diff --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp index cbec13c7808be..a46edc0b75f54 100644 --- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp +++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp @@ -1301,6 +1301,23 @@ AliasResult BasicAAResult::aliasGEP( if (Range1.intersectWith(Range2).isEmptySet()) return AliasResult::NoAlias; + // Check if abs(V*Scale) >= abs(Scale) holds in the presence of + // potentially wrapping math. + auto MultiplyByScaleNoWrap = [](const VariableGEPIndex &Var) { + if (Var.IsNSW) + return true; + + int ValOrigBW = Var.Val.V->getType()->getPrimitiveSizeInBits(); + // If Scale is small enough so that abs(V*Scale) >= abs(Scale) holds. + // The max value of abs(V) is 2^ValOrigBW - 1. Multiplying with a + // constant smaller than 2^(bitwidth(Val) - ValOrigBW) won't wrap. + int MaxScaleValueBW = Var.Val.getBitWidth() - ValOrigBW; + if (MaxScaleValueBW <= 0) + return false; + return Var.Scale.ule( + APInt::getMaxValue(MaxScaleValueBW).zext(Var.Scale.getBitWidth())); + }; + // Try to determine the range of values for VarIndex such that // VarIndex <= -MinAbsVarIndex || MinAbsVarIndex <= VarIndex. std::optional MinAbsVarIndex; @@ -1309,22 +1326,6 @@ AliasResult BasicAAResult::aliasGEP( const VariableGEPIndex &Var = DecompGEP1.VarIndices[0]; if (Var.Val.TruncBits == 0 && isKnownNonZero(Var.Val.V, SimplifyQuery(DL, DT, &AC, Var.CxtI))) { - // Check if abs(V*Scale) >= abs(Scale) holds in the presence of - // potentially wrapping math. - auto MultiplyByScaleNoWrap = [](const VariableGEPIndex &Var) { - if (Var.IsNSW) - return true; - - int ValOrigBW = Var.Val.V->getType()->getPrimitiveSizeInBits(); - // If Scale is small enough so that abs(V*Scale) >= abs(Scale) holds. - // The max value of abs(V) is 2^ValOrigBW - 1. Multiplying with a - // constant smaller than 2^(bitwidth(Val) - ValOrigBW) won't wrap. - int MaxScaleValueBW = Var.Val.getBitWidth() - ValOrigBW; - if (MaxScaleValueBW <= 0) - return false; - return Var.Scale.ule( - APInt::getMaxValue(MaxScaleValueBW).zext(Var.Scale.getBitWidth())); - }; // Refine MinAbsVarIndex, if abs(Scale*V) >= abs(Scale) holds in the // presence of potentially wrapping math. if (MultiplyByScaleNoWrap(Var)) { @@ -1341,6 +1342,7 @@ AliasResult BasicAAResult::aliasGEP( const VariableGEPIndex &Var1 = DecompGEP1.VarIndices[1]; if (Var0.hasNegatedScaleOf(Var1) && Var0.Val.TruncBits == 0 && Var0.Val.hasSameCastsAs(Var1.Val) && !AAQI.MayBeCrossIteration && + MultiplyByScaleNoWrap(Var0) && MultiplyByScaleNoWrap(Var1) && isKnownNonEqual(Var0.Val.V, Var1.Val.V, SimplifyQuery(DL, DT, &AC, /*CxtI=*/Var0.CxtI ? Var0.CxtI diff --git a/llvm/test/Analysis/BasicAA/gep-modulo.ll b/llvm/test/Analysis/BasicAA/gep-modulo.ll index 159aaf94039d3..9ca69b2d7bbdd 100644 --- a/llvm/test/Analysis/BasicAA/gep-modulo.ll +++ b/llvm/test/Analysis/BasicAA/gep-modulo.ll @@ -393,3 +393,17 @@ entry: } declare void @llvm.assume(i1) + +define i64 @mul_may_overflow_var_nonzero_minabsvarindex_two_index(i64 %arg, ptr %arg1) { +; CHECK-LABEL: Function: mul_may_overflow_var_nonzero_minabsvarindex_two_index +; CHECK-LABEL: MayAlias: i64* %getelementptr, i64* %getelementptr2 +bb: + %xor = xor i64 %arg, -9223372036854775808 + %getelementptr = getelementptr i64, ptr %arg1, i64 %xor + %load = load i64, ptr %getelementptr, align 8 + %getelementptr2 = getelementptr i64, ptr %arg1, i64 %arg + store i64 1, ptr %getelementptr2, align 8 + %load3 = load i64, ptr %getelementptr, align 8 + %mul = mul i64 %load, %load3 + ret i64 %mul +}