[llvm] r358297 - [KnownBits] Add computeForAddCarry()
Nikita Popov via llvm-commits
llvm-commits at lists.llvm.org
Fri Apr 12 11:18:08 PDT 2019
Author: nikic
Date: Fri Apr 12 11:18:08 2019
New Revision: 358297
URL: http://llvm.org/viewvc/llvm-project?rev=358297&view=rev
Log:
[KnownBits] Add computeForAddCarry()
This is for D60460. computeForAddSub() essentially already supports
carries because it has to deal with subtractions. This revision
extracts a lower-level computeForAddCarry() function, which allows
computing the known bits for add (carry known zero), sub (carry known
one) and addcarry (carry unknown).
As we don't seem to have any yet, I've added a unit test file for
KnownBits and exhaustive tests for the new computeForAddCarry()
functionality, as well the existing computeForAddSub() function.
Differential Revision: https://reviews.llvm.org/D60522
Added:
llvm/trunk/unittests/Support/KnownBitsTest.cpp
Modified:
llvm/trunk/include/llvm/Support/KnownBits.h
llvm/trunk/lib/Support/KnownBits.cpp
llvm/trunk/unittests/Support/CMakeLists.txt
Modified: llvm/trunk/include/llvm/Support/KnownBits.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/KnownBits.h?rev=358297&r1=358296&r2=358297&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Support/KnownBits.h (original)
+++ llvm/trunk/include/llvm/Support/KnownBits.h Fri Apr 12 11:18:08 2019
@@ -202,6 +202,10 @@ public:
return getBitWidth() - Zero.countPopulation();
}
+ /// Compute known bits resulting from adding LHS, RHS and a 1-bit Carry.
+ static KnownBits computeForAddCarry(
+ const KnownBits &LHS, const KnownBits &RHS, const KnownBits &Carry);
+
/// Compute known bits resulting from adding LHS and RHS.
static KnownBits computeForAddSub(bool Add, bool NSW, const KnownBits &LHS,
KnownBits RHS);
Modified: llvm/trunk/lib/Support/KnownBits.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/KnownBits.cpp?rev=358297&r1=358296&r2=358297&view=diff
==============================================================================
--- llvm/trunk/lib/Support/KnownBits.cpp (original)
+++ llvm/trunk/lib/Support/KnownBits.cpp Fri Apr 12 11:18:08 2019
@@ -15,18 +15,14 @@
using namespace llvm;
-KnownBits KnownBits::computeForAddSub(bool Add, bool NSW,
- const KnownBits &LHS, KnownBits RHS) {
- // Carry in a 1 for a subtract, rather than 0.
- bool CarryIn = false;
- if (!Add) {
- // Sum = LHS + ~RHS + 1
- std::swap(RHS.Zero, RHS.One);
- CarryIn = true;
- }
+static KnownBits computeForAddCarry(
+ const KnownBits &LHS, const KnownBits &RHS,
+ bool CarryZero, bool CarryOne) {
+ assert(!(CarryZero && CarryOne) &&
+ "Carry can't be zero and one at the same time");
- APInt PossibleSumZero = ~LHS.Zero + ~RHS.Zero + CarryIn;
- APInt PossibleSumOne = LHS.One + RHS.One + CarryIn;
+ APInt PossibleSumZero = ~LHS.Zero + ~RHS.Zero + !CarryZero;
+ APInt PossibleSumOne = LHS.One + RHS.One + CarryOne;
// Compute known bits of the carry.
APInt CarryKnownZero = ~(PossibleSumZero ^ LHS.Zero ^ RHS.Zero);
@@ -45,9 +41,32 @@ KnownBits KnownBits::computeForAddSub(bo
KnownBits KnownOut;
KnownOut.Zero = ~std::move(PossibleSumZero) & Known;
KnownOut.One = std::move(PossibleSumOne) & Known;
+ return KnownOut;
+}
+
+KnownBits KnownBits::computeForAddCarry(
+ const KnownBits &LHS, const KnownBits &RHS, const KnownBits &Carry) {
+ assert(Carry.getBitWidth() == 1 && "Carry must be 1-bit");
+ return ::computeForAddCarry(
+ LHS, RHS, Carry.Zero.getBoolValue(), Carry.One.getBoolValue());
+}
+
+KnownBits KnownBits::computeForAddSub(bool Add, bool NSW,
+ const KnownBits &LHS, KnownBits RHS) {
+ KnownBits KnownOut;
+ if (Add) {
+ // Sum = LHS + RHS + 0
+ KnownOut = ::computeForAddCarry(
+ LHS, RHS, /*CarryZero*/true, /*CarryOne*/false);
+ } else {
+ // Sum = LHS + ~RHS + 1
+ std::swap(RHS.Zero, RHS.One);
+ KnownOut = ::computeForAddCarry(
+ LHS, RHS, /*CarryZero*/false, /*CarryOne*/true);
+ }
// Are we still trying to solve for the sign bit?
- if (!Known.isSignBitSet()) {
+ if (!KnownOut.isNegative() && !KnownOut.isNonNegative()) {
if (NSW) {
// Adding two non-negative numbers, or subtracting a negative number from
// a non-negative one, can't wrap into negative.
Modified: llvm/trunk/unittests/Support/CMakeLists.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/Support/CMakeLists.txt?rev=358297&r1=358296&r2=358297&view=diff
==============================================================================
--- llvm/trunk/unittests/Support/CMakeLists.txt (original)
+++ llvm/trunk/unittests/Support/CMakeLists.txt Fri Apr 12 11:18:08 2019
@@ -34,6 +34,7 @@ add_llvm_unittest(SupportTests
Host.cpp
ItaniumManglingCanonicalizerTest.cpp
JSONTest.cpp
+ KnownBitsTest.cpp
LEB128Test.cpp
LineIteratorTest.cpp
LockFileManagerTest.cpp
Added: llvm/trunk/unittests/Support/KnownBitsTest.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/Support/KnownBitsTest.cpp?rev=358297&view=auto
==============================================================================
--- llvm/trunk/unittests/Support/KnownBitsTest.cpp (added)
+++ llvm/trunk/unittests/Support/KnownBitsTest.cpp Fri Apr 12 11:18:08 2019
@@ -0,0 +1,130 @@
+//===- llvm/unittest/Support/KnownBitsTest.cpp - KnownBits tests ----------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements unit tests for KnownBits functions.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/KnownBits.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+namespace {
+
+template<typename FnTy>
+void ForeachKnownBits(unsigned Bits, FnTy Fn) {
+ unsigned Max = 1 << Bits;
+ KnownBits Known(Bits);
+ for (unsigned Zero = 0; Zero < Max; ++Zero) {
+ for (unsigned One = 0; One < Max; ++One) {
+ Known.Zero = Zero;
+ Known.One = One;
+ if (Known.hasConflict())
+ continue;
+
+ Fn(Known);
+ }
+ }
+}
+
+template<typename FnTy>
+void ForeachNumInKnownBits(const KnownBits &Known, FnTy Fn) {
+ unsigned Bits = Known.getBitWidth();
+ unsigned Max = 1 << Bits;
+ for (unsigned N = 0; N < Max; ++N) {
+ APInt Num(Bits, N);
+ if ((Num & Known.Zero) != 0 || (~Num & Known.One) != 0)
+ continue;
+
+ Fn(Num);
+ }
+}
+
+TEST(KnownBitsTest, AddCarryExhaustive) {
+ unsigned Bits = 4;
+ ForeachKnownBits(Bits, [&](const KnownBits &Known1) {
+ ForeachKnownBits(Bits, [&](const KnownBits &Known2) {
+ ForeachKnownBits(1, [&](const KnownBits &KnownCarry) {
+ // Explicitly compute known bits of the addition by trying all
+ // possibilities.
+ KnownBits Known(Bits);
+ Known.Zero.setAllBits();
+ Known.One.setAllBits();
+ ForeachNumInKnownBits(Known1, [&](const APInt &N1) {
+ ForeachNumInKnownBits(Known2, [&](const APInt &N2) {
+ ForeachNumInKnownBits(KnownCarry, [&](const APInt &Carry) {
+ APInt Add = N1 + N2;
+ if (Carry.getBoolValue())
+ ++Add;
+
+ Known.One &= Add;
+ Known.Zero &= ~Add;
+ });
+ });
+ });
+
+ KnownBits KnownComputed = KnownBits::computeForAddCarry(
+ Known1, Known2, KnownCarry);
+ EXPECT_EQ(Known.Zero, KnownComputed.Zero);
+ EXPECT_EQ(Known.One, KnownComputed.One);
+ });
+ });
+ });
+}
+
+static void TestAddSubExhaustive(bool IsAdd) {
+ unsigned Bits = 4;
+ ForeachKnownBits(Bits, [&](const KnownBits &Known1) {
+ ForeachKnownBits(Bits, [&](const KnownBits &Known2) {
+ KnownBits Known(Bits), KnownNSW(Bits);
+ Known.Zero.setAllBits();
+ Known.One.setAllBits();
+ KnownNSW.Zero.setAllBits();
+ KnownNSW.One.setAllBits();
+
+ ForeachNumInKnownBits(Known1, [&](const APInt &N1) {
+ ForeachNumInKnownBits(Known2, [&](const APInt &N2) {
+ bool Overflow;
+ APInt Res;
+ if (IsAdd)
+ Res = N1.sadd_ov(N2, Overflow);
+ else
+ Res = N1.ssub_ov(N2, Overflow);
+
+ Known.One &= Res;
+ Known.Zero &= ~Res;
+
+ if (!Overflow) {
+ KnownNSW.One &= Res;
+ KnownNSW.Zero &= ~Res;
+ }
+ });
+ });
+
+ KnownBits KnownComputed = KnownBits::computeForAddSub(
+ IsAdd, /*NSW*/false, Known1, Known2);
+ EXPECT_EQ(Known.Zero, KnownComputed.Zero);
+ EXPECT_EQ(Known.One, KnownComputed.One);
+
+ // The NSW calculation is not precise, only check that it's
+ // conservatively correct.
+ KnownBits KnownNSWComputed = KnownBits::computeForAddSub(
+ IsAdd, /*NSW*/true, Known1, Known2);
+ EXPECT_TRUE(KnownNSWComputed.Zero.isSubsetOf(KnownNSW.Zero));
+ EXPECT_TRUE(KnownNSWComputed.One.isSubsetOf(KnownNSW.One));
+ });
+ });
+}
+
+TEST(KnownBitsTest, AddSubExhaustive) {
+ TestAddSubExhaustive(true);
+ TestAddSubExhaustive(false);
+}
+
+} // end anonymous namespace
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