On Mon, Mar 04, 2024 at 05:18:39PM +0100, Rainer Orth wrote: > > On 2/26/24 17:17, Greg McGary wrote: > >> The sign-bit-copies of a sign-extending load cannot be known until runtime > >> on > >> WORD_REGISTER_OPERATIONS targets, except in the case of a zero-extending > >> MEM > >> load. See the fix for PR112758. > >> 2024-02-22 Greg McGary <g...@rivosinc.com> > >> PR rtl-optimization/113010 > >> * combine.cc (simplify_comparison): Simplify a SUBREG on > >> WORD_REGISTER_OPERATIONS targets only if it is a zero-extending > >> MEM load. > >> * gcc.c-torture/execute/pr113010.c: New test. > > I think this is fine for the trunk. I'll do some final testing on it > > tomorrow. > > unfortunately, the patch broke Solaris/SPARC bootstrap > (sparc-sun-solaris2.11): > > /vol/gcc/src/hg/master/local/gcc/combine.cc: In function 'rtx_code > simplify_comparison(rtx_code, rtx_def**, rtx_def**)': > /vol/gcc/src/hg/master/local/gcc/combine.cc:12101:25: error: '*(unsigned > int*)((char*)&inner_mode + offsetof(scalar_int_mode, > scalar_int_mode::m_mode))' may be used uninitialized > [-Werror=maybe-uninitialized] > 12101 | scalar_int_mode mode, inner_mode, tmode; > | ^~~~~~~~~~
I don't see how it could ever work properly, inner_mode in that spot is just uninitialized. I think we shouldn't worry about paradoxical subregs of non-scalar_int_mode REGs/MEMs and for the scalar_int_mode ones should initialize inner_mode before we use it. Another option would be to use maybe_lt (GET_MODE_PRECISION (GET_MODE (SUBREG_REG (op0))), BITS_PER_WORD) and load_extend_op (GET_MODE (SUBREG_REG (op0))) == ZERO_EXTEND, or set machine_mode smode = GET_MODE (SUBREG_REG (op0)); and use it in those two spots. 2024-03-04 Jakub Jelinek <ja...@redhat.com> PR rtl-optimization/113010 * combine.cc (simplify_comparison): Guard the WORD_REGISTER_OPERATIONS check on scalar_int_mode of SUBREG_REG and initialize inner_mode. --- gcc/combine.cc.jj 2024-03-04 10:01:21.054937316 +0100 +++ gcc/combine.cc 2024-03-04 17:40:51.556052647 +0100 @@ -12554,6 +12554,8 @@ simplify_comparison (enum rtx_code code, if (paradoxical_subreg_p (op0)) { if (WORD_REGISTER_OPERATIONS + && is_a <scalar_int_mode> (GET_MODE (SUBREG_REG (op0)), + &inner_mode) && GET_MODE_PRECISION (inner_mode) < BITS_PER_WORD /* On WORD_REGISTER_OPERATIONS targets the bits beyond sub_mode aren't considered undefined, Jakub