[Mlir-commits] [llvm] [mlir] MathExtras: add overflow query for signed-div (PR #97901)
Ramkumar Ramachandra
llvmlistbot at llvm.org
Sat Jul 6 09:27:55 PDT 2024
https://github.com/artagnon updated https://github.com/llvm/llvm-project/pull/97901
>From f4c879cdd76757a9b9cb0ce7f70bbbd5e03e6350 Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <ramkumar.ramachandra at codasip.com>
Date: Sat, 6 Jul 2024 16:06:58 +0100
Subject: [PATCH 1/2] MathExtras: add overflow query for signed-div
5221634 (Do not trigger UB during AffineExpr parsing) noticed that
divideCeilSigned and divideFloorSigned would overflow when Numerator =
INT_MIN, and Denominator = -1. This observation has already been made by
DynamicAPInt, and it has code to check this. To avoid checks in multiple
callers, centralize this query in MathExtras.
---
llvm/include/llvm/ADT/DynamicAPInt.h | 17 ++++++-----------
llvm/include/llvm/Support/MathExtras.h | 13 +++++++++----
mlir/lib/IR/AffineExpr.cpp | 11 +++--------
3 files changed, 18 insertions(+), 23 deletions(-)
diff --git a/llvm/include/llvm/ADT/DynamicAPInt.h b/llvm/include/llvm/ADT/DynamicAPInt.h
index f312f776df971f..9fe93a60d7653f 100644
--- a/llvm/include/llvm/ADT/DynamicAPInt.h
+++ b/llvm/include/llvm/ADT/DynamicAPInt.h
@@ -231,13 +231,6 @@ LLVM_ATTRIBUTE_ALWAYS_INLINE DynamicAPInt dynamicAPIntFromInt64(int64_t X) {
LLVM_ATTRIBUTE_ALWAYS_INLINE DynamicAPInt mod(const DynamicAPInt &LHS,
const DynamicAPInt &RHS);
-namespace detail {
-// Division overflows only when trying to negate the minimal signed value.
-LLVM_ATTRIBUTE_ALWAYS_INLINE bool divWouldOverflow(int64_t X, int64_t Y) {
- return X == std::numeric_limits<int64_t>::min() && Y == -1;
-}
-} // namespace detail
-
/// We define the operations here in the header to facilitate inlining.
/// ---------------------------------------------------------------------------
@@ -338,7 +331,7 @@ LLVM_ATTRIBUTE_ALWAYS_INLINE DynamicAPInt
DynamicAPInt::operator/(const DynamicAPInt &O) const {
if (LLVM_LIKELY(isSmall() && O.isSmall())) {
// Division overflows only occur when negating the minimal possible value.
- if (LLVM_UNLIKELY(detail::divWouldOverflow(getSmall(), O.getSmall())))
+ if (LLVM_UNLIKELY(divideSignedWouldOverflow(getSmall(), O.getSmall())))
return -*this;
return DynamicAPInt(getSmall() / O.getSmall());
}
@@ -353,7 +346,8 @@ LLVM_ATTRIBUTE_ALWAYS_INLINE DynamicAPInt abs(const DynamicAPInt &X) {
LLVM_ATTRIBUTE_ALWAYS_INLINE DynamicAPInt ceilDiv(const DynamicAPInt &LHS,
const DynamicAPInt &RHS) {
if (LLVM_LIKELY(LHS.isSmall() && RHS.isSmall())) {
- if (LLVM_UNLIKELY(detail::divWouldOverflow(LHS.getSmall(), RHS.getSmall())))
+ if (LLVM_UNLIKELY(
+ divideSignedWouldOverflow(LHS.getSmall(), RHS.getSmall())))
return -LHS;
return DynamicAPInt(divideCeilSigned(LHS.getSmall(), RHS.getSmall()));
}
@@ -363,7 +357,8 @@ LLVM_ATTRIBUTE_ALWAYS_INLINE DynamicAPInt ceilDiv(const DynamicAPInt &LHS,
LLVM_ATTRIBUTE_ALWAYS_INLINE DynamicAPInt floorDiv(const DynamicAPInt &LHS,
const DynamicAPInt &RHS) {
if (LLVM_LIKELY(LHS.isSmall() && RHS.isSmall())) {
- if (LLVM_UNLIKELY(detail::divWouldOverflow(LHS.getSmall(), RHS.getSmall())))
+ if (LLVM_UNLIKELY(
+ divideSignedWouldOverflow(LHS.getSmall(), RHS.getSmall())))
return -LHS;
return DynamicAPInt(divideFloorSigned(LHS.getSmall(), RHS.getSmall()));
}
@@ -473,7 +468,7 @@ LLVM_ATTRIBUTE_ALWAYS_INLINE DynamicAPInt &
DynamicAPInt::operator/=(const DynamicAPInt &O) {
if (LLVM_LIKELY(isSmall() && O.isSmall())) {
// Division overflows only occur when negating the minimal possible value.
- if (LLVM_UNLIKELY(detail::divWouldOverflow(getSmall(), O.getSmall())))
+ if (LLVM_UNLIKELY(divideSignedWouldOverflow(getSmall(), O.getSmall())))
return *this = -*this;
getSmall() /= O.getSmall();
return *this;
diff --git a/llvm/include/llvm/Support/MathExtras.h b/llvm/include/llvm/Support/MathExtras.h
index f6b1fdb6aba9ef..fcc90cb43927fc 100644
--- a/llvm/include/llvm/Support/MathExtras.h
+++ b/llvm/include/llvm/Support/MathExtras.h
@@ -413,9 +413,15 @@ constexpr uint64_t divideCeil(uint64_t Numerator, uint64_t Denominator) {
return (Numerator - Bias) / Denominator + Bias;
}
+// Check whether divideCeilSigned or divideFloorSigned would overflow. This
+// happens only when trying to negate the minimal signed value.
+constexpr bool divideSignedWouldOverflow(int64_t Numerator,
+ int64_t Denominator) {
+ return Numerator == std::numeric_limits<int64_t>::min() && Denominator == -1;
+}
+
/// Returns the integer ceil(Numerator / Denominator). Signed version.
-/// Guaranteed to never overflow, unless Numerator is INT64_MIN and Denominator
-/// is -1.
+/// Overflows when divideSignedWouldOverflow returns true.
template <typename U, typename V, typename T = common_sint<U, V>>
constexpr T divideCeilSigned(U Numerator, V Denominator) {
assert(Denominator && "Division by zero");
@@ -429,8 +435,7 @@ constexpr T divideCeilSigned(U Numerator, V Denominator) {
}
/// Returns the integer floor(Numerator / Denominator). Signed version.
-/// Guaranteed to never overflow, unless Numerator is INT64_MIN and Denominator
-/// is -1.
+/// Overflows when divideSignedWouldOverflow returns true.
template <typename U, typename V, typename T = common_sint<U, V>>
constexpr T divideFloorSigned(U Numerator, V Denominator) {
assert(Denominator && "Division by zero");
diff --git a/mlir/lib/IR/AffineExpr.cpp b/mlir/lib/IR/AffineExpr.cpp
index 798398464da8dd..bfb7c4849356eb 100644
--- a/mlir/lib/IR/AffineExpr.cpp
+++ b/mlir/lib/IR/AffineExpr.cpp
@@ -26,6 +26,7 @@ using namespace mlir::detail;
using llvm::divideCeilSigned;
using llvm::divideFloorSigned;
+using llvm::divideSignedWouldOverflow;
using llvm::mod;
MLIRContext *AffineExpr::getContext() const { return expr->context; }
@@ -859,11 +860,8 @@ static AffineExpr simplifyFloorDiv(AffineExpr lhs, AffineExpr rhs) {
return nullptr;
if (lhsConst) {
- // divideFloorSigned can only overflow in this case:
- if (lhsConst.getValue() == std::numeric_limits<int64_t>::min() &&
- rhsConst.getValue() == -1) {
+ if (divideSignedWouldOverflow(lhsConst.getValue(), rhsConst.getValue()))
return nullptr;
- }
return getAffineConstantExpr(
divideFloorSigned(lhsConst.getValue(), rhsConst.getValue()),
lhs.getContext());
@@ -921,11 +919,8 @@ static AffineExpr simplifyCeilDiv(AffineExpr lhs, AffineExpr rhs) {
return nullptr;
if (lhsConst) {
- // divideCeilSigned can only overflow in this case:
- if (lhsConst.getValue() == std::numeric_limits<int64_t>::min() &&
- rhsConst.getValue() == -1) {
+ if (divideSignedWouldOverflow(lhsConst.getValue(), rhsConst.getValue()))
return nullptr;
- }
return getAffineConstantExpr(
divideCeilSigned(lhsConst.getValue(), rhsConst.getValue()),
lhs.getContext());
>From 18f7148c023d843c5d88f90ef98447c4f3af211d Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <ramkumar.ramachandra at codasip.com>
Date: Sat, 6 Jul 2024 17:11:57 +0100
Subject: [PATCH 2/2] MathExtrasTest: add simple test
---
llvm/unittests/Support/MathExtrasTest.cpp | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/llvm/unittests/Support/MathExtrasTest.cpp b/llvm/unittests/Support/MathExtrasTest.cpp
index a557b61db97520..8053839f86aaeb 100644
--- a/llvm/unittests/Support/MathExtrasTest.cpp
+++ b/llvm/unittests/Support/MathExtrasTest.cpp
@@ -523,6 +523,10 @@ TEST(MathExtras, DivideCeil) {
std::numeric_limits<int64_t>::min() / 2 + 1);
EXPECT_EQ(divideCeilSigned(std::numeric_limits<int64_t>::min(), 1),
std::numeric_limits<int64_t>::min());
+
+ // Overflow.
+ EXPECT_TRUE(
+ divideSignedWouldOverflow(std::numeric_limits<int64_t>::min(), -1));
}
TEST(MathExtras, DivideFloorSigned) {
@@ -544,6 +548,10 @@ TEST(MathExtras, DivideFloorSigned) {
std::numeric_limits<int64_t>::min() / 2);
EXPECT_EQ(divideFloorSigned(std::numeric_limits<int64_t>::min(), 1),
std::numeric_limits<int64_t>::min());
+
+ // Overflow.
+ EXPECT_TRUE(
+ divideSignedWouldOverflow(std::numeric_limits<int64_t>::min(), -1));
}
TEST(MathExtras, Mod) {
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