SimplifyCFG: Expose phi node folding cost threshold as command line parameter

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@130528 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index e0125f7b3379675e9d5ac3aca94d4d3989b400fb..18b857308e34ede93d4b7921282c83fcec8e1d4a 100644 (file)
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -37,6 +37,10 @@
 #include <map>
 using namespace llvm;
 
+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)"));
+
 static cl::opt<bool>
 DupRet("simplifycfg-dup-ret", cl::Hidden, cl::init(false),
        cl::desc("Duplicate return instructions into unconditional branches"));
@@ -1246,7 +1250,8 @@ static bool FoldTwoEntryPHINode(PHINode *PN, const TargetData *TD) {
   // instructions.  While we are at it, keep track of the instructions
   // that need to be moved to the dominating block.
   SmallPtrSet<Instruction*, 4> AggressiveInsts;
-  unsigned MaxCostVal0 = 1, MaxCostVal1 = 1;
+  unsigned MaxCostVal0 = PHINodeFoldingThreshold,
+           MaxCostVal1 = PHINodeFoldingThreshold;
   
   for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
     PHINode *PN = cast<PHINode>(II++);

diff --git a/test/Transforms/SimplifyCFG/PhiEliminate3.ll b/test/Transforms/SimplifyCFG/PhiEliminate3.ll
new file mode 100644 (file)
index 0000000..3566b87
--- /dev/null
+++ b/test/Transforms/SimplifyCFG/PhiEliminate3.ll
@@ -0,0 +1,34 @@
+; Test merging of blocks containing complex expressions,
+; with various folding thresholds
+;
+; RUN: opt < %s -simplifycfg -S -phi-node-folding-threshold=1 | grep N:
+; RUN: opt < %s -simplifycfg -S -phi-node-folding-threshold=2 | not grep N:
+; RUN: opt < %s -simplifycfg -S -phi-node-folding-threshold=2 | grep M:
+; RUN: opt < %s -simplifycfg -S -phi-node-folding-threshold=7 | not grep M:
+;
+
+define i32 @test(i1 %a, i1 %b, i32 %i, i32 %j, i32 %k) {
+entry:
+        br i1 %a, label %M, label %O
+O:
+        br i1 %b, label %P, label %Q
+P:
+        %iaj = add i32 %i, %j
+        %iajak = add i32 %iaj, %k
+        br label %N
+Q:
+        %ixj = xor i32 %i, %j
+        %ixjxk = xor i32 %ixj, %k
+        br label %N
+N:
+        ; This phi should be foldable if threshold >= 2
+        %Wp = phi i32 [ %iajak, %P ], [ %ixjxk, %Q ]
+        %Wp2 = add i32 %Wp, %Wp
+        br label %M
+M:
+        ; This phi should be foldable if threshold >= 7
+        %W = phi i32 [ %Wp2, %N ], [ 2, %entry ]
+        %R = add i32 %W, 1
+        ret i32 %R
+}
+