp b/lib/CodeGen/MachineLICM.cpp
index 4c054f5..83f66ce 100644
--- a/lib/CodeGen/MachineLICM.cpp
+++ b/lib/CodeGen/MachineLICM.cpp
@@ -489,8 +489,12 @@
}
const std::vector<MachineDomTreeNode*> &Children = N->getChildren();
- for (unsigned I = 0, E = Children.size(); I != E; ++I)
- HoistRegion(Children[I]);
+ // Don't hoist things out of a large switch statement. This often causes
+ // code to be hoisted that wasn't going to be executed, and increases
+ // register pressure in a situation where it's likely to matter.
+ if (Children.size() < 10)
+ for (unsigned I = 0, E = Children.size(); I != E; ++I)
+ HoistRegion(Children[I]);
}
/// IsLICMCandidate - Returns true if the instruction may be a suitable