On Wed, Jun 17, 2026 at 8:38 PM Andrea Pinski
<[email protected]> wrote:
>
> On Wed, Jun 17, 2026 at 5:47 PM <[email protected]> wrote:
> >
> > From: Pan Li <[email protected]>
> >
> > This patch would like to try to match the the unsigned
> > SAT_MUL form 13, aka below
> >
> > #define DEF_SAT_U_MUL_FMT_13(NT, WT) \
> > NT __attribute__((noinline)) \
> > sat_u_mul_##NT##_from_##WT##_fmt_13 (NT a, NT b) \
> > { \
> > WT x = (WT)a * (WT)b; \
> > if ((x >> sizeof(a) * 8) != 0) \
> > return (NT)-1; \
> > else \
> > return (NT)x; \
> > }
> >
> > while WT is uint128_t, uint64_t, uint32_t and uint16_t, and
> > NT is uint64_t, uint32_t, uint16_t or uint8_t.
> >
> > gcc/ChangeLog:
> >
> > * match-sat-alu.pd: Add pattern for unsigned scalar
> > SAT_MUL form 13.
> >
> > Signed-off-by: Pan Li <[email protected]>
> > ---
> > gcc/match-sat-alu.pd | 25 +++++++++++++++++++++++++
> > 1 file changed, 25 insertions(+)
> >
> > diff --git a/gcc/match-sat-alu.pd b/gcc/match-sat-alu.pd
> > index 6145a0c9948..c47d73f958d 100644
> > --- a/gcc/match-sat-alu.pd
> > +++ b/gcc/match-sat-alu.pd
> > @@ -524,6 +524,31 @@ along with GCC; see the file COPYING3. If not see
> > bool c2_is_type_precision_p = c2 == prec;
> > }
> > (if (widen_prec > prec && c2_is_type_precision_p && c4_is_max_p)))))
> > + (match (unsigned_integer_sat_mul @0 @1)
> > + /* SAT_U_MUL (X, Y) = {
> > + WT x = (WT)a * (WT)b;
> > + if ((x >> sizeof(a) * 8) != 0)
> > + return (T)-1;
> > + else
> > + return (T)x;
> > + }
> > + while WT is uint128_t, T is uint8_t, uint16_t, uint32_t or uint64_t.
> > */
> > + (convert (cond^ (ne (rshift (mult:c@3 (convert @0) (convert @1))
> > + INTEGER_CST@2)
> > + integer_zerop)
> > + INTEGER_CST@4 @3))
> > + (if (types_match (type, @0, @1) && tree_fits_uhwi_p (@2))
> > + (with
> > + {
> > + unsigned prec = TYPE_PRECISION (type);
> > + unsigned widen_prec = TYPE_PRECISION (TREE_TYPE (@3));
> > + wide_int c4 = wi::to_wide (@4);
> > + wide_int max = wi::mask (prec, false, widen_prec);
> > + bool c4_is_max_p = wi::eq_p (c4, max);
> > + unsigned c2 = tree_to_uhwi (@2);
> > + bool c2_is_type_precision_p = c2 == prec;
> > + }
> > + (if (widen_prec > prec && c2_is_type_precision_p && c4_is_max_p)))))
>
> Hmm, is there a way to match without the outer convert here? Because
> even without that convert it will be unsigned sat mult with a type
> precision of @2.
If we can't, then this patch seems reasonable.
> Also I think the inner converts can be removed if we fit into unsigned
> precision of that same type.
> There is a ranger helper function for ranges to answer that question.
>
> I am not saying we need to remove those currently just that it might be
> useful.
>
> An example there would be:
> ```
> uint32_t f (uint32_t a, uint32_t b) {
> uint32_t x = ((uint32_t)(uint16_t)a) * (uint32_t)(uint16_t)b;
> if ((x >> sizeof(uint16_t) * 8) != 0)
> return (uint16_t)-1;
> else
> return (uint16_t)x;
> }
> uint32_t f1 (uint16_t a, uint16_t b) {
> uint32_t x = ((uint32_t)(uint16_t)a) * (uint32_t)(uint16_t)b;
> if ((x >> sizeof(uint16_t) * 8) != 0)
> return (uint16_t)-1;
> else
> return (uint16_t)x;
> }
> ```
>
> I noticed that LLVM is not able to handle f but does handle f1.
>
>
> > (match (unsigned_integer_sat_mul @0 @1)
> > /* SAT_U_MUL (X, Y) = {
> > WT x = (WT)a * (WT)b;
> > --
> > 2.43.0
> >
