CODEWITHSUNDEEP
clangllvm
ac-93
ac-93

Reputation: 11

clang -S -emit-llvm and then compile

I want to get exe with clang and llvm with two ways:

  1. clang -O2 1.c -o 1.exe
  2. clang -S -emit-llvm 1.c
    llc 1.ll -filetype=obj
    link 1.obj -defaultlib: ??? (MSVCRT or libcmt)

but exe files will different and first exe will faster, how to do it equal? Or how to see what clang use like defaultlib?

hard: windows 64.

Upvotes: 1

Views: 1116

Answers (1)

Carl Norum
Carl Norum

Reputation: 225132

You can add the -v flag on your first command line to see the linker invocation clang will use to build your program. As to the first executable being faster, that could be because you didn't pass any optimization flags in your second case.

I don't have a Windows machine handy, but here's some example output from my mac:

$ clang -v -O2 1.c -o 1.exe
Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn)
Target: x86_64-apple-darwin13.3.0
Thread model: posix
 "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang" -cc1 -triple x86_64-apple-macosx10.9.0 -emit-obj -disable-free -disable-llvm-verifier -main-file-name 1.c -mrelocation-model pic -pic-level 2 -mdisable-fp-elim -masm-verbose -munwind-tables -target-cpu core2 -target-linker-version 236.3 -v -resource-dir /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/clang/5.1 -O2 -fdebug-compilation-dir /Users/carl/Desktop/example -ferror-limit 19 -fmessage-length 80 -stack-protector 1 -mstackrealign -fblocks -fobjc-runtime=macosx-10.9.0 -fencode-extended-block-signature -fdiagnostics-show-option -fcolor-diagnostics -vectorize-loops -vectorize-slp -o /var/folders/mk/0mblc5810cjgs0nylrkjxqbm0000gq/T/1-7ac5d9.o -x c 1.c
clang -cc1 version 5.1 based upon LLVM 3.4svn default target x86_64-apple-darwin13.3.0
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/clang/5.1/include
 /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include
 /usr/include
 /System/Library/Frameworks (framework directory)
 /Library/Frameworks (framework directory)
End of search list.
 "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ld" -demangle -dynamic -arch x86_64 -macosx_version_min 10.9.0 -o 1.exe /var/folders/mk/0mblc5810cjgs0nylrkjxqbm0000gq/T/1-7ac5d9.o -lSystem /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/clang/5.1/lib/darwin/libclang_rt.osx.a

You can see the link line down at the bottom. Broken down for readability, its:

 ld 
  -demangle
  -dynamic
  -arch x86_64
  -macosx_version_min 10.9.0
  -o 1.exe
  $(OBJECT_FILE)
  -lSystem    
  libclang_rt.osx.a

Upvotes: 2

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