tree-ssa-math-opts: Fix is_widening_mult_rhs_p - unbreak bootstrap [PR113705]

tree-ssa-math-opts: Fix is_widening_mult_rhs_p - unbreak bootstrap [PR113705]

On Tue, Jan 30, 2024 at 07:33:10AM -0000, Roger Sayle wrote:
+             wide_int bits = wide_int::from (tree_nonzero_bits (rhs),
+                                             prec,
+                                             TYPE_SIGN (TREE_TYPE (rhs)));
...
> +               if (gimple_assign_rhs_code (stmt) == BIT_AND_EXPR
> +                   && TREE_CODE (gimple_assign_rhs2 (stmt)) == INTEGER_CST
> +                   && wi::to_wide (gimple_assign_rhs2 (stmt))
> +                      == wi::mask (hprec, false, prec))

This change broke bootstrap on aarch64-linux.
The problem can be seen even on the reduced testcase.

The IL on the unreduced testcase before widening_mul has:
  # val_583 = PHI <val_26(13), val_164(40)>
...
  pretmp_266 = MEM[(const struct wide_int_storage *)&D.160657].len;
  _264 = pretmp_266 & 65535;
...
  _176 = (sizetype) val_583;
  _439 = (sizetype) _264;
  _284 = _439 * 8;
  _115 = _176 + _284;
where 583/266/264 have unsigned int type and 176/439/284/115 have sizetype.
widening_mul first turns that into:
  # val_583 = PHI <val_26(13), val_164(40)>
...
  pretmp_266 = MEM[(const struct wide_int_storage *)&D.160657].len;
  _264 = pretmp_266 & 65535;
...
  _176 = (sizetype) val_583;
  _439 = (sizetype) _264;
  _284 = _264 w* 8;
  _115 = _176 + _284;
and then is_widening_mult_rhs_p is called, with type sizetype (64-bit),
rhs _264, hprec 32 and prec 64.  Now tree_nonzero_bits (rhs) is
65535, so bits is 64-bit wide_int 65535, stmt is BIT_AND_EXPR,
but we ICE on the
wi::to_wide (gimple_assign_rhs2 (stmt)) == wi::mask (hprec, false, prec)
comparison because wi::to_wide on gimple_assign_rhs2 (stmt) - unsigned int
65535 gives 32-bit wide_int 65535, while wi::mask (hprec, false, prec)
gives 64-bit wide_int 0xffffffff and comparison between different precision
wide_ints is forbidden.

The following patch fixes it the same way how bits is computed earlier,
by calling wide_int::from on the wi::to_wide (gimple_assign_rhs2 (stmt)),
so we compare 64-bit 65535 with 64-bit 0xffffffff.

2024-02-02  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/113705
	* tree-ssa-math-opts.cc (is_widening_mult_rhs_p): Use wide_int_from
	around wi::to_wide in order to compare value in prec precision.

	* g++.dg/opt/pr113705.C: New test.