[Flang][Driver] Enable gpulibc/nogpulibc options for Flang, which allows linking of GPU LIBC for the fortran and OpenMP runtime (#77135)

This patch seeks to add the -gpulibc and -nogpulibc for Flang, which
allows the linking of the GPU libc library, this allows the use of
memcpy and other useful library functions for GPU.

In particular, this allows the Fortran runtime (written in C++) to be
compiled for offload and then linked against the GPU LIBC library via
this option to resolve memcpy and other C library functions that the
fortran runtime depends on for AMD GPU devices (and likely other GPU
devices).

This is the current method I've tested and found to be able to utilise
the Fortran runtime when compiled for AMD GPU, albeit it requires
compiling libc for GPU and then the Fortran runtime for GPU, so not
particularly straight forward or user friendly yet.

Activating this option will allow the subset of C functions to also be
utilised for GPU in other C/C++ based Fortran libraries if any are made
when linking against GPU libc.

Author: agozillon

clang/include/clang/Driver/Options.td

@@ -5200,9 +5200,9 @@ def nogpulib : Flag<["-"], "nogpulib">, MarshallingInfoFlag<LangOpts<"NoGPULib">
   Visibility<[ClangOption, CC1Option]>,
   HelpText<"Do not link device library for CUDA/HIP device compilation">;
 def : Flag<["-"], "nocudalib">, Alias<nogpulib>;
-def gpulibc : Flag<["-"], "gpulibc">, Visibility<[ClangOption, CC1Option]>,
+def gpulibc : Flag<["-"], "gpulibc">, Visibility<[ClangOption, CC1Option, FlangOption, FC1Option]>,
   HelpText<"Link the LLVM C Library for GPUs">;
-def nogpulibc : Flag<["-"], "nogpulibc">, Visibility<[ClangOption, CC1Option]>;
+def nogpulibc : Flag<["-"], "nogpulibc">, Visibility<[ClangOption, CC1Option, FlangOption, FC1Option]>;
 def nodefaultlibs : Flag<["-"], "nodefaultlibs">;
 def nodriverkitlib : Flag<["-"], "nodriverkitlib">;
 def nofixprebinding : Flag<["-"], "nofixprebinding">;

flang/test/Driver/driver-help-hidden.f90

@@ -108,6 +108,7 @@
 ! CHECK-NEXT: -fxor-operator          Enable .XOR. as a synonym of .NEQV.
 ! CHECK-NEXT: -gline-directives-only  Emit debug line info directives only
 ! CHECK-NEXT: -gline-tables-only      Emit debug line number tables only
+! CHECK-NEXT: -gpulibc                Link the LLVM C Library for GPUs
 ! CHECK-NEXT: -g                      Generate source-level debug information
 ! CHECK-NEXT: --help-hidden           Display help for hidden options
 ! CHECK-NEXT: -help                   Display available options

flang/test/Driver/driver-help.f90

@@ -94,6 +94,7 @@
 ! HELP-NEXT: -fxor-operator          Enable .XOR. as a synonym of .NEQV.
 ! HELP-NEXT: -gline-directives-only  Emit debug line info directives only
 ! HELP-NEXT: -gline-tables-only      Emit debug line number tables only
+! HELP-NEXT: -gpulibc                Link the LLVM C Library for GPUs
 ! HELP-NEXT: -g                      Generate source-level debug information
 ! HELP-NEXT: --help-hidden           Display help for hidden options
 ! HELP-NEXT: -help                   Display available options
@@ -228,6 +229,7 @@
 ! HELP-FC1-NEXT: -fversion-loops-for-stride
 ! HELP-FC1-NEXT:                         Create unit-strided versions of loops
 ! HELP-FC1-NEXT: -fxor-operator          Enable .XOR. as a synonym of .NEQV.
+! HELP-FC1-NEXT: -gpulibc                Link the LLVM C Library for GPUs
 ! HELP-FC1-NEXT: -help                   Display available options
 ! HELP-FC1-NEXT: -init-only              Only execute frontend initialization
 ! HELP-FC1-NEXT: -I <dir>                Add directory to the end of the list of include search paths

flang/test/Driver/omp-driver-offload.f90

@@ -169,3 +169,16 @@
 ! RUN: -fopenmp-host-ir-file-path non-existant-file.bc \
 ! RUN: | FileCheck %s --check-prefix=HOST-IR-MISSING
 ! HOST-IR-MISSING: error: provided host compiler IR file 'non-existant-file.bc' is required to generate code for OpenMP target regions but cannot be found
+
+! Check that `-gpulibc` includes the LLVM C libraries for the GPU.
+! RUN:   %flang -### --target=x86_64-unknown-linux-gnu -fopenmp  \
+! RUN:      --offload-arch=gfx90a --offload-arch=sm_52 \
+! RUN:      -gpulibc %s 2>&1 \
+! RUN:   | FileCheck --check-prefix=LIBC-GPU %s
+! LIBC-GPU: "-lcgpu"{{.*}}"-lmgpu"
+
+! RUN:   %flang -### --target=x86_64-unknown-linux-gnu -fopenmp  \
+! RUN:      --offload-arch=gfx90a --offload-arch=sm_52 \
+! RUN:      -nogpulibc %s 2>&1 \
+! RUN:   | FileCheck --check-prefix=NO-LIBC-GPU %s
+! NO-LIBC-GPU-NOT: "-lcgpu"{{.*}}"-lmgpu"