[SimplifyCFG] Be more aggressive

Up the phi node folding threshold from a cheap "1" to a meagre "2".

Update tests for extra added selects and slight code churn.

llvm-svn: 229099

1 files changed, 6 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index b65fd38b836..6717be15db9 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -53,9 +53,13 @@ using namespace PatternMatch;
 
 #define DEBUG_TYPE "simplifycfg"
 
+// Chosen as 2 so as to be cheap, but still to have enough power to fold
+// a select, so the "clamp" idiom (of a min followed by a max) will be caught.
+// To catch this, we need to fold a compare and a select, hence '2' being the
+// minimum reasonable default.
 static cl::opt<unsigned>
-PHINodeFoldingThreshold("phi-node-folding-threshold", cl::Hidden, cl::init(1),
-   cl::desc("Control the amount of phi node folding to perform (default = 1)"));
+PHINodeFoldingThreshold("phi-node-folding-threshold", cl::Hidden, cl::init(2),
+   cl::desc("Control the amount of phi node folding to perform (default = 2)"));
 
 static cl::opt<bool>
 DupRet("simplifycfg-dup-ret", cl::Hidden, cl::init(false),