https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127440
Bug ID: 127440
Summary: cond_store_replacement_limited should support diamond
shapped bb
Product: gcc
Version: 17.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: enhancement
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: pinskia at gcc dot gnu.org
Target Milestone: ---
Created attachment 65614
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=65614&action=edit
testcase
Sometimes (and due to other factoring), we are left with diamond shapped cfg
and cond_store_replacement_limited will not do anything with it.
This is wrong as we should be able to handle it as long as the store is before
the condition.
A reduced example is attached; though this can show up with some more complex
factoring in really; an example is gcc.dg/tree-ssa/ssa-dom-cse-3.c if we factor
out the load and we are left with:
```
<bb 2> :
a = 0;
if (b_5(D) != 0)
goto <bb 3>; [INV]
else
goto <bb 4>; [INV]
<bb 3> :
a = 1;
// predicted unlikely by early return (on trees) predictor.
goto <bb 5>; [INV]
<bb 4>:
<bb 5> :
_1 = a;
return _1;
```
Which then we can do a cs-elim too on the a but currently do because of the
extra bb.
