https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110748
--- Comment #14 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Vineet Gupta <vine...@gcc.gnu.org>: https://gcc.gnu.org/g:ecfa870ff29d979bd2c3d411643b551f2b6915b0 commit r14-2731-gecfa870ff29d979bd2c3d411643b551f2b6915b0 Author: Vineet Gupta <vine...@rivosinc.com> Date: Thu Jul 20 11:15:37 2023 -0700 RISC-V: optim const DF +0.0 store to mem [PR/110748] Fixes: ef85d150b5963 ("RISC-V: Enable TARGET_SUPPORTS_WIDE_INT") DF +0.0 is bitwise all zeros so int x0 store to mem can be used to optimize it. void zd(double *) { *d = 0.0; } currently: | fmv.d.x fa5,zero | fsd fa5,0(a0) | ret With patch | sd zero,0(a0) | ret The fix updates predicate const_0_operand() so reg_or_0_operand () now includes const_double, enabling movdf expander -> riscv_legitimize_move () to generate below vs. an intermediate set (reg:DF) const_double:DF | (insn 6 3 0 2 (set (mem:DF (reg/v/f:DI 134 [ d ]) | (const_double:DF 0.0 [0x0.0p+0])) This change also enables such insns to be recog() by later passes. The md pattern "*movdf_hardfloat_rv64" despite already supporting the needed constraints {"m","G"} mem/const 0.0 was failing to match because the additional condition check reg_or_0_operand() was failing due to missing const_double. This failure to recog() was triggering an ICE when testing the in-flight f-m-o patches and is how all of this started, but then was deemed to be an independent optimization of it's own [1]. [1] https://gcc.gnu.org/pipermail/gcc-patches/2023-July/624857.html Its worthwhile to note all the set peices were already there and working up until my own commit mentioned at top regressed the whole thing. Ran thru full multilib testsuite and no surprises. There was 1 false failure due to random string "lw" appearing in lto build assembler output, which is also fixed here. gcc/ChangeLog: PR target/110748 * config/riscv/predicates.md (const_0_operand): Add back const_double. gcc/testsuite/ChangeLog: * gcc.target/riscv/pr110748-1.c: New Test. * gcc.target/riscv/xtheadfmv-fmv.c: Add '\t' around test patterns to avoid random string matches. Signed-off-by: Vineet Gupta <vine...@rivosinc.com>
