https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123109
Bug ID: 123109
Summary: `a >> (bits-1) != 0` is not optimized to `a < 0` by
match
Product: gcc
Version: 16.0
Status: UNCONFIRMED
Keywords: internal-improvement
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: pinskia at gcc dot gnu.org
Blocks: 120206
Target Milestone: ---
This was kinda of noticed on accident via PR 123107.
But currently fold simplifies `(signed >> (sizeof(signed)*8-1)) != 0` into
`signed < 0` but match does not do it.
```
/* Fold (X >> C) != 0 into X < 0 if C is one less than the width
of X. Similarly fold (X >> C) == 0 into X >= 0. */
if (TREE_CODE (arg0) == RSHIFT_EXPR
&& integer_zerop (arg1)
&& TREE_CODE (TREE_OPERAND (arg0, 1)) == INTEGER_CST)
{
tree arg00 = TREE_OPERAND (arg0, 0);
tree arg01 = TREE_OPERAND (arg0, 1);
tree itype = TREE_TYPE (arg00);
if (wi::to_wide (arg01) == element_precision (itype) - 1)
{
if (TYPE_UNSIGNED (itype))
{
itype = signed_type_for (itype);
arg00 = fold_convert_loc (loc, itype, arg00);
}
return fold_build2_loc (loc, code == EQ_EXPR ? GE_EXPR : LT_EXPR,
type, arg00, build_zero_cst (itype));
}
}
```
Note for match, we need to expand_vec_cmp_expr_p (I think that is the correct
thing to check).
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120206
[Bug 120206] Removal of
forward_propagate_into_gimple_cond/forward_propagate_into_comparison
