https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101671
Bug ID: 101671
Summary: pr83510 fails because threader confuses -Warray-bounds
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: aldyh at gcc dot gnu.org
Target Milestone: ---
After my rewrite of the backwards threader with the ranger (commit
2e96b5f14e4025691b57d2301d71aa6092ed44bc), gcc.c-torture/compile/pr83510.c is
failing.
Here's a quote from my analysis in the test itself:
/* This test is XFAILed because thread1 threads a switch statement
such that the various cases have been split into different
independent blocks. One of these blocks exposes an arr[i_27]
which is later propagated by VRP to be arr[10]. This is an
invalid access, but the array bounds code doesn't know it is an
unreachable path.
However, it is not until dom2 that we "know" that the value of the
switch index is such that the path to arr[10] is unreachable. For
that matter, it is not until dom3 that we remove the unreachable
path.
See:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83510
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83312
It's not until here that ranger "knows" that the path is
unreachable:
thread1
vrp1 <-- array bounds checking
dce2
stdarg
cdce
cselim
copyprop
ifcombine
mergephi3 <-- too late
*/
