[ValueTracking] Compute knownbits for (and/or cond0, cond1) on both sides of branch

The false branch for `and` and true branch for `or` provide less
information (intersection as opposed to union), but still can give
some useful information.

Author: goldsteinn

llvm/lib/Analysis/ValueTracking.cpp

@@ -711,10 +711,17 @@ static void computeKnownBitsFromCond(const Value *V, Value *Cond,
                                      const SimplifyQuery &SQ, bool Invert) {
   Value *A, *B;
   if (Depth < MaxAnalysisRecursionDepth &&
-      (Invert ? match(Cond, m_LogicalOr(m_Value(A), m_Value(B)))
-              : match(Cond, m_LogicalAnd(m_Value(A), m_Value(B))))) {
-    computeKnownBitsFromCond(V, A, Known, Depth + 1, SQ, Invert);
-    computeKnownBitsFromCond(V, B, Known, Depth + 1, SQ, Invert);
+      match(Cond, m_LogicalOp(m_Value(A), m_Value(B)))) {
+    KnownBits Known2(Known.getBitWidth());
+    KnownBits Known3(Known.getBitWidth());
+    computeKnownBitsFromCond(V, A, Known2, Depth + 1, SQ, Invert);
+    computeKnownBitsFromCond(V, B, Known3, Depth + 1, SQ, Invert);
+    if (Invert ? match(Cond, m_LogicalOr(m_Value(A), m_Value(B)))
+               : match(Cond, m_LogicalAnd(m_Value(A), m_Value(B))))
+      Known2 = Known2.unionWith(Known3);
+    else
+      Known2 = Known2.intersectWith(Known3);
+    Known = Known.unionWith(Known2);
   }
 
   if (auto *Cmp = dyn_cast<ICmpInst>(Cond))

llvm/test/Transforms/InstCombine/known-bits.ll

@@ -136,8 +136,7 @@ define i8 @test_cond_and_bothways(i8 %x) {
 ; CHECK-NEXT:    [[OR1:%.*]] = or i8 [[X]], -4
 ; CHECK-NEXT:    ret i8 [[OR1]]
 ; CHECK:       exit:
-; CHECK-NEXT:    [[OR2:%.*]] = or i8 [[X]], -4
-; CHECK-NEXT:    ret i8 [[OR2]]
+; CHECK-NEXT:    ret i8 -4
 ;
   %and = and i8 %x, 91
   %cmp0 = icmp ne i8 %and, 24
@@ -162,8 +161,7 @@ define i8 @test_cond_or_bothways(i8 %x) {
 ; CHECK-NEXT:    [[COND:%.*]] = or i1 [[CMP0]], [[CMP1]]
 ; CHECK-NEXT:    br i1 [[COND]], label [[IF:%.*]], label [[EXIT:%.*]]
 ; CHECK:       if:
-; CHECK-NEXT:    [[OR1:%.*]] = or i8 [[X]], -4
-; CHECK-NEXT:    ret i8 [[OR1]]
+; CHECK-NEXT:    ret i8 -4
 ; CHECK:       exit:
 ; CHECK-NEXT:    [[OR2:%.*]] = or i8 [[X]], -4
 ; CHECK-NEXT:    ret i8 [[OR2]]