[SCEV] Recognize simple br-phi patterns

Summary:
Teach SCEV to match patterns like

```
  br %cond, label %left, label %right
 left:
  br label %merge
 right:
  br label %merge
 merge:
  V = phi [ %x, %left ], [ %y, %right ]
```

as "select %cond, %x, %y".  Before this SCEV would match PHI nodes
exclusively to add recurrences.

This addresses PR25005.

Reviewers: joker.eph, joker-eph, atrick

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D13378

llvm-svn: 249211

1 files changed, 8 insertions, 2 deletions

diff --git a/llvm/include/llvm/Analysis/ScalarEvolution.h b/llvm/include/llvm/Analysis/ScalarEvolution.h
index 36e2477528c..c22423b2712 100644
--- a/llvm/include/llvm/Analysis/ScalarEvolution.h
+++ b/llvm/include/llvm/Analysis/ScalarEvolution.h
@@ -415,12 +415,18 @@ namespace llvm {
     /// Provide the special handling we need to analyze PHI SCEVs.
     const SCEV *createNodeForPHI(PHINode *PN);
 
+    /// Helper function called from createNodeForPHI.
+    const SCEV *createAddRecFromPHI(PHINode *PN);
+
+    /// Helper function called from createNodeForPHI.
+    const SCEV *createNodeFromSelectLikePHI(PHINode *PN);
+
     /// Provide special handling for a select-like instruction (currently this
     /// is either a select instruction or a phi node).  \p I is the instruction
     /// being processed, and it is assumed equivalent to "Cond ? TrueVal :
     /// FalseVal".
-    const SCEV *createNodeForSelect(Instruction *I, Value *Cond, Value *TrueVal,
-                                    Value *FalseVal);
+    const SCEV *createNodeForSelectOrPHI(Instruction *I, Value *Cond,
+                                         Value *TrueVal, Value *FalseVal);
 
     /// Provide the special handling we need to analyze GEP SCEVs.
     const SCEV *createNodeForGEP(GEPOperator *GEP);