[PATCH] D58113: [SCEV] Teach computeSCEVAtScope benefit from one-input Phi. PR39673

[Philip Reames via Phabricator via llvm-commits]

This revision was not accepted when it landed; it landed in state "Needs Review".
This revision was automatically updated to reflect the committed changes.
Closed by commit rL363180: [SCEV] Teach computeSCEVAtScope benefit from one-input Phi. PR39673 (authored by reames, committed by ).
Herald added a project: LLVM.

Changed prior to commit:
  https://reviews.llvm.org/D58113?vs=186435&id=204323#toc

Repository:
  rL LLVM

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D58113/new/

https://reviews.llvm.org/D58113

Files:
  llvm/trunk/lib/Analysis/ScalarEvolution.cpp
  llvm/trunk/test/Transforms/IndVarSimplify/pr39673.ll


Index: llvm/trunk/test/Transforms/IndVarSimplify/pr39673.ll
===================================================================
--- llvm/trunk/test/Transforms/IndVarSimplify/pr39673.ll
+++ llvm/trunk/test/Transforms/IndVarSimplify/pr39673.ll
@@ -21,8 +21,7 @@
 ; CHECK-NEXT:    [[CMP2:%.*]] = icmp ult i16 [[L2_ADD]], 2
 ; CHECK-NEXT:    br i1 [[CMP2]], label [[LOOP2]], label [[LOOP2_END:%.*]]
 ; CHECK:       loop2.end:
-; CHECK-NEXT:    [[K2_ADD_LCSSA:%.*]] = phi i16 [ [[K2_ADD]], [[LOOP2]] ]
-; CHECK-NEXT:    ret i16 [[K2_ADD_LCSSA]]
+; CHECK-NEXT:    ret i16 184
 ;
 entry:
   br label %loop1
Index: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp
@@ -8138,6 +8138,16 @@
             if (RV) return getSCEV(RV);
           }
         }
+
+        // If there is a single-input Phi, evaluate it at our scope. If we can
+        // prove that this replacement does not break LCSSA form, use new value.
+        if (PN->getNumOperands() == 1) {
+          const SCEV *Input = getSCEV(PN->getOperand(0));
+          const SCEV *InputAtScope = getSCEVAtScope(Input, L);
+          // TODO: We can generalize it using LI.replacementPreservesLCSSAForm,
+          // for the simplest case just support constants.
+          if (isa<SCEVConstant>(InputAtScope)) return InputAtScope;
+        }
       }
 
       // Okay, this is an expression that we cannot symbolically evaluate


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