[PATCH] fortran: Enable target preprocessor macros with -cpp [PR42954]

The Fortran preprocessor has never defined target-specific macros such as
__linux__, __unix__, __ELF__, __x86_64__, or __amd64__ that the C
preprocessor provides.  This was caused by the TARGET_OS_CPP_BUILTINS,
TARGET_OBJFMT_CPP_BUILTINS, and TARGET_CPU_CPP_BUILTINS hooks being
disabled since 2008 (marked as "Pandora's Box") because several target
config headers use C-family-only functions.

Fix by providing Fortran-compatible local helpers for
builtin_define_std, builtin_define_with_value, and
builtin_define_with_int_value (which in the C frontend live in
c-family/c-cppbuiltin.cc and use the C-family-only globals parse_in
and flag_iso), plus wrapper macros for c_dialect_cxx, flag_iso, and
other C-family identifiers referenced by target config headers.  This
allows TARGET_OS_CPP_BUILTINS and TARGET_OBJFMT_CPP_BUILTINS to
execute in the Fortran frontend.

Unlike the C frontend default (flag_iso=0, GNU extensions mode), the
Fortran wrapper sets flag_iso=1 to suppress user-namespace macros like
bare "unix" and "linux" that would conflict with Fortran identifiers.
Only the reserved-namespace forms (__unix__, __linux__, etc.) are
defined.  Fortran has no -std=cNN equivalent to control this, so the
conservative choice avoids silent identifier replacement.

For TARGET_CPU_CPP_BUILTINS, which on most architectures expands to a
function in a C-family-only object file (e.g., ix86_target_macros in
i386-c.cc), provide an x86 implementation directly in fortran/cpp.cc
that covers architecture identification and float-size macros.
ISA feature macros (__SSE__, __AVX__, etc.) are not included; if
needed, they could be factored out of i386-c.cc into a shared object.

Remove the dead __attribute__((target(...))) block from
gfortran.dg/gomp/declare-variant-10.f90: it was guarded by
#if defined(__x86_64__) which was previously always false because
gfortran never defined these macros, and gfortran does not support
C-style __attribute__ syntax.

Co-authored-by: Kai Tietz <[email protected]>

	PR fortran/42954

gcc/fortran/ChangeLog:

	* cpp.cc (gfc_builtin_define_std): New helper mirroring
	builtin_define_std from c-family/c-cppbuiltin.cc.
	(gfc_builtin_define_with_value): New helper mirroring
	builtin_define_with_value from c-family/c-cppbuiltin.cc.
	(gfc_define_ix86_target_macros): New function providing x86 CPU
	identification macros for the Fortran preprocessor.
	(gfc_darwin_cpp_builtins): New function providing Darwin platform
	macros.
	(cpp_define_builtins): Remove Pandora's Box FIXME.  Add wrapper
	macros for C-family functions and variables used in target config
	headers.  Set flag_iso=1 to suppress bare-name macros.  Enable
	TARGET_OS_CPP_BUILTINS and TARGET_OBJFMT_CPP_BUILTINS.  Call
	gfc_define_ix86_target_macros on x86 targets.

gcc/testsuite/ChangeLog:

	* gfortran.dg/gomp/declare-variant-10.f90: Remove dead
	__attribute__((target)) block that is now exposed by newly
	defined target macros.
	* gfortran.dg/pr42954-linux.f90: New test.
	* gfortran.dg/pr42954-x86.f90: New test.

Signed-off-by: Christopher Albert <[email protected]>
---
 gcc/fortran/cpp.cc                            | 178 ++++++++++++++++--
 .../gfortran.dg/gomp/declare-variant-10.f90   |   3 -
 gcc/testsuite/gfortran.dg/pr42954-linux.f90   |  24 +++
 gcc/testsuite/gfortran.dg/pr42954-x86.f90     |  10 +
 4 files changed, 194 insertions(+), 21 deletions(-)
 create mode 100644 gcc/testsuite/gfortran.dg/pr42954-linux.f90
 create mode 100644 gcc/testsuite/gfortran.dg/pr42954-x86.f90

diff --git a/gcc/fortran/cpp.cc b/gcc/fortran/cpp.cc
index 6b5f136e4f3..ada1bc1a211 100644
--- a/gcc/fortran/cpp.cc
+++ b/gcc/fortran/cpp.cc
@@ -157,6 +157,126 @@ void pp_dir_change (cpp_reader *, const char *);
 static int dump_macro (cpp_reader *, cpp_hashnode *, void *);
 static void dump_queued_macros (cpp_reader *);
 
+/* Fortran-local helpers that mirror builtin_define_std,
+   builtin_define_with_value, and builtin_define_with_int_value from
+   c-family/c-cppbuiltin.cc.  Those functions use the C-family-only
+   globals parse_in and flag_iso, so they cannot be called directly
+   from the Fortran frontend.  */
+
+/* Given "unix", define __unix, __unix__, and (if DEFINE_USER) unix.  */
+
+static void
+gfc_builtin_define_std (cpp_reader *pfile, const char *macro,
+			bool define_user)
+{
+  size_t len = strlen (macro);
+  char *buff = (char *) alloca (len + 5);
+  char *p = buff + 2;
+  char *q = p + len;
+
+  memcpy (p, macro, len + 1);
+  if (!(*p == '_' && (p[1] == '_' || ISUPPER (p[1]))))
+    {
+      if (*p != '_')
+	*--p = '_';
+      if (p[1] != '_')
+	*--p = '_';
+    }
+  cpp_define (pfile, p);
+
+  if (p != buff + 2)
+    {
+      if (q[-1] != '_')
+	*q++ = '_';
+      if (q[-2] != '_')
+	*q++ = '_';
+      *q = '\0';
+      cpp_define (pfile, p);
+      if (define_user)
+	cpp_define (pfile, macro);
+    }
+}
+
+/* Define MACRO to EXPANSION; if IS_STR, quote the expansion.  */
+
+static void
+gfc_builtin_define_with_value (cpp_reader *pfile, const char *macro,
+			       const char *expansion, int is_str)
+{
+  size_t mlen = strlen (macro);
+  size_t elen = strlen (expansion);
+  char *buf = (char *) alloca (mlen + elen + 4);
+  if (is_str)
+    sprintf (buf, "%s=\"%s\"", macro, expansion);
+  else
+    sprintf (buf, "%s=%s", macro, expansion);
+  cpp_define (pfile, buf);
+}
+
+/* Provide x86 CPU identification macros for the Fortran preprocessor.
+   TARGET_CPU_CPP_BUILTINS() cannot be called directly because it expands
+   to ix86_target_macros() in i386-c.cc, which is only linked into
+   C-family frontends.  This covers architecture identification and
+   float-size macros.  ISA feature macros (__SSE__, __AVX__, etc.) and
+   arch/tune macros (__znver4__, __skylake__, etc.) from
+   ix86_target_macros_internal() are not included; if needed, they could
+   be factored out of i386-c.cc into a shared object.  */
+
+#ifdef TARGET_80387
+static void
+gfc_define_ix86_target_macros (cpp_reader *pfile)
+{
+  if (TARGET_64BIT)
+    {
+      cpp_assert (pfile, "cpu=x86_64");
+      cpp_assert (pfile, "machine=x86_64");
+      cpp_define (pfile, "__amd64");
+      cpp_define (pfile, "__amd64__");
+      cpp_define (pfile, "__x86_64");
+      cpp_define (pfile, "__x86_64__");
+      if (TARGET_X32)
+	{
+	  cpp_define (pfile, "_ILP32");
+	  cpp_define (pfile, "__ILP32__");
+	}
+    }
+  else
+    {
+      cpp_assert (pfile, "cpu=i386");
+      cpp_assert (pfile, "machine=i386");
+      gfc_builtin_define_std (pfile, "i386", false);
+      cpp_define (pfile, "_ILP32");
+      cpp_define (pfile, "__ILP32__");
+    }
+
+  if (!TARGET_80387)
+    cpp_define (pfile, "_SOFT_FLOAT");
+
+  if (TARGET_LONG_DOUBLE_64)
+    cpp_define (pfile, "__LONG_DOUBLE_64__");
+
+  if (TARGET_LONG_DOUBLE_128)
+    cpp_define (pfile, "__LONG_DOUBLE_128__");
+
+  cpp_define_formatted (pfile, "__SIZEOF_FLOAT80__=%d",
+			GET_MODE_SIZE (XFmode));
+  cpp_define (pfile, "__SIZEOF_FLOAT128__=16");
+}
+#endif
+
+/* Provide essential Darwin platform macros for the Fortran preprocessor.
+   The full darwin_cpp_builtins() in darwin-c.cc also defines
+   __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ and
+   __CONSTANT_CFSTRINGS__, but those depend on functions only linked
+   into C-family frontends.  */
+
+static void ATTRIBUTE_UNUSED
+gfc_darwin_cpp_builtins (cpp_reader *pfile)
+{
+  cpp_define (pfile, "__MACH__");
+  cpp_define (pfile, "__APPLE__");
+  gfc_builtin_define_with_value (pfile, "__APPLE_CC__", "1", false);
+}
 
 static void
 cpp_define_builtins (cpp_reader *pfile)
@@ -177,33 +297,55 @@ cpp_define_builtins (cpp_reader *pfile)
   if (flag_openmp)
     cpp_define (pfile, "_OPENMP=202111");
 
-  /* The defines below are necessary for the TARGET_* macros.
-
-     FIXME:  Note that builtin_define_std() actually is a function
-     in c-cppbuiltin.cc which uses flags undefined for Fortran.
-     Let's skip this for now. If needed, one needs to look into it
-     once more.  */
+  /* Wrapper macros for C-family identifiers used in target config
+     headers.  These allow TARGET_OS_CPP_BUILTINS and
+     TARGET_OBJFMT_CPP_BUILTINS to compile in the Fortran frontend.  */
 
 # define builtin_define(TXT) cpp_define (pfile, TXT)
-# define builtin_define_std(TXT)
+# define builtin_define_std(TXT) gfc_builtin_define_std (pfile, TXT, !flag_iso)
+# define builtin_define_with_value(MACRO, EXPANSION, IS_STR) \
+  gfc_builtin_define_with_value (pfile, MACRO, EXPANSION, IS_STR)
+# define builtin_define_with_int_value(MACRO, VALUE) \
+  cpp_define_formatted (pfile, "%s=" HOST_WIDE_INT_PRINT_DEC, \
+			MACRO, (HOST_WIDE_INT) (VALUE))
 # define builtin_assert(TXT) cpp_assert (pfile, TXT)
+# define c_dialect_cxx() 0
+# define c_dialect_objc() 0
+# define preprocessing_asm_p() 0
+# define preprocessing_trad_p() 0
+  /* Fortran has no -std=cNN flag to control this.  Set to 1 (ISO mode)
+     so that builtin_define_std() only defines reserved-namespace macros
+     like __unix__ and __linux__, not bare "unix" or "linux" which are
+     valid Fortran identifiers and would cause silent replacement.  */
+# define flag_iso 1
+# define flag_isoc94 0
+# define flag_isoc99 0
+# define flag_isoc11 0
+# define flag_isoc23 0
+# define darwin_cpp_builtins(PFILE) gfc_darwin_cpp_builtins (PFILE)
 
-  /* FIXME: Pandora's Box
-    Using the macros below results in multiple breakages:
-     - mingw will fail to compile this file as dependent macros
-       assume to be used in c-cppbuiltin.cc only. Further, they use
-       flags only valid/defined in C (same as noted above).
-       [config/i386/mingw32.h, config/i386/cygming.h]
-     - other platforms (not as popular) break similarly
-       [grep for 'builtin_define_with_int_value' in gcc/config/]
-
-  TARGET_CPU_CPP_BUILTINS ();
   TARGET_OS_CPP_BUILTINS ();
-  TARGET_OBJFMT_CPP_BUILTINS (); */
+  TARGET_OBJFMT_CPP_BUILTINS ();
+
+#ifdef TARGET_80387
+  gfc_define_ix86_target_macros (pfile);
+#endif
 
 #undef builtin_define
 #undef builtin_define_std
+#undef builtin_define_with_value
+#undef builtin_define_with_int_value
 #undef builtin_assert
+#undef c_dialect_cxx
+#undef c_dialect_objc
+#undef preprocessing_asm_p
+#undef preprocessing_trad_p
+#undef flag_iso
+#undef flag_isoc94
+#undef flag_isoc99
+#undef flag_isoc11
+#undef flag_isoc23
+#undef darwin_cpp_builtins
 }
 
 bool
diff --git a/gcc/testsuite/gfortran.dg/gomp/declare-variant-10.f90 b/gcc/testsuite/gfortran.dg/gomp/declare-variant-10.f90
index 0e0ab518010..115195e1194 100644
--- a/gcc/testsuite/gfortran.dg/gomp/declare-variant-10.f90
+++ b/gcc/testsuite/gfortran.dg/gomp/declare-variant-10.f90
@@ -64,9 +64,6 @@ contains
     call f18 ()	  ! { dg-final { scan-tree-dump-times "f18 \\\(\\\);" 1 "gimple" } } */
   end subroutine
 
-#if defined(__i386__) || defined(__x86_64__)
-  __attribute__((target ("avx512f,avx512bw")))
-#endif
   subroutine test2 ()
     !$omp target
       call f04 () ! { dg-final { scan-tree-dump-times "f03 \\\(\\\);" 1 "gimple" { target { { i?86-*-* x86_64-*-* } && { ! ilp32 } } } } }
diff --git a/gcc/testsuite/gfortran.dg/pr42954-linux.f90 b/gcc/testsuite/gfortran.dg/pr42954-linux.f90
new file mode 100644
index 00000000000..bd5efe7a237
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/pr42954-linux.f90
@@ -0,0 +1,24 @@
+! { dg-do preprocess { target *-*-linux* } }
+! { dg-options "-cpp" }
+!
+! PR fortran/42954 - target macros missing in gfortran -cpp
+
+#ifndef __linux__
+# error __linux__ not defined
+#endif
+
+#ifndef __linux
+# error __linux not defined
+#endif
+
+#ifndef __unix__
+# error __unix__ not defined
+#endif
+
+#ifndef __unix
+# error __unix not defined
+#endif
+
+#ifndef __ELF__
+# error __ELF__ not defined
+#endif
diff --git a/gcc/testsuite/gfortran.dg/pr42954-x86.f90 b/gcc/testsuite/gfortran.dg/pr42954-x86.f90
new file mode 100644
index 00000000000..0a3b7eac8a2
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/pr42954-x86.f90
@@ -0,0 +1,10 @@
+! { dg-do preprocess { target { i?86-*-* x86_64-*-* } } }
+! { dg-options "-cpp" }
+!
+! PR fortran/42954 - target macros missing in gfortran -cpp
+
+#if !defined(__i386__) && !defined(__i386) \
+    && !defined(__x86_64__) && !defined(__x86_64) \
+    && !defined(__amd64__) && !defined(__amd64)
+# error x86 target macros not defined
+#endif
-- 
2.53.0