https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120283
Bug ID: 120283
Summary: `Transform comparisons of the form X +- C1 CMP C2 to X
CMP C2 -+ C1` gimple depends on single use
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Keywords: internal-improvement
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: pinskia at gcc dot gnu.org
Reporter: pinskia at gcc dot gnu.org
Blocks: 120206
Target Milestone: ---
Forwprop for comparisons proping uses generic rather than gimple so it will
cause to ignore single use in many cases.
So in this case of this pattern:
```
/* Transform comparisons of the form X +- C1 CMP C2 to X CMP C2 -+ C1. */
(for cmp (eq ne)
(for op (plus minus)
rop (minus plus)
(simplify
(cmp (op@3 @0 INTEGER_CST@1) INTEGER_CST@2)
(if (!TREE_OVERFLOW (@1) && !TREE_OVERFLOW (@2)
&& !TYPE_OVERFLOW_SANITIZED (TREE_TYPE (@0))
&& !TYPE_OVERFLOW_TRAPS (TREE_TYPE (@0))
&& !TYPE_SATURATING (TREE_TYPE (@0)))
(with { tree res = int_const_binop (rop, @2, @1); }
(if (TREE_OVERFLOW (res)
&& TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (@0)))
{ constant_boolean_node (cmp == NE_EXPR, type); }
(if (single_use (@3))
(cmp @0 { TREE_OVERFLOW (res)
? drop_tree_overflow (res) : res; }))))))))
```
forwprop ignores the single use there as it does combining into generic and
then uses generic to do the simplification.
I am thinking single use is not important here after all and has been ignored
anyways.
The pattern with single use was added with r7-502-ga8b85ce9e2bffc.
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
