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

[Noah Goldstein via Phabricator via llvm-commits]

goldstein.w.n updated this revision to Diff 549992.
goldstein.w.n added a comment.

Fixup tests


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/ValueTracking/phi-known-bits.ll


Index: llvm/test/Analysis/ValueTracking/phi-known-bits.ll
===================================================================
--- llvm/test/Analysis/ValueTracking/phi-known-bits.ll
+++ llvm/test/Analysis/ValueTracking/phi-known-bits.ll
@@ -375,13 +375,10 @@
 define i8 @phi_ugt_high_bits_and_known(i8 %xx) {
 ; CHECK-LABEL: @phi_ugt_high_bits_and_known(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[X:%.*]] = or i8 [[XX:%.*]], 1
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt i8 [[X]], -65
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt i8 [[XX:%.*]], -65
 ; CHECK-NEXT:    br i1 [[CMP]], label [[T:%.*]], label [[F:%.*]]
 ; CHECK:       T:
-; CHECK-NEXT:    [[V:%.*]] = phi i8 [ [[X]], [[ENTRY:%.*]] ], [ -1, [[F]] ]
-; CHECK-NEXT:    [[R:%.*]] = and i8 [[V]], 65
-; CHECK-NEXT:    ret i8 [[R]]
+; CHECK-NEXT:    ret i8 65
 ; CHECK:       F:
 ; CHECK-NEXT:    br label [[T]]
 ;
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 limiter 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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