llvm flang使用

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flang -help

Flang编译器支持接受所有clang 4.0编译器选项，并支持许多以及以下特定于flang的编译器选项：

• -noFlangLibs Do not link against Flang libraries
• -mp Enable OpenMP and link with with OpenMP library libomp
• -nomp Do not link with OpenMP library libomp
• -Mbackslash Treat backslash character like a C-style escape character
• -Mno-backslash Treat backslash like any other character
• -Mbyteswapio Swap byte-order for unformatted input/output
• -Mfixed Assume fixed-format source
• -Mextend Allow source lines up to 132 characters
• -Mfreeform Assume free-format source
• -Mpreprocess Run preprocessor for Fortran files
• -Mrecursive Generate code to allow recursive subprograms
• -Mstandard Check standard conformance
• -Msave Assume all variables have SAVE attribute
• -module path to module file (-I also works)
• -Mallocatable=95 Select Fortran 95 semantics for assignments to allocatable objects (Default)
• -Mallocatable=03 Select Fortran 03 semantics for assignments to allocatable objects
• -static-flang-libs Link using static Flang libraries
• -M[no]daz Treat denormalized numbers as zero
• -M[no]flushz Set SSE to flush-to-zero mode
• -Mcache_align Align large objects on cache-line boundaries
• -M[no]fprelaxed This option is ignored
• -fdefault-integer-8 Treat INTEGER and LOGICAL as INTEGER8 and LOGICAL8
• -fdefault-real-8 Treat REAL as REAL*8
• -i8 Treat INTEGER and LOGICAL as INTEGER8 and LOGICAL8
• -r8 Treat REAL as REAL*8
• -fno-fortran-main Don't link in Fortran main

我编写了一个f90的hello world，来讲述flang的使用。

代码如下：

program main
write(*,*) "hello fortran world."
end program main 

使用flang产生IR文件

flang -emit-llvm helloworld.f90 -S -o helloworld.ll

我们也可以在此过程中加入 -O3选项，来进一步优化。

flang -O3 -emit-llvm helloworld.f90 -S -o helloworld.ll

生成bitcode

llvm-as helloworld.ll

生成.o文件

llc -filetype=obj helloworld.bc -o helloworld.o

产生可执行文件

flang helloworld.o -o helloworld

运行

./helloworld
hello fortran world

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