Applied to master. Thanks! Note that the multiply-by-200 (in the testcase) originates from Dhrystone.
Philipp. On Sun, 13 Nov 2022 at 02:23, Jeff Law <jeffreya...@gmail.com> wrote: > > > On 11/10/22 14:34, Philipp Tomsich wrote: > > The strength-reduction implementation in expmed.cc will assess the > > profitability of using shift-and-add using a RTL expression that wraps > > a MULT (with a power-of-2) in a PLUS. Unless the RISC-V rtx_costs > > function recognizes this as expressing a sh[123]add instruction, we > > will return an inflated cost---thus defeating the optimization. > > > > This change adds the necessary idiom recognition to provide an > > accurate cost for this for of expressing sh[123]add. > > > > Instead on expanding to > > li a5,200 > > mulw a0,a5,a0 > > with this change, the expression 'a * 200' is sythesized as: > > sh2add a0,a0,a0 // *5 = a + 4 * a > > sh2add a0,a0,a0 // *5 = a + 4 * a > > slli a0,a0,3 // *8 > > > > gcc/ChangeLog: > > > > * config/riscv/riscv.c (riscv_rtx_costs): Recognize shNadd, > > if expressed as a plus and multiplication with a power-of-2. > > Split costing for MINUS from PLUS. > > > > gcc/testsuite/ChangeLog: > > > > * gcc.target/riscv/zba-shNadd-07.c: New test. > > OK. Note that getting this right can impact one of the spec2017 integer > benchmarks notably. I don't recall which one, but it has a div and a > mod by the same constant which is fairly reasonably implement with > shifts and adds. You won't see it in instruction count data, but would > see it if you had cycle count data or instrumented for div/mod instructions. > > > Jeff > >
