Index: llvm/trunk/lib/Analysis/ValueTracking.cpp =================================================================== --- llvm/trunk/lib/Analysis/ValueTracking.cpp +++ llvm/trunk/lib/Analysis/ValueTracking.cpp @@ -1077,6 +1077,22 @@ KnownOne &= KnownOne2; // Output known-0 are known to be clear if zero in either the LHS | RHS. KnownZero |= KnownZero2; + + // and(x, add (x, -1)) is a common idiom that always clears the low bit; + // here we handle the more general case of adding any odd number by + // matching the form add(x, add(x, y)) where y is odd. + // TODO: This could be generalized to clearing any bit set in y where the + // following bit is known to be unset in y. + Value *Y = nullptr; + if (match(I->getOperand(0), m_Add(m_Specific(I->getOperand(1)), + m_Value(Y))) || + match(I->getOperand(1), m_Add(m_Specific(I->getOperand(0)), + m_Value(Y)))) { + APInt KnownZero3(BitWidth, 0), KnownOne3(BitWidth, 0); + computeKnownBits(Y, KnownZero3, KnownOne3, DL, Depth + 1, Q); + if (KnownOne3.countTrailingOnes() > 0) + KnownZero |= APInt::getLowBitsSet(BitWidth, 1); + } break; } case Instruction::Or: { Index: llvm/trunk/test/Transforms/InstSimplify/add-mask.ll =================================================================== --- llvm/trunk/test/Transforms/InstSimplify/add-mask.ll +++ llvm/trunk/test/Transforms/InstSimplify/add-mask.ll @@ -0,0 +1,65 @@ +; RUN: opt -S -instsimplify < %s | FileCheck %s + +define i1 @test(i32 %a) { +; CHECK-LABEL: @test +; CHECK: ret i1 false + %rhs = add i32 %a, -1 + %and = and i32 %a, %rhs + %res = icmp eq i32 %and, 1 + ret i1 %res +} + +define i1 @test2(i32 %a) { +; CHECK-LABEL: @test2 +; CHECK: ret i1 false + %rhs = add i32 %a, 1 + %and = and i32 %a, %rhs + %res = icmp eq i32 %and, 1 + ret i1 %res +} + +define i1 @test3(i32 %a) { +; CHECK-LABEL: @test3 +; CHECK: ret i1 false + %rhs = add i32 %a, 7 + %and = and i32 %a, %rhs + %res = icmp eq i32 %and, 1 + ret i1 %res +} + +@B = external global i32 +declare void @llvm.assume(i1) + +; Known bits without a constant +define i1 @test4(i32 %a) { +; CHECK-LABEL: @test4 +; CHECK: ret i1 false + %b = load i32, i32* @B + %b.and = and i32 %b, 1 + %b.cnd = icmp eq i32 %b.and, 1 + call void @llvm.assume(i1 %b.cnd) + + %rhs = add i32 %a, %b + %and = and i32 %a, %rhs + %res = icmp eq i32 %and, 1 + ret i1 %res +} + +; Negative test - even number +define i1 @test5(i32 %a) { +; CHECK-LABEL: @test5 +; CHECK: ret i1 %res + %rhs = add i32 %a, 2 + %and = and i32 %a, %rhs + %res = icmp eq i32 %and, 1 + ret i1 %res +} + +define i1 @test6(i32 %a) { +; CHECK-LABEL: @test6 +; CHECK: ret i1 false + %lhs = add i32 %a, -1 + %and = and i32 %lhs, %a + %res = icmp eq i32 %and, 1 + ret i1 %res +}