[Bug tree-optimization/111293] [14 Regression] Missed Dead Code Elimination since r14-3414-g0cfc9c953d0
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111293
--- Comment #4 from Mikael Morin ---
For what's worth adding -fno-tree-vrp "fixes" this and enables removal of the
call to 'foo' with trunk.
Here is a minimal revert of the regressing revision, but it may just make the
problem latent.
diff --git a/gcc/gimple-range-phi.cc b/gcc/gimple-range-phi.cc
index 01900a35b32..9fa9fe83ce0 100644
--- a/gcc/gimple-range-phi.cc
+++ b/gcc/gimple-range-phi.cc
@@ -386,14 +386,6 @@ phi_analyzer::process_phi (gphi *phi)
m_work.safe_push (arg);
continue;
}
- // More than 2 outside names is too complicated.
- if (m_num_extern >= 2)
- {
- cycle_p = false;
- break;
- }
- m_external[m_num_extern] = arg;
- m_ext_edge[m_num_extern++] = gimple_phi_arg_edge (phi_stmt, x);
}
else if (code == INTEGER_CST)
{
@@ -402,12 +394,15 @@ phi_analyzer::process_phi (gphi *phi)
wi::to_wide (arg));
init_range.union_ (val);
}
- else
+ // More than 2 outside names/CONST is too complicated.
+ if (m_num_extern >= 2)
{
- // Everything else terminates the cycle.
cycle_p = false;
break;
}
+
+ m_external[m_num_extern] = arg;
+ m_ext_edge[m_num_extern++] = gimple_phi_arg_edge (phi_stmt, x);
}
}
[Bug tree-optimization/111293] [14 Regression] Missed Dead Code Elimination since r14-3414-g0cfc9c953d0
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111293 Mikael Morin changed: What|Removed |Added CC||mikael at gcc dot gnu.org --- Comment #3 from Mikael Morin --- pre replaces usages of the 'e' global with a set of 'pretmp' and 'prephitmp' ssa registers. With gcc-13, the value of 'e' is reloaded directly after the call to 'foo', and that value is joined with a phi in the next bb: [local count: 7761689018]: foo (); pretmp_25 = e; goto ; [100.00%] ... [local count: 8963573811]: # j_28 = PHI <1(10), j_30(24), 1(22), j_30(25), 1(26), j_30(20)> # i_29 = PHI # prephitmp_38 = PHI d.7_22 = d; _23 = d.7_22 + 1; d = _23; if (_23 != 0) goto ; [94.50%] else goto ; [5.50%] With gcc-14, the value of 'e' is reloaded later in the next bb, causing a dependency on 'e', even on paths not calling 'foo': [local count: 7761689018]: foo (); goto ; [100.00%] ... [local count: 8963573796]: # i_28 = PHI d.7_22 = d; _23 = d.7_22 + 1; d = _23; pretmp_10 = e; if (_23 != 0) goto ; [94.50%] else goto ; [5.50%] Later on this prevents copyprop from simplifying the 'pretmp' and 'prephitmp' values to 3 and remove the branch calling 'foo'.
[Bug tree-optimization/111293] [14 Regression] Missed Dead Code Elimination since r14-3414-g0cfc9c953d0
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111293 Jeffrey A. Law changed: What|Removed |Added Priority|P3 |P2 CC||law at gcc dot gnu.org
[Bug tree-optimization/111293] [14 Regression] Missed Dead Code Elimination since r14-3414-g0cfc9c953d0
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111293 --- Comment #2 from Andrew Macleod --- It seems like we set 'e' to 3 immediately at the start: [local count: 1073741824]: e = 3; goto ; [100.00%] and it is never changed again. However, when we load from 'e' later in the IL [local count: 9485263241]: e.1_6 = e; we simply get varying. Is some pass suppose to propagate this? This reminds me of a few other regression PRs where we no longer propagate known values from loads from memory into ssa-names. If we knew that e.1_6 was '3', then the call to foo would be folded away as never executable.
[Bug tree-optimization/111293] [14 Regression] Missed Dead Code Elimination since r14-3414-g0cfc9c953d0
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111293 Andrew Pinski changed: What|Removed |Added Ever confirmed|0 |1 Last reconfirmed||2023-09-05 Status|UNCONFIRMED |NEW
[Bug tree-optimization/111293] [14 Regression] Missed Dead Code Elimination since r14-3414-g0cfc9c953d0
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111293 --- Comment #1 from Andrew Pinski --- The difference is the trunk can figure out the range for j_8: PHI GROUP query for j_8 found : [irange] int [1, 1][8, 8] and adjusted original range from :[irange] int [1, 1][8, 8] to :[irange] int [1, 1][8, 8] Global Exported: j_8 = [irange] int [1, 1][8, 8] MASK 0x9 VALUE 0x8 But 13 can't: Global Exported: j_8 = [irange] int [-INF, +INF] NONZERO 0x9 I have not looked into how 13 can remove the call to foo though.
[Bug tree-optimization/111293] [14 Regression] Missed Dead Code Elimination since r14-3414-g0cfc9c953d0
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111293 Andrew Pinski changed: What|Removed |Added Keywords||missed-optimization Target Milestone|--- |14.0
