On Wed, Mar 18, 2015 at 12:18 AM, Michael Meissner <meiss...@linux.vnet.ibm.com> wrote: > On Thu, Mar 12, 2015 at 11:37:14AM -0400, David Edelsohn wrote: >> Please check on the performance implications of removing the special >> constant support. I know that it is late, but I think that ripping it >> out is less risky than trying to fix this, if the performance impact >> is not bad. > > Now, I haven't drilled down to exactly what is causing the performance > differences, but I've done some Spec 2006 runs comparing subversion id 221194, > with the two patches. > > The first patch is a rewrite of the code that I originally put into the > compiler to move floating point constants under -ffast-math during the first > split pass. A minor tweak would need to be done to the original patch so that > it works with -mcmodel=small or -m32 options. > > The second patch completely eliminates keeping the non-0 constant around in > RTL, and pushes it to memory during the initial RTL generation, since it is > felt that the RTL optimizations no longer need the constant in RTL to convert > division by constant into multiplication by the reciprocal. > > The benchmarcks that show a difference are. Note, I do not count benchmarks > that differ by less than 2% to be significant. Percentages more than 100% > mean > the benchmark ran faster: > > Benchmark Patch-1 Patch-2 > ========= ======= ======= > 401.bzip2 102.59% 103.51% > 462.libquantum 100.28% 97.52% > 483.xalancbmk 97.72% 97.90% > 435.gromacs 104.48% 99.39% > 436.cactusADM 102.19% 102.90% > 470.lbm 100.39% 97.45% > Spec INT score 99.86% 99.86% > Spec FP score 100.50% 99.81% > > Patch #1 had 3 faster benchmarks and 1 slower benchmark. Patch #2 had 2 > faster > benchmarks, and 3 slower benchmarks.
Did you double-check if there are any differences in generated code? Esp. the SPEC INT benchmarks look odd - they don't contain any FP code. Richard. > I tend to feel patch #2 is cleaner, though it is slightly slower. However, I > can go with patch #1 if desired. > > Patch #2 bootstrapped fine, and had no regressions in the test suite. Did > you want me to install patch #1, patch #2, or do you want more information? > > [gcc] > 2015-03-17 Michael Meissner <meiss...@linux.vnet.ibm.com> > > PR target/65240 > * config/rs6000/predicates.md (easy_fp_constant): Remove special > -ffast-math handling that kept non-0 constants live in the RTL > until reload. Remove logic testing the number of instructions it > took to create a constant in a GPR that was never used, due to a > test for soft-float earlier. > (memory_fp_constant): Delete, no longer used. > > * config/rs6000/rs6000.md (mov<MODE>_hardfloat): Remove > alternatives for loading non-0 constants into GPRs for hard > floating point that is no longer needed due to changes in > easy_fp_constant. Add support for loading 0.0 into GPRs. > (mov<mode>_hardfloat32): Likewise. > (mov<mode>_hardfloat64): Likewise. > (mov<mode>_64bit_dm): Likewise. > (movtd_64bit_nodm): Likewise. > (pre-reload move FP constant define_split): Delete define_split, > since it is no longer used. > (extenddftf2_internal): Remove GHF constraints that are not valid > for extenddftf2. > > [gcc/testsuite] > 2015-03-17 Michael Meissner <meiss...@linux.vnet.ibm.com> > > PR target/65240 > * gcc/testsuite/g++.dg/pr65240.h: Add tests for PR 65240. > * gcc/testsuite/g++.dg/pr65240-1.C: Likewise. > * gcc/testsuite/g++.dg/pr65240-2.C: Likewise. > * gcc/testsuite/g++.dg/pr65240-3.C: Likewise. > * gcc/testsuite/g++.dg/pr65240-4.C: Likewise. > > -- > Michael Meissner, IBM > IBM, M/S 2506R, 550 King Street, Littleton, MA 01460-6245, USA > email: meiss...@linux.vnet.ibm.com, phone: +1 (978) 899-4797
