[PATCH] D49362: [ThinLTO] Internalize read only globals

[Evgeny Leviant via llvm-commits]

Thanks for making reproducer, Steven!


It turned out cache key is computed differently by newer API (LTO.cpp) and legacy API (ThinLTOCodeGenerator).

I was always wondering what piece of software uses legacy API and finally found this out - it is Mac OS X linker ld64.


On Linux lld and gold plugin use newer API, so the bug can't be reproduced.

________________________________
От: stevenwu at apple.com <stevenwu at apple.com> от имени Steven Wu <stevenwu at apple.com>
Отправлено: 15 ноября 2018 г. 3:34
Кому: Teresa Johnson
Копия: Evgeny Leviant; Mehdi AMINI; reviews+D49362+public+6f0316d7b1456727 at reviews.llvm.org; Xin Tong; Alex L; Daniel Grumberg; JF Bastien; Anton Korobeynikov; Bob Haarman; Easwaran Raman; Duncan Exon Smith; llvm-commits; George Rimar; Igor Kudrin; jun.l at samsung.com
Тема: Re: [PATCH] D49362: [ThinLTO] Internalize read only globals

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On Nov 14, 2018, at 4:28 PM, Teresa Johnson <tejohnson at google.com<mailto:tejohnson at google.com>> wrote:



On Wed, Nov 14, 2018 at 1:47 PM Steven Wu <stevenwu at apple.com<mailto:stevenwu at apple.com>> wrote:
Here is a small reduced test case using the same main.c and foo.c from the review:
cat main.c
int foo();
int main() {
  return foo();
}

cat foo.c
#include <stdlib.h>
static int gFoo = 1;
int foo() {
  return gFoo;
}
void bar() {
  gFoo = rand();
}

cat test1.c
int foo();
int test() {
  return foo();
}

cat test2.c
int foo();
int bar();
int test() {
  return foo() + bar();
}

To reproduce:
$ clang -O3 -flto=thin -c main.c test1.c test2.c foo.c
$ clang -O3 -flto=thin -Wl,-cache_path_lto,lto.cache main.o test2.o foo.o
$ clang -O3 -flto=thin -Wl,-cache_path_lto,lto.cache main.o test1.o foo.o
Undefined symbols for architecture x86_64:
  "_gFoo.llvm.17695746433417383459", referenced from:
      _main in lto.o

I can't reproduce this, although I am using gold (with  -Wl,-plugin-opt,cache-dir=lto.cache) since I don't have ld64. I notice that test() is dead, so with gold at least it is removed completely.

Do you have any temp files you can share (i.e. IR before and after importing)?

Attach all the intermediate file. I haven't had time to look in detail yet.

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