| Message ID | 20240811054341.745674-1-joe@pf.is.s.u-tokyo.ac.jp (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | target/arm/tcg: Fix overflow in matrix-multiply accumulate | expand |
On 8/11/24 15:43, Joe Hattori wrote: > Arm's intrinsic matrix multiply accumulate instructions take two 8-bit > vector and add up a 32-bit vector. Current emulation causes overflow > when large 8-bit integers are used. This commit fixes the issue by > casting the 8-bit integers to 32-bit integers before multiplication. "Large 8-bit integers"? 0xff * 0xff = 0xfe01. This in no way overflows "int" on any supported host, which is the type we get via normal C arithmetic promotion rules. So what is this supposed to fix? r~ > > Fixes: 2323c5ffd4b5 ("target/arm: Implement integer matrix multiply accumulate") > Signed-off-by: Joe Hattori <joe@pf.is.s.u-tokyo.ac.jp> > --- > target/arm/tcg/vec_helper.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/target/arm/tcg/vec_helper.c b/target/arm/tcg/vec_helper.c > index 98604d170fd3..e9c33520232a 100644 > --- a/target/arm/tcg/vec_helper.c > +++ b/target/arm/tcg/vec_helper.c > @@ -2718,7 +2718,7 @@ static uint32_t do_smmla_b(uint32_t sum, void *vn, void *vm) > int8_t *n = vn, *m = vm; > > for (intptr_t k = 0; k < 8; ++k) { > - sum += n[H1(k)] * m[H1(k)]; > + sum += (uint32_t)n[H1(k)] * (uint32_t)m[H1(k)]; > } > return sum; > } > @@ -2728,7 +2728,7 @@ static uint32_t do_ummla_b(uint32_t sum, void *vn, void *vm) > uint8_t *n = vn, *m = vm; > > for (intptr_t k = 0; k < 8; ++k) { > - sum += n[H1(k)] * m[H1(k)]; > + sum += (uint32_t)n[H1(k)] * (uint32_t)m[H1(k)]; > } > return sum; > } > @@ -2739,7 +2739,7 @@ static uint32_t do_usmmla_b(uint32_t sum, void *vn, void *vm) > int8_t *m = vm; > > for (intptr_t k = 0; k < 8; ++k) { > - sum += n[H1(k)] * m[H1(k)]; > + sum += (uint32_t)n[H1(k)] * (uint32_t)m[H1(k)]; > } > return sum; > }
diff --git a/target/arm/tcg/vec_helper.c b/target/arm/tcg/vec_helper.c index 98604d170fd3..e9c33520232a 100644 --- a/target/arm/tcg/vec_helper.c +++ b/target/arm/tcg/vec_helper.c @@ -2718,7 +2718,7 @@ static uint32_t do_smmla_b(uint32_t sum, void *vn, void *vm) int8_t *n = vn, *m = vm; for (intptr_t k = 0; k < 8; ++k) { - sum += n[H1(k)] * m[H1(k)]; + sum += (uint32_t)n[H1(k)] * (uint32_t)m[H1(k)]; } return sum; } @@ -2728,7 +2728,7 @@ static uint32_t do_ummla_b(uint32_t sum, void *vn, void *vm) uint8_t *n = vn, *m = vm; for (intptr_t k = 0; k < 8; ++k) { - sum += n[H1(k)] * m[H1(k)]; + sum += (uint32_t)n[H1(k)] * (uint32_t)m[H1(k)]; } return sum; } @@ -2739,7 +2739,7 @@ static uint32_t do_usmmla_b(uint32_t sum, void *vn, void *vm) int8_t *m = vm; for (intptr_t k = 0; k < 8; ++k) { - sum += n[H1(k)] * m[H1(k)]; + sum += (uint32_t)n[H1(k)] * (uint32_t)m[H1(k)]; } return sum; }
Arm's intrinsic matrix multiply accumulate instructions take two 8-bit vector and add up a 32-bit vector. Current emulation causes overflow when large 8-bit integers are used. This commit fixes the issue by casting the 8-bit integers to 32-bit integers before multiplication. Fixes: 2323c5ffd4b5 ("target/arm: Implement integer matrix multiply accumulate") Signed-off-by: Joe Hattori <joe@pf.is.s.u-tokyo.ac.jp> --- target/arm/tcg/vec_helper.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)