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link builtins in a way that lets unused functions get omitted from final library/binary #54

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andrewrk opened this Issue Jan 7, 2016 · 2 comments

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andrewrk commented Jan 7, 2016

when linking without libc, build memcpy.o and memset.o. we can cache these objects with a hash of (release/debug, conditional compilation values, target triple/data layout).

generate a compile unit without memcpy/memset exported. when linking the final output, use ar rcs foo.a foo.o memcpy.o memset.o. Then ld -o foo foo.a (or equivalent).

This accomplishes several things:

  • omit memcpy/memset when the functions are unused
  • avoid compiling memcpy/memset with every compiler invocation
  • allow linking zig-created .o files with libc .o files, so that a single project can have both c code and zig code and everything can be linked together. in this case zig generated code will depend on the libc memset/memcpy implementations.

@andrewrk andrewrk added the enhancement label Jan 7, 2016

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thejoshwolfe commented Jan 7, 2016

Why have separate memcpy.o and memset.o instead of prebuilding a mem.a and linking with ld -o foo foo.o mem.a? Doesn't that still provide the selective linking feature we want?

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andrewrk commented Jan 7, 2016

That should work too.

@andrewrk andrewrk added this to the debut milestone Jan 18, 2016

@andrewrk andrewrk removed this from the 0.1.0 milestone Mar 23, 2017

@andrewrk andrewrk added this to the 0.2.0 milestone May 7, 2017

@andrewrk andrewrk changed the title link against memcpy and memset properly link builtins in a way that lets unused functions get omitted from final library/binary May 21, 2017

@andrewrk andrewrk modified the milestones: 0.2.0, 0.3.0 Jan 3, 2018

@andrewrk andrewrk modified the milestones: 0.3.0, 0.4.0 Feb 28, 2018

@andrewrk andrewrk modified the milestones: 0.4.0, 0.5.0 Sep 28, 2018

andrewrk added a commit that referenced this issue Oct 8, 2018

andrewrk added a commit that referenced this issue Oct 9, 2018

@andrewrk andrewrk modified the milestones: 0.5.0, 0.4.0 Apr 8, 2019

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