driver: Forward '-lgfortran', '-lm' to offloading compilation

..., so that users don't manually need to specify
'-foffload-options=-lgfortran', '-foffload-options=-lm' in addition to
'-lgfortran', '-lm' (specified manually, or implicitly by the driver).

	gcc/
	* gcc.cc (driver_handle_option): Forward host '-lgfortran', '-lm'
	to offloading compilation.
	* config/gcn/mkoffload.cc (main): Adjust.
	* config/nvptx/mkoffload.cc (main): Likewise.
	* doc/invoke.texi (foffload-options): Update example.
	libgomp/
	* testsuite/libgomp.fortran/fortran.exp (lang_link_flags): Don't
	set.
	* testsuite/libgomp.oacc-fortran/fortran.exp (lang_link_flags):
	Likewise.
	* testsuite/libgomp.c/simd-math-1.c: Remove
	'-foffload-options=-lm'.
	* testsuite/libgomp.fortran/fortran-torture_execute_math.f90:
	Likewise.
	* testsuite/libgomp.oacc-fortran/fortran-torture_execute_math.f90:
	Likewise.

gcc/config/gcn/mkoffload.cc

@@ -946,6 +946,18 @@ main (int argc, char **argv)
       else if (startswith (argv[i], STR))
 	gcn_stack_size = atoi (argv[i] + strlen (STR));
 #undef STR
+      /* Translate host into offloading libraries.  */
+      else if (strcmp (argv[i], "-l_GCC_gfortran") == 0
+	       || strcmp (argv[i], "-l_GCC_m") == 0)
+	{
+	  /* Elide '_GCC_'.  */
+	  size_t i_dst = strlen ("-l");
+	  size_t i_src = strlen ("-l_GCC_");
+	  char c;
+	  do
+	    c = argv[i][i_dst++] = argv[i][i_src++];
+	  while (c != '\0');
+	}
     }
 
   if (!(fopenacc ^ fopenmp))

gcc/config/nvptx/mkoffload.cc

@@ -649,6 +649,18 @@ main (int argc, char **argv)
       else if (strcmp (argv[i], "-dumpbase") == 0
 	       && i + 1 < argc)
 	dumppfx = argv[++i];
+      /* Translate host into offloading libraries.  */
+      else if (strcmp (argv[i], "-l_GCC_gfortran") == 0
+	       || strcmp (argv[i], "-l_GCC_m") == 0)
+	{
+	  /* Elide '_GCC_'.  */
+	  size_t i_dst = strlen ("-l");
+	  size_t i_src = strlen ("-l_GCC_");
+	  char c;
+	  do
+	    c = argv[i][i_dst++] = argv[i][i_src++];
+	  while (c != '\0');
+	}
     }
   if (!(fopenacc ^ fopenmp))
     fatal_error (input_location, "either %<-fopenacc%> or %<-fopenmp%> "

gcc/doc/invoke.texi

@@ -2716,9 +2716,8 @@ the @option{-foffload-options=@var{target-list}=@var{options}} form.  The
 Typical command lines are
 
 @smallexample
--foffload-options=-lgfortran -foffload-options=-lm
--foffload-options="-lgfortran -lm" -foffload-options=nvptx-none=-latomic
--foffload-options=amdgcn-amdhsa=-march=gfx906 -foffload-options=-lm
+-foffload-options='-fno-math-errno -ffinite-math-only' -foffload-options=nvptx-none=-latomic
+-foffload-options=amdgcn-amdhsa=-march=gfx906 -foffload-options=-O3
 @end smallexample
 
 @opindex fopenacc

gcc/gcc.cc

@@ -47,6 +47,9 @@ compilation is specified by a string called a "spec".  */
 #include "opts-jobserver.h"
 #include "common/common-target.h"
 
+#ifndef MATH_LIBRARY
+#define MATH_LIBRARY "m"
+#endif
 
 
 /* Manage the manipulation of env vars.
@@ -4117,6 +4120,48 @@ next_item:
     }
 }
 
+/* Forward certain options to offloading compilation.  */
+
+static void
+forward_offload_option (size_t opt_index, const char *arg, bool validated)
+{
+  switch (opt_index)
+    {
+    case OPT_l:
+      /* Use a '_GCC_' prefix and standard name ('-l_GCC_m' irrespective of the
+	 host's 'MATH_LIBRARY', for example), so that the 'mkoffload's can tell
+	 this has been synthesized here, and translate/drop as necessary.  */
+      /* Note that certain libraries ('-lc', '-lgcc', '-lgomp', for example)
+	 are injected by default in offloading compilation, and therefore not
+	 forwarded here.  */
+      /* GCC libraries.  */
+      if (/* '-lgfortran' */ strcmp (arg, "gfortran") == 0 )
+	save_switch (concat ("-foffload-options=-l_GCC_", arg, NULL),
+		     0, NULL, validated, true);
+      /* Other libraries.  */
+      else
+	{
+	  /* The case will need special consideration where on the host
+	     '!need_math', but for offloading compilation still need
+	     '-foffload-options=-l_GCC_m'.  The problem is that we don't get
+	     here anything like '-lm', because it's not synthesized in
+	     'gcc/fortran/gfortranspec.cc:lang_specific_driver', for example.
+	     Generally synthesizing '-foffload-options=-l_GCC_m' etc. in the
+	     language specific drivers is non-trivial, needs very careful
+	     review of their options handling.  However, this issue is not
+	     actually relevant for the current set of supported host/offloading
+	     configurations.  */
+	  int need_math = (MATH_LIBRARY[0] != '\0');
+	  if (/* '-lm' */ (need_math && strcmp (arg, MATH_LIBRARY) == 0))
+	    save_switch ("-foffload-options=-l_GCC_m",
+			 0, NULL, validated, true);
+	}
+      break;
+    default:
+      gcc_unreachable ();
+    }
+}
+
 /* Handle a driver option; arguments and return value as for
    handle_option.  */
 
@@ -4375,6 +4420,17 @@ driver_handle_option (struct gcc_options *opts,
       /* POSIX allows separation of -l and the lib arg; canonicalize
 	 by concatenating -l with its arg */
       add_infile (concat ("-l", arg, NULL), "*");
+
+      /* Forward to offloading compilation '-l[...]' flags for standard,
+	 well-known libraries.  */
+      /* Doing this processing here means that we don't get to see libraries
+	 injected via specs, such as '-lquadmath' injected via
+	 '[build]/[target]/libgfortran/libgfortran.spec'.  However, this issue
+	 is not actually relevant for the current set of host/offloading
+	 configurations.  */
+      if (ENABLE_OFFLOADING)
+	forward_offload_option (opt_index, arg, validated);
+
       do_save = false;
       break;
 

libgomp/testsuite/libgomp.c/simd-math-1.c

@@ -4,7 +4,6 @@
 /* { dg-do run } */
 /* { dg-options "-O2 -ftree-vectorize -fno-math-errno" } */
 /* { dg-additional-options -foffload-options=amdgcn-amdhsa=-mstack-size=3000000 { target offload_target_amdgcn } } */
-/* { dg-additional-options -foffload-options=-lm } */
 
 #undef PRINT_RESULT
 #define VERBOSE 0

libgomp/testsuite/libgomp.fortran/fortran-torture_execute_math.f90

@@ -1,4 +1,3 @@
 ! { dg-do run }
-! { dg-additional-options -foffload-options=-lm }
 
 include '../../../gcc/testsuite/gfortran.fortran-torture/execute/math.f90'

libgomp/testsuite/libgomp.fortran/fortran.exp

@@ -28,7 +28,6 @@ if { $blddir != "" } {
     set lang_source_re {^.*\.[fF](|90|95|03|08)$}
     set lang_include_flags "-fintrinsic-modules-path=${blddir}"
 }
-set lang_link_flags "-foffload=-lgfortran"
 lappend ALWAYS_CFLAGS "compiler=$GFORTRAN_UNDER_TEST"
 
 # Initialize dg.
@@ -63,7 +62,6 @@ if { $blddir != "" } {
     unset libquadmath_library_path
     unset lang_library_paths
 }
-unset lang_link_flags
 
 # All done.
 dg-finish

libgomp/testsuite/libgomp.oacc-fortran/fortran-torture_execute_math.f90

@@ -1,5 +1,4 @@
 ! { dg-do run }
 !TODO { dg-prune-output {using 'vector_length \(32\)', ignoring 1} }
-! { dg-additional-options -foffload-options=-lm }
 
 include '../../../gcc/testsuite/gfortran.fortran-torture/execute/math.f90'

libgomp/testsuite/libgomp.oacc-fortran/fortran.exp

@@ -30,7 +30,6 @@ if { $blddir != "" } {
     set lang_source_re {^.*\.[fF](|90|95|03|08)$}
     set lang_include_flags "-fintrinsic-modules-path=${blddir}"
 }
-set lang_link_flags "-foffload=-lgfortran"
 lappend ALWAYS_CFLAGS "compiler=$GFORTRAN_UNDER_TEST"
 
 # Initialize dg.
@@ -113,7 +112,6 @@ if { $blddir != "" } {
     unset libquadmath_library_path
     unset lang_library_paths
 }
-unset lang_link_flags
 
 # All done.
 dg-finish