decodetree: Suppress redundant declaration warnings

We can tell that a decodetree input file is "secondary" when it
uses an argument set marked "!extern". This indicates that at
least one of the insn translation functions will have already
been declared by the "primary" input file, but given only the
secondary we cannot tell which.

Avoid redundant declaration warnings by suppressing them with pragmas.

Backports commit c692079597d98337b6f25deff7599afe39b2a468 from qemu

qemu/scripts/decodetree.py

@@ -165,6 +165,7 @@ arguments = {}
 formats = {}
 patterns = []
 allpatterns = []
+anyextern = False
 
 translate_prefix = 'trans'
 translate_scope = 'static '
@@ -616,12 +617,14 @@ def parse_arguments(lineno, name, toks):
     """Parse one argument set from TOKS at LINENO"""
     global arguments
     global re_ident
+    global anyextern
 
     flds = []
     extern = False
     for t in toks:
         if re_fullmatch('!extern', t):
             extern = True
+            anyextern = True
             continue
         if not re_fullmatch(re_ident, t):
             error(lineno, 'invalid argument set token "{0}"'.format(t))
@@ -1324,6 +1327,7 @@ def main():
     global insnmask
     global decode_function
     global variablewidth
+    global anyextern
 
     decode_scope = 'static '
 
@@ -1384,6 +1388,19 @@ def main():
     # A single translate function can be invoked for different patterns.
     # Make sure that the argument sets are the same, and declare the
     # function only once.
+    #
+    # If we're sharing formats, we're likely also sharing trans_* functions,
+    # but we can't tell which ones.  Prevent issues from the compiler by
+    # suppressing redundant declaration warnings.
+    if anyextern:
+        output("#ifdef CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE\n",
+               "# pragma GCC diagnostic push\n",
+               "# pragma GCC diagnostic ignored \"-Wredundant-decls\"\n",
+               "# ifdef __clang__\n"
+               "#  pragma GCC diagnostic ignored \"-Wtypedef-redefinition\"\n",
+               "# endif\n",
+               "#endif\n\n")
+
     out_pats = {}
     for i in allpatterns:
         if i.name in out_pats:
@@ -1395,6 +1412,11 @@ def main():
             out_pats[i.name] = i
     output('\n')
 
+    if anyextern:
+        output("#ifdef CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE\n",
+               "# pragma GCC diagnostic pop\n",
+               "#endif\n\n")
+
     for n in sorted(formats.keys()):
         f = formats[n]
         f.output_extract()