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
> >> 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*)_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
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 (GET_MODE (SUBREG_REG (op0)),
+_mode)
&& GET_MODE_PRECISION (inner_mode) < BITS_PER_WORD
/* On WORD_REGISTER_OPERATIONS targets the bits
beyond sub_mode aren't considered undefined,
Jakub
