For a definition (of most linkage types), dso_local is set for ELF -fno-pic/-fpie
and COFF, but not for Mach-O. This nuance causes unneeded binary format differences.
This patch replaces (function) `define ` with `define{{.*}} `,
(variable/constant/alias) `= ` with `={{.*}} `, or inserts appropriate `{{.*}} `
if there is an explicit linkage.
* Clang will set dso_local for Mach-O, which is currently implied by TargetMachine.cpp. This will make COFF/Mach-O and executable ELF similar.
* Eventually I hope we can make dso_local the textual LLVM IR default (write explicit "dso_preemptable" when applicable) and -fpic ELF will be similar to everything else. This patch helps move toward that goal.
And another step towards transforms not introducing inttoptr and/or
ptrtoint casts that weren't there already.
As we've been establishing (see D88788/D88789), if there is a int<->ptr cast,
it basically must stay as-is, we can't do much with it.
I've looked, and the most source of new such casts being introduces,
as far as i can tell, is this transform, which, ironically,
tries to reduce count of casts..
On vanilla llvm test-suite + RawSpeed, @ `-O3`, this results in
-33.58% less `IntToPtr`s (19014 -> 12629)
and +76.20% more `PtrToInt`s (18589 -> 32753),
which is an increase of +20.69% in total.
However just on RawSpeed, where i know there are basically
none `IntToPtr` in the original source code,
this results in -99.27% less `IntToPtr`s (2724 -> 20)
and +82.92% more `PtrToInt`s (4513 -> 8255).
which is again an increase of 14.34% in total.
To me this does seem like the step in the right direction,
we end up with strictly less `IntToPtr`, but strictly more `PtrToInt`,
which seems like a reasonable trade-off.
See https://reviews.llvm.org/D88860 / https://reviews.llvm.org/D88995
for some more discussion on the subject.
(Eventually, `CastInst::isNoopCast()`/`CastInst::isEliminableCastPair`
should be taught about this, yes)
Reviewed By: nlopes, nikic
Differential Revision: https://reviews.llvm.org/D88979
Fangrui Song