https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101179
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Blocks| |85316
--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #1)
> On IRC Richi said: "VRP has code to do that but maybe for some reason shifts
> are not handled"
Specifically simplify_using_ranges::simplify has
/* Convert:
LHS = CST BINOP VAR
Where VAR is two-valued and LHS is used in GIMPLE_COND only
To:
LHS = VAR == VAL1 ? (CST BINOP VAL1) : (CST BINOP VAL2)
Also handles:
LHS = VAR BINOP CST
Where VAR is two-valued and LHS is used in GIMPLE_COND only
To:
LHS = VAR == VAL1 ? (VAL1 BINOP CST) : (VAL2 BINOP CST) */
restrictions that stand in the way:
if (TREE_CODE_CLASS (rhs_code) == tcc_binary
...
&& single_imm_use (lhs, &use_p, &use_stmt)
&& gimple_code (use_stmt) == GIMPLE_COND)
VRP1 sees
<bb 2> [local count: 1073741824]:
_1 = y_7(D) % 100;
x_8 = _1 == 0;
_2 = (int) x_8;
_3 = _2 * 2;
_4 = 4 << _3;
_5 = y_7(D) % _4;
_6 = _5 == 0;
_9 = (int) _6;
return _9;
so it would consider _2 * 2 but its single use is in a shift, the
condition is after another op, the modulo, and there the condition
is in an assignment, not in a GIMPLE_COND.
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85316
[Bug 85316] [meta-bug] VRP range propagation missed cases
