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 <j...@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;
}
