Thanks Pinski for comments. The outer convert here tries to align the in and out type of the SAT_MUL from the implementation. The type of Var[1|2|3] in below should be totally the same to align the standard name usmul<m>, like other sat_*, aka we don't have usmul<nm> now.
Var3 = SAT_MUL(Var1, Var2); Therefore the inner convert of @0 and @1 is required, as the form 13 needs the widen type for mul. Do we need to adjust the sematics of SAT_MUL? Or keep it as is for now. Pan -----Original Message----- From: Andrea Pinski <[email protected]> Sent: Thursday, June 18, 2026 11:39 AM To: Li, Pan2 <[email protected]> Cc: [email protected]; [email protected]; [email protected]; [email protected]; [email protected]; Chen, Ken <[email protected]>; Liu, Hongtao <[email protected]>; [email protected] Subject: Re: [PATCH v2 1/3] Match: Support unsigned scalar SAT_MUL form 13 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. 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 >
