[gcc r14-9304] combine: Fix recent WORD_REGISTER_OPERATIONS check [PR113010]

[gcc r14-9304] combine: Fix recent WORD_REGISTER_OPERATIONS check [PR113010]

[Jakub Jelinek]

https://gcc.gnu.org/g:901e7bdab70e2275723ac31dacbbce0b6f68f4f4

commit r14-9304-g901e7bdab70e2275723ac31dacbbce0b6f68f4f4
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Mon Mar 4 19:23:02 2024 +0100

    combine: Fix recent WORD_REGISTER_OPERATIONS check [PR113010]
    
    On Mon, Mar 04, 2024 at 05:18:39PM +0100, Rainer Orth wrote:
    > unfortunately, the patch broke Solaris/SPARC bootstrap
    > (sparc-sun-solaris2.11):
    >
    > .../gcc/combine.cc: In function 'rtx_code simplify_comparison(rtx_code, rtx_def**, rtx_def**)':
    > .../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  <jakub@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.

Diff:
---
 gcc/combine.cc | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/gcc/combine.cc b/gcc/combine.cc
index b09200d757e..a4479f8d836 100644
--- a/gcc/combine.cc
+++ b/gcc/combine.cc
@@ -12554,6 +12554,8 @@ simplify_comparison (enum rtx_code code, rtx *pop0, rtx *pop1)
 	  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,