On 29 June 2018 at 09:29, Peter Maydell <peter.mayd...@linaro.org> wrote: > On 29 June 2018 at 01:15, Richard Henderson > <richard.hender...@linaro.org> wrote: >> We already check for the same condition within the normal integer >> sdiv and sdiv64 helpers. Use a slightly different formation that >> does not require deducing the expression type. >> >> Fixes: f97cfd596ed >> Signed-off-by: Richard Henderson <richard.hender...@linaro.org> >> --- >> target/arm/sve_helper.c | 16 +++++++++++----- >> 1 file changed, 11 insertions(+), 5 deletions(-) >> >> diff --git a/target/arm/sve_helper.c b/target/arm/sve_helper.c >> index 790cbacd14..7d7fc90566 100644 >> --- a/target/arm/sve_helper.c >> +++ b/target/arm/sve_helper.c >> @@ -369,7 +369,13 @@ void HELPER(NAME)(void *vd, void *vn, void *vm, void >> *vg, uint32_t desc) \ >> #define DO_MIN(N, M) ((N) >= (M) ? (M) : (N)) >> #define DO_ABD(N, M) ((N) >= (M) ? (N) - (M) : (M) - (N)) >> #define DO_MUL(N, M) (N * M) >> -#define DO_DIV(N, M) (M ? N / M : 0) >> + >> +/* The zero divisor case is architectural; the -1 divisor case works >> + * around the x86 INT_MIN / -1 overflow exception without having to >> + * deduce the minimum integer for the type of the expression. >> + */ > > It works around INT_MIN / -1 being C undefined behaviour: the > need to special-case this is not x86-specific... The required > answer for Arm is just as architectural as the required answer > for division-by-zero (which is also C UB).
Suggested revised comment text: /* We must avoid the C undefined behaviour cases: division by * zero and signed division of INT_MIN by -1. Both of these * have architecturally defined required results for Arm. * We special case all signed divisions by -1 to avoid having * to deduce the minimum integer for the type involved. */ ? thanks -- PMM
