https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99383
Bug ID: 99383
Summary: No tree-switch-conversion under PIC
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: jengelh at inai dot de
Target Milestone: ---
== Input source ==
enum {
itm01, itm02, itm03, itm04, itm05, itm06, itm07, itm08, itm09, itm0A, itm0B,
itm0C, itm0D, itm0E, itm0F, itm10,
};
#define E(s) case s: return #s;
const char *r2i(unsigned int i) {
switch (i) {
E(itm01) E(itm02) E(itm03) E(itm04) E(itm05) E(itm06) E(itm07)
E(itm08) E(itm09) E(itm10)
}
return "";
}
== Expected output ==
» g++-11 -v x.cpp -c -O2
» objdump -d x.o
0000000000000000 <_Z3r2ij>:
0: b8 00 00 00 00 mov $0x0,%eax
5: 83 ff 0f cmp $0xf,%edi
8: 77 0a ja 14 <_Z3r2ij+0x14>
a: 89 ff mov %edi,%edi
c: 48 8b 04 fd 00 00 00 mov 0x0(,%rdi,8),%rax
13: 00
14: c3 ret
0x0(,%rdi,8) points to a CSWTCH symbol generated by gcc's
tree-switch-conversion.c.
== Observed behavior with extra flag ==
When enabling pic/PIC, tree-switch-conversion optimization is completely missed
and a lot of lea/ret instruction pairs are generated.
» g++-11 -v x.cpp -c -O2 -fpic
Target: x86_64-suse-linux
gcc version 11.0.0 20210208 (experimental) [revision
efcd941e86b507d77e90a1b13f621e036eacdb45] (SUSE Linux)
...
» objdump -d x.o
…
20: 48 8d 05 00 00 00 00 lea 0x0(%rip),%rax # 27
<_Z3r2ij+0x27>
27: c3 ret
28: 0f 1f 84 00 00 00 00 nopl 0x0(%rax,%rax,1)
2f: 00
30: 48 8d 05 00 00 00 00 lea 0x0(%rip),%rax # 37
<_Z3r2ij+0x37>
37: c3 ret
…
