tree 300d45c2f2721dce8ace5b889a1a0779556d4e73
parent 9269fa73ac6bc5eb4757923665b1d999f3587f16
author Cherry Zhang <cherryyz@google.com> 1560807922 -0400
committer Cherry Zhang <cherryyz@google.com> 1561146938 +0000

gollvm: wrap memmove, etc. in nosplit functions

When memmove (memcpy, memset) is called from a split-stack
function, the linker will change it to force a split by calling
__morestack_non_split, because the libc functions are external
and the linker has no knowledge about them. This may cause
many unnecessary stack splits.

However, the linker is happy if they are called from a nosplit
function. So we can work around it by wrapping memmove, etc. in
nosplit functions.

This CL adds nosplit wrappers functions, __go_memmove, etc.,
which (tail) calls memmove. Also add a LLVM backend pass, runs at
the end, changing calls to memmove, etc. to call the wrapper
functions.

Change-Id: Ic7e39281275ff7da14a8744ee56b4dc57c07321d
Reviewed-on: https://go-review.googlesource.com/c/gollvm/+/182817
Reviewed-by: Than McIntosh <thanm@google.com>