[PATCH] D157807: [ValueTracking] Strengthen analysis in `computeKnownBits` of phi

[Noah Goldstein via Phabricator via llvm-commits]

goldstein.w.n updated this revision to Diff 549724.
goldstein.w.n added a comment.

Remove extra depth


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D157807/new/

https://reviews.llvm.org/D157807

Files:
  llvm/lib/Analysis/ValueTracking.cpp
  llvm/test/Analysis/ScalarEvolution/outer_phi.ll


Index: llvm/test/Analysis/ScalarEvolution/outer_phi.ll
===================================================================
--- llvm/test/Analysis/ScalarEvolution/outer_phi.ll
+++ llvm/test/Analysis/ScalarEvolution/outer_phi.ll
@@ -7,7 +7,7 @@
 ; CHECK-LABEL: 'test_01'
 ; CHECK-NEXT:  Classifying expressions for: @test_01
 ; CHECK-NEXT:    %outer.iv = phi i32 [ 0, %entry ], [ %iv.next, %outer.backedge ]
-; CHECK-NEXT:    --> %outer.iv U: [0,-2147483647) S: [0,-2147483647) Exits: <<Unknown>> LoopDispositions: { %outer: Variant, %inner: Invariant }
+; CHECK-NEXT:    --> %outer.iv U: [0,-2147483648) S: [0,-2147483648) Exits: <<Unknown>> LoopDispositions: { %outer: Variant, %inner: Invariant }
 ; CHECK-NEXT:    %iv = phi i32 [ 0, %outer ], [ %iv.next, %inner.backedge ]
 ; CHECK-NEXT:    --> {0,+,1}<nuw><nsw><%inner> U: [0,-2147483648) S: [0,-2147483648) Exits: <<Unknown>> LoopDispositions: { %inner: Computable, %outer: Variant }
 ; CHECK-NEXT:    %iv.next = add nuw nsw i32 %iv, 1
Index: llvm/lib/Analysis/ValueTracking.cpp
===================================================================
--- llvm/lib/Analysis/ValueTracking.cpp
+++ llvm/lib/Analysis/ValueTracking.cpp
@@ -1459,11 +1459,13 @@
 
         // Recurse, but cap the recursion to one level, because we don't
         // want to waste time spinning around in loops.
+        // TODO: See if we can base recursion limitter on number of incoming phi
+        // edges so we don't overly clamp analysis.
         computeKnownBits(IncValue, Known2, MaxAnalysisRecursionDepth - 1, RecQ);
 
-        // If this failed, see if we can use a conditional branch into the phi
+        // See if we can further use a conditional branch into the phi
         // to help us determine the range of the value.
-        if (Known2.isUnknown()) {
+        if (!Known2.isConstant()) {
           ICmpInst::Predicate Pred;
           const APInt *RHSC;
           BasicBlock *TrueSucc, *FalseSucc;
@@ -1478,7 +1480,7 @@
                 Pred = CmpInst::getInversePredicate(Pred);
               // Get the knownbits implied by the incoming phi condition.
               auto CR = ConstantRange::makeExactICmpRegion(Pred, *RHSC);
-              Known2 = CR.toKnownBits();
+              Known2 = Known2.unionWith(CR.toKnownBits());
             }
           }
         }


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