https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110413
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
Known to work| |11.4.0, 12.3.0
Last reconfirmed| |2023-06-27
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 13 eliminates the call in DOM3. The differences into that pass are quite
big with trunk having performed many more optimizations, in particular
we have elided the __builtin_unreachable () call already in DOM2 where
the first differences appears. We now manage to simplify the _24 != 0
branch.
@@ -79,22 +80,15 @@
_22 = _2 <= &d;
_23 = _2 != 0B;
_24 = _23 & _22;
- if (_24 != 0)
- goto <bb 5>; [100.00%]
- else
- goto <bb 4>; [0.00%]
+ goto <bb 4>; [100.00%]
<bb 3> [local count: 850510901]:
k = _2;
_3 = 1;
_1 = 1;
_15 = 1;
- goto <bb 5>; [100.00%]
-
- <bb 4> [count: 0]:
- __builtin_unreachable ();
- <bb 5> [local count: 955630225]:
+ <bb 4> [local count: 955630225]:
So we manage to optimize
<bb 3> [local count: 105119324]:
k = _2;
_22 = _2 <= &d;
_23 = _2 != 0B;
_24 = _23 & _22;
if (_24 != 0)
goto <bb 6>; [100.00%]
else
goto <bb 5>; [0.00%]
<bb 4> [local count: 850510901]:
k = _2;
_3 = _2 <= &d;
_1 = _2 != 0B;
_15 = _1 & _3;
if (_15 != 0)
goto <bb 6>; [100.00%]
else
goto <bb 5>; [0.00%]
<bb 5> [count: 0]:
__builtin_unreachable ();
<bb 6> [local count: 955630225]:
# h.4_25 = PHI <h.4_5(4), h.4_20(3)>
_4 = h.4_25 + -1;
h = _4;
h.4_5 = h;
if (h.4_5 != 0)
goto <bb 4>; [89.00%]
It seems we're now doing this based on the exported global range table
since we correctly first arrive at
Optimizing block #3
Optimizing statement k = _2;
LKUP STMT k = _2 with .MEM_11
LKUP STMT _2 = k with .MEM_11
LKUP STMT _2 = k with .MEM_21
2>>> STMT _2 = k with .MEM_21
Optimizing statement _22 = _2 <= &d;
LKUP STMT _22 = _2 le_expr &d
2>>> STMT _22 = _2 le_expr &d
LKUP STMT _2 ge_expr &d
Optimizing statement _23 = _2 != 0B;
LKUP STMT _23 = _2 ne_expr 0B
2>>> STMT _23 = _2 ne_expr 0B
Optimizing statement _24 = _23 & _22;
LKUP STMT _24 = _23 bit_and_expr _22
2>>> STMT _24 = _23 bit_and_expr _22
Optimizing statement if (_24 != 0)
Visiting conditional with predicate: if (_24 != 0)
With known ranges
_24: [irange] _Bool VARYING
Predicate evaluates to: DON'T KNOW
but then we register global ranges from the __builtin_unreachable () CFG:
# RANGE [irange] _Bool [1, 1]
_24 = _23 & _22;
and CFG cleanup scheduled by DOM does
static bool
cleanup_control_expr_graph (basic_block bb, gimple_stmt_iterator gsi)
{
...
case GIMPLE_COND:
{
gimple_match_op res_op;
if (gimple_simplify (stmt, &res_op, NULL, no_follow_ssa_edges,
no_follow_ssa_edges)
&& res_op.code == INTEGER_CST)
val = res_op.ops[0];
which now picks this up and elides the branch.
For some reason the "dead" stmts
<bb 2> [local count: 118111600]:
# PT = nonlocal null
_2 = j ();
i = _2;
k = _2;
# RANGE [irange] _Bool [1, 1]
_22 = _2 <= &d;
# RANGE [irange] _Bool [1, 1]
_23 = _2 != 0B;
# RANGE [irange] _Bool [1, 1]
_24 = _23 & _22;
allow us to optimize
k = _2;
# PT = nonlocal escaped null
k.5_6 = k;
_16 = k.5_6 == &g;
_17 = k.5_6 != 0B;
_18 = _17 | _16;
if (_18 != 0)
via
Optimizing statement _16 = k.5_6 == &g;
Replaced 'k.5_6' with variable '_2'
LKUP STMT _16 = _2 eq_expr &g
2>>> STMT _16 = _2 eq_expr &g
Optimizing statement _17 = k.5_6 != 0B;
Replaced 'k.5_6' with variable '_2'
LKUP STMT _17 = _2 ne_expr 0B
FIND: _23
Replaced redundant expr '_2 != 0B' with '_23'
==== ASGN _17 = _23
Optimizing statement _18 = _17 | _16;
Replaced '_17' with variable '_23'
Folded to: _18 = _16 | _23;
LKUP STMT _18 = _16 bit_ior_expr _23
2>>> STMT _18 = _16 bit_ior_expr _23
Optimizing statement if (_18 != 0)
Replaced '_18' with constant '1'
so it's kind of a missed optimization in the first DOM that elides the
stmts and the inability of ranger to capture the relations in the global
ranges.
