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[mlir][Support] Avoid multiplication in floorDiv / ceilDiv 

Using comparisons instead avoids potential overflow.

Differential Revision: https://reviews.llvm.org/D116096
This commit is contained in:
Stephan Herhut 2021-12-21 11:31:28 +01:00
parent 55d7a12b86
commit 8761f5ebf7
2 changed files with 8 additions and 2 deletions
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6
mlir/include/mlir/Support/MathExtras.h
View File

@ -24,7 +24,8 @@ inline int64_t ceilDiv(int64_t lhs, int64_t rhs) {
assert(rhs != 0);
// C/C++'s integer division rounds towards 0.
int64_t x = (rhs > 0) ? -1 : 1;
return (lhs * rhs > 0) ? ((lhs + x) / rhs) + 1 : -(-lhs / rhs);
return ((lhs != 0) && (lhs > 0) == (rhs > 0)) ? ((lhs + x) / rhs) + 1
: -(-lhs / rhs);
}
/// Returns the result of MLIR's floordiv operation on constants. The RHS is
@ -33,7 +34,8 @@ inline int64_t floorDiv(int64_t lhs, int64_t rhs) {
assert(rhs != 0);
// C/C++'s integer division rounds towards 0.
int64_t x = (rhs < 0) ? 1 : -1;
return (lhs * rhs < 0) ? -((-lhs + x) / rhs) - 1 : lhs / rhs;
return ((lhs != 0) && ((lhs < 0) != (rhs < 0))) ? -((-lhs + x) / rhs) - 1
: lhs / rhs;
}
/// Returns MLIR's mod operation on constants. MLIR's mod operation yields the

4
mlir/unittests/Support/MathExtrasTest.cpp
View File

@ -17,6 +17,8 @@ TEST(MathExtrasTest, CeilDivTest) {
EXPECT_THAT(ceilDiv(14, -3), Eq(-4));
EXPECT_THAT(ceilDiv(-14, -3), Eq(5));
EXPECT_THAT(ceilDiv(-14, 3), Eq(-4));
EXPECT_THAT(ceilDiv(0, 3), Eq(0));
EXPECT_THAT(ceilDiv(0, -3), Eq(0));
}
TEST(MathExtrasTest, FloorDivTest) {
@ -24,4 +26,6 @@ TEST(MathExtrasTest, FloorDivTest) {
EXPECT_THAT(floorDiv(14, -3), Eq(-5));
EXPECT_THAT(floorDiv(-14, -3), Eq(4));
EXPECT_THAT(floorDiv(-14, 3), Eq(-5));
EXPECT_THAT(floorDiv(0, 3), Eq(0));
EXPECT_THAT(floorDiv(0, -3), Eq(0));
}