On Thu, Feb 13, 2020 at 2:46 PM Alexander Monakov <amona...@ispras.ru> wrote: > > Ping^3.
OK. > On Sun, 5 Jan 2020, Alexander Monakov wrote: > > > Hi, > > > > I noticed there's a costly signed 64-bit division in rtx_cost on x86 as > > well as > > any other target where UNITS_PER_WORD is implemented like TARGET_64BIT ? 8 > > : 4. > > It's also evident that rtx_cost does redundant work for a SET rtx argument. > > > > Obviously the variable named 'factor' rarely exceeds 1, so in the majority > > of > > cases it can be computed with a well-predictable branch rather than a > > division. > > > > This patch makes rtx_cost do the division only in case mode is wider than > > UNITS_PER_WORD, and also moves a test for a SET up front to avoid > > redundancy. > > No functional change. > > > > Bootstrapped on x86_64, ok for trunk? > > > > To illustrate the improvement this buys, for tramp3d -O2 compilation, I got > > > > before: > > 73887675319 instructions:u > > > > 72438432200 cycles:u > > 924298569 idq.ms_uops:u > > 102603799255 uops_dispatched.thread:u > > > > after: > > 73888371724 instructions:u > > > > 72386986612 cycles:u > > 802744775 idq.ms_uops:u > > 102096987220 uops_dispatched.thread:u > > > > (this is on Sandybridge, idq.ms_uops are uops going via the microcode > > sequencer, > > so the unneeded division is responsible for a good fraction of them) > > > > * rtlanal.c (rtx_cost): Handle a SET up front. Avoid division if the > > mode is not wider than UNITS_PER_WORD. > > > > diff --git a/gcc/rtlanal.c b/gcc/rtlanal.c > > index 9a7afccefb8..c7ab86e228b 100644 > > --- a/gcc/rtlanal.c > > +++ b/gcc/rtlanal.c > > @@ -4207,18 +4207,23 @@ rtx_cost (rtx x, machine_mode mode, enum rtx_code > > outer_code, > > const char *fmt; > > int total; > > int factor; > > + unsigned mode_size; > > > > if (x == 0) > > return 0; > > > > - if (GET_MODE (x) != VOIDmode) > > + if (GET_CODE (x) == SET) > > + /* A SET doesn't have a mode, so let's look at the SET_DEST to get > > + the mode for the factor. */ > > + mode = GET_MODE (SET_DEST (x)); > > + else if (GET_MODE (x) != VOIDmode) > > mode = GET_MODE (x); > > > > + mode_size = estimated_poly_value (GET_MODE_SIZE (mode)); > > + > > /* A size N times larger than UNITS_PER_WORD likely needs N times as > > many insns, taking N times as long. */ > > - factor = estimated_poly_value (GET_MODE_SIZE (mode)) / UNITS_PER_WORD; > > - if (factor == 0) > > - factor = 1; > > + factor = mode_size > UNITS_PER_WORD ? mode_size / UNITS_PER_WORD : 1; > > > > /* Compute the default costs of certain things. > > Note that targetm.rtx_costs can override the defaults. */ > > @@ -4243,14 +4248,6 @@ rtx_cost (rtx x, machine_mode mode, enum rtx_code > > outer_code, > > /* Used in combine.c as a marker. */ > > total = 0; > > break; > > - case SET: > > - /* A SET doesn't have a mode, so let's look at the SET_DEST to get > > - the mode for the factor. */ > > - mode = GET_MODE (SET_DEST (x)); > > - factor = estimated_poly_value (GET_MODE_SIZE (mode)) / > > UNITS_PER_WORD; > > - if (factor == 0) > > - factor = 1; > > - /* FALLTHRU */ > > default: > > total = factor * COSTS_N_INSNS (1); > > } > >
