[PATCH] D79314: PR45733 : global weak symbol are excluded from the optimization .

[Umesh Kalappa via Phabricator via llvm-commits]

umesh.kalappa0 added a comment.

In D79314#2029834 <https://reviews.llvm.org/D79314#2029834>, @efriedma wrote:

> You still haven't explained why you think ConstantFolding is wrong, given the definition of weak_odr in LangRef.


@efriedma ,consider the below case ,

bft at bft-OptiPlex-5050:~$ cat weak.c
#pragma weak x

const int x = 5;

int foo ()

{ return x; }

bft at bft-OptiPlex-5050:~$ cat  main.c
int x =20;
int foo();

main()
{
 printf("weak linkage %d\n",foo());
}

bft at bft-OptiPlex-5050:~$ clang main.c weak.c
bft at bft-OptiPlex-5050:~$ ./a.out
weak linkage 20

bft at bft-OptiPlex-5050:~$ clang -O2 main.c weak.c
bft at bft-OptiPlex-5050:~$ ./a.out
weak linkage 5

with O2 <https://reviews.llvm.org/owners/package/2/> earlyCSE constant fold the variable "x" to constantl_5 (which is incorrect ) .so below fix was recommended to prevent the same.


Repository:
  rL LLVM

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  https://reviews.llvm.org/D79314/new/

https://reviews.llvm.org/D79314