c: Turn -Wincompatible-pointer-types into a permerror

The change to build_conditional_expr drops the downgrade
from a pedwarn to warning for builtins for C99 and later
language dialects.  It remains a warning in C89 mode (not
a permerror), as the -std=gnu89 -fno-permissive test shows.

gcc/

	* doc/invoke.texi (Warning Options): Document changes.

gcc/c/

	PR c/96284
	* c-typeck.cc (build_conditional_expr): Upgrade most pointer
	type mismatches to a permerror.
	(convert_for_assignment): Use permerror_opt and
	permerror_init for OPT_Wincompatible_pointer_types warnings.

gcc/testsuite/

	* gcc.dg/permerror-default.c (incompatible_pointer_types):
	Expect new permerror.
	* gcc.dg/permerror-gnu89-nopermissive.c
	(incompatible_pointer_types): Likewise.
	* gcc.dg/permerror-pedantic.c (incompatible_pointer_types):
	Likewise.
	* gcc.dg/permerror-system.c: Likewise.
	* gcc.dg/Wincompatible-pointer-types-2.c: Compile with
	-fpermissive due to expected errors.
	* gcc.dg/Wincompatible-pointer-types-5.c: New test.  Copied
	from gcc.dg/Wincompatible-pointer-types-2.c.  Expect errors.
	* gcc.dg/anon-struct-11.c: Compile with -fpermissive
	due to expected errors.
	* gcc.dg/anon-struct-11a.c: New test.  Copied from
	gcc.dg/anon-struct-11.c.  Expect errors.
	* gcc.dg/anon-struct-13.c: Compile with -fpermissive
	due to expected errors.
	* gcc.dg/anon-struct-13a.c: New test.  Copied from
	gcc.dg/anon-struct-13.c.  Expect errors.
	* gcc.dg/builtin-arith-overflow-4.c: Compile with -fpermissive
	due to expected errors.
	* gcc.dg/builtin-arith-overflow-4a.c: New test.  Copied from
	gcc.dg/builtin-arith-overflow-4.c.  Expect errors.
	* gcc.dg/c23-qual-4.c: Expect -Wincompatible-pointer-types errors.
	* gcc.dg/dfp/composite-type.c: Compile with -fpermissive
	due to expected errors.
	* gcc.dg/dfp/composite-type-2.c: New test.  Copied from
	gcc.dg/dfp/composite-type.c.  Expect errors.
	* gcc.dg/diag-aka-1.c: Compile with -fpermissive
	due to expected errors.
	* gcc.dg/diag-aka-1a.c: New test.  Copied from
	gcc.dg/diag-aka-1a.c.  Expect errors.
	* gcc.dg/enum-compat-1.c: Compile with -fpermissive
	due to expected errors.
	* gcc.dg/enum-compat-2.c: New test.  Copied from
	gcc.dg/enum-compat-1.c.  Expect errors.
	* gcc.dg/func-ptr-conv-1.c: Compile with -fpermissive
	due to expected errors.
	* gcc.dg/func-ptr-conv-2.c: New test.  Copied from
	gcc.dg/func-ptr-conv-1.c.  Expect errors.
	* gcc.dg/init-bad-7.c: Compile with -fpermissive
	due to expected errors.
	* gcc.dg/init-bad-7a.c: New test.  Copied from gcc.dg/init-bad-7.c.
	Expect errors.
	* gcc.dg/noncompile/incomplete-3.c (foo): Expect
	-Wincompatible-pointer-types error.
	* gcc.dg/param-type-mismatch-2.c (test8): Likewise.
	* gcc.dg/pointer-array-atomic.c: Compile with -fpermissive
	due to expected errors.
	* gcc.dg/pointer-array-atomic-2.c: New test.  Copied from
	gcc.dg/pointer-array-atomic.c.  Expect errors.
	* gcc.dg/pointer-array-quals-1.c (test): Expect
	-Wincompatible-pointer-types errors.
	* gcc.dg/transparent-union-1.c: Compile with -fpermissive
	due to expected errors.
	* gcc.dg/transparent-union-1a.c: New test.  Copied from
	gcc.dg/transparent-union-1.c.  Expect errors.
	* gcc.target/aarch64/acle/memtag_2a.c
	(test_memtag_warning_return_qualifier): Expect additional
	errors.
	* gcc.target/aarch64/sve/acle/general-c/load_2.c (f1): Likewise.
	* gcc.target/aarch64/sve/acle/general-c/load_ext_gather_offset_1.c
	(f1): Likewise.
	* gcc.target/aarch64/sve/acle/general-c/load_ext_gather_offset_2.c
	(f1): Likewise.
	* gcc.target/aarch64/sve/acle/general-c/load_ext_gather_offset_3.c
	(f1): Likewise.
	* gcc.target/aarch64/sve/acle/general-c/load_ext_gather_offset_4.c
	(f1): Likewise.
	* gcc.target/aarch64/sve/acle/general-c/load_ext_gather_offset_5.c
	(f1): Likewise.
	* gcc.target/aarch64/sve/acle/general-c/load_ext_gather_offset_restricted_1.c
	(f1): Likewise.
	* gcc.target/aarch64/sve/acle/general-c/load_ext_gather_offset_restricted_2.c
	(f1): Likewise.
	* gcc.target/aarch64/sve/acle/general-c/load_ext_gather_offset_restricted_3.c
	(f1): Likewise.
	* gcc.target/aarch64/sve/acle/general-c/load_ext_gather_offset_restricted_4.c
	(f1): Likewise.
	* gcc.target/aarch64/sve/acle/general-c/sizeless-1.c (f1): Likewise.
	* gcc.target/aarch64/sve/acle/general-c/sizeless-2.c (f1): Likewise.
	* gcc.target/aarch64/sve/acle/general-c/store_1.c (f1): Likewise.
	* gcc.target/aarch64/sve/acle/general-c/store_2.c (f1): Likewise.
	* gcc.target/aarch64/sve/acle/general-c/store_scatter_index_1.c
	(f1): Likewise.
	* gcc.target/aarch64/sve/acle/general-c/store_scatter_index_restricted_1.c
	(f1): Likewise.
	* gcc.target/aarch64/sve/acle/general-c/store_scatter_offset_2.c
	(f1): Likewise.
	* gcc.target/aarch64/sve/acle/general-c/store_scatter_offset_restricted_1.c
	(f1): Likewise.
	* gcc.target/aarch64/sve/acle/general/attributes_7.c
	(f1): Likewise.
	* gcc.target/i386/sse2-bfloat16-scalar-typecheck.c (footest):
	Expect -Wincompatible-pointer-types errors.
	* gcc.target/i386/vect-bfloat16-typecheck_1.c (footest): Likewise.
	* gcc.target/i386/vect-bfloat16-typecheck_2.c (footest): Likewise.

gcc/c/c-typeck.cc

@@ -5463,8 +5463,15 @@ build_conditional_expr (location_t colon_loc, tree ifexp, bool ifexp_bcp,
       else
 	{
 	  int qual = ENCODE_QUAL_ADDR_SPACE (as_common);
-	  if (emit_diagnostic (bltin1 && bltin2 ? DK_WARNING : DK_PEDWARN,
-			       colon_loc, OPT_Wincompatible_pointer_types,
+	  diagnostic_t kind = DK_PERMERROR;
+	  if (!flag_isoc99)
+	    /* This downgrade to a warning ensures that -std=gnu89
+	       -pedantic-errors does not flag these mismatches between
+	       builtins as errors (as DK_PERMERROR would).  ISO C99
+	       and later do not have implicit function declarations,
+	       so the mismatch cannot occur naturally there.  */
+	    kind = bltin1 && bltin2 ? DK_WARNING : DK_PEDWARN;
+	  if (emit_diagnostic (kind, colon_loc, OPT_Wincompatible_pointer_types,
 			       "pointer type mismatch "
 			       "in conditional expression"))
 	    {
@@ -7602,46 +7609,47 @@ convert_for_assignment (location_t location, location_t expr_loc, tree type,
 		auto_diagnostic_group d;
 		range_label_for_type_mismatch rhs_label (rhstype, type);
 		gcc_rich_location richloc (expr_loc, &rhs_label);
-		if (pedwarn (&richloc, OPT_Wincompatible_pointer_types,
-			     "passing argument %d of %qE from incompatible "
-			     "pointer type", parmnum, rname))
+		if (permerror_opt (&richloc, OPT_Wincompatible_pointer_types,
+				   "passing argument %d of %qE from "
+				   "incompatible pointer type",
+				   parmnum, rname))
 		  inform_for_arg (fundecl, expr_loc, parmnum, type, rhstype);
 	      }
 	      break;
 	    case ic_assign:
 	      if (bltin)
-		pedwarn (location, OPT_Wincompatible_pointer_types,
-			 "assignment to %qT from pointer to "
-			 "%qD with incompatible type %qT",
-			 type, bltin, rhstype);
+		permerror_opt (location, OPT_Wincompatible_pointer_types,
+			       "assignment to %qT from pointer to "
+			       "%qD with incompatible type %qT",
+			       type, bltin, rhstype);
 	      else
-		pedwarn (location, OPT_Wincompatible_pointer_types,
-			 "assignment to %qT from incompatible pointer type %qT",
-			 type, rhstype);
+		permerror_opt (location, OPT_Wincompatible_pointer_types,
+			       "assignment to %qT from incompatible pointer "
+			       "type %qT", type, rhstype);
 	      break;
 	    case ic_init:
 	    case ic_init_const:
 	      if (bltin)
-		pedwarn_init (location, OPT_Wincompatible_pointer_types,
-			      "initialization of %qT from pointer to "
-			      "%qD with incompatible type %qT",
-			      type, bltin, rhstype);
+		permerror_init (location, OPT_Wincompatible_pointer_types,
+				"initialization of %qT from pointer to "
+				"%qD with incompatible type %qT",
+				type, bltin, rhstype);
 	      else
-		pedwarn_init (location, OPT_Wincompatible_pointer_types,
-			      "initialization of %qT from incompatible "
-			      "pointer type %qT",
-			      type, rhstype);
+		permerror_init (location, OPT_Wincompatible_pointer_types,
+				"initialization of %qT from incompatible "
+				"pointer type %qT",
+				type, rhstype);
 	      break;
 	    case ic_return:
 	      if (bltin)
-		pedwarn (location, OPT_Wincompatible_pointer_types,
-			 "returning pointer to %qD of type %qT from "
-			 "a function with incompatible type %qT",
-			 bltin, rhstype, type);
+		permerror_opt (location, OPT_Wincompatible_pointer_types,
+			       "returning pointer to %qD of type %qT from "
+			       "a function with incompatible type %qT",
+			       bltin, rhstype, type);
 	      else
-		pedwarn (location, OPT_Wincompatible_pointer_types,
-			 "returning %qT from a function with incompatible "
-			 "return type %qT", rhstype, type);
+		permerror_opt (location, OPT_Wincompatible_pointer_types,
+			       "returning %qT from a function with "
+			       "incompatible return type %qT", rhstype, type);
 	      break;
 	    default:
 	      gcc_unreachable ();

gcc/doc/invoke.texi

@@ -6186,6 +6186,7 @@ that have their own flag:
 @gccoptlist{
 -Wimplicit-function-declaration @r{(C and Objective-C only)}
 -Wimplicit-int @r{(C and Objective-C only)}
+-Wincompatible-pointer-types @r{(C and Objective-C only)}
 -Wint-conversion @r{(C and Objective-C only)}
 -Wnarrowing @r{(C++)}
 -Wreturn-mismatch @r{(C and Objective-C only)}
@@ -8566,6 +8567,11 @@ types.  This warning is for cases not covered by @option{-Wno-pointer-sign},
 which warns for pointer argument passing or assignment with different
 signedness.
 
+By default, in C99 and later dialects of C, GCC treats this issue as an
+error.  The error can be downgraded to a warning using
+@option{-fpermissive} (along with certain other errors), or for this
+error alone, with @option{-Wno-error=incompatible-pointer-types}.
+
 This warning is upgraded to an error by @option{-pedantic-errors}.
 
 @opindex Wno-int-conversion

gcc/testsuite/gcc.dg/Wincompatible-pointer-types-2.c

@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "" } */
+/* { dg-options "-fpermissive" } */
 
 void *
 f1 (int flag, int *a, long *b)

gcc/testsuite/gcc.dg/Wincompatible-pointer-types-5.c

@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+/* { dg-options "" } */
+
+void *
+f1 (int flag, int *a, long *b)
+{
+  return flag ? a : b; /* { dg-error "pointer type mismatch in conditional expression \\\[-Wincompatible-pointer-types\\\]" } */
+  /* { dg-note "first expression has type 'int \\*'" "" { target *-*-* } .-1 } */
+  /* { dg-note "second expression has type 'long int \\*'" "" { target *-*-* } .-2 } */
+}

gcc/testsuite/gcc.dg/anon-struct-11.c

@@ -1,8 +1,7 @@
 /* { dg-do compile } */
 
-/* No special options--in particular, turn off the default
-   -pedantic-errors option.  */
-/* { dg-options "" } */
+/* Also turn off the default -pedantic-errors option.  */
+/* { dg-options "-fpermissive" } */
 
 /* When not using -fplan9-extensions, we don't support automatic
    conversion of pointer types, and we don't support referring to a

gcc/testsuite/gcc.dg/anon-struct-11a.c

@@ -0,0 +1,111 @@
+/* { dg-do compile } */
+
+/* No special options--in particular, turn off the default
+   -pedantic-errors option.  */
+/* { dg-options "" } */
+
+/* When not using -fplan9-extensions, we don't support automatic
+   conversion of pointer types, and we don't support referring to a
+   typedef name directly.  */
+
+extern void exit (int);
+extern void abort (void);
+
+struct A { char a; };
+
+struct B {
+  char b;
+  struct A;		/* { dg-warning "does not declare anything" } */
+  char c;
+};
+
+void
+f1 (struct A *p)	/* { dg-message "expected" } */
+{
+  p->a = 1;
+}
+
+void
+test1 (void)
+{
+  struct B b;
+  struct A *p;
+
+  b.b = 2;
+  b.c = 3;
+  f1 (&b);		/* { dg-error "incompatible pointer type" } */
+  if (b.a != 1)		/* { dg-error "no member" } */
+    abort ();
+  if (b.b != 2 || b.c != 3)
+    abort ();
+  p = &b;		/* { dg-error "incompatible pointer type" } */
+  if (p->a != 1)
+    abort ();
+}
+
+typedef struct { char d; } D;
+
+struct E {
+  char b;
+  struct F { char f; };	/* { dg-warning "does not declare anything" } */
+  char c;
+  union {
+    D;			/* { dg-warning "does not declare anything" } */
+  };
+  char e;
+};
+
+void
+f2 (struct F *p)	/* { dg-message "expected" } */
+{
+  p->f = 6;
+}
+
+void
+f3 (D *p)		/* { dg-message "expected" } */
+{
+  p->d = 4;
+}
+
+void
+f4 (D d)
+{
+}
+
+void
+test2 (void)
+{
+  struct E e;
+  struct F *pf;
+  D *pd;
+  D d;
+
+  e.b = 2;
+  e.c = 3;
+  e.e = 5;
+  f2 (&e);		/* { dg-error "incompatible pointer type" } */
+  f3 (&e);		/* { dg-error "incompatible pointer type" } */
+  if (e.d != 4)		/* { dg-error "no member" } */
+    abort ();
+  if (e.f != 6)		/* { dg-error "no member" } */
+    abort ();
+  if (e.b != 2 || e.c != 3 || e.e != 5)
+    abort ();
+  pf = &e;		/* { dg-error "incompatible pointer type" } */
+  if (pf->f != 6)
+    abort ();
+  pd = &e;		/* { dg-error "incompatible pointer type" } */
+  if (pd->d != 4)
+    abort ();
+  d = e.D;		/* { dg-error "no member" } */
+  f3 (&e.D);		/* { dg-error "no member" } */
+  f4 (e.D);		/* { dg-error "no member" } */
+}
+
+int
+main ()
+{
+  test1 ();
+  test2 ();
+  exit (0);
+}

gcc/testsuite/gcc.dg/anon-struct-13.c

@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-fplan9-extensions" } */
+/* { dg-options "-fpermissive -fplan9-extensions" } */
 
 /* Test for ambiguity when using the Plan 9 extensions.  */
 

gcc/testsuite/gcc.dg/anon-struct-13a.c

@@ -0,0 +1,76 @@
+/* { dg-do compile } */
+/* { dg-options "-fplan9-extensions" } */
+
+/* Test for ambiguity when using the Plan 9 extensions.  */
+
+struct A {
+  char a;		/* { dg-error "duplicate member" } */
+};
+
+struct B
+{
+  struct A;
+  struct A;
+};
+
+char
+f1 (struct B *p)
+{
+  return p->a;		/* { dg-error "no member" } */
+}
+
+void
+f2 (struct A *p)	/* { dg-message "expected" } */
+{
+}
+
+void
+f3 (struct B *p)
+{
+  f2 (p);		/* { dg-error "incompatible pointer type" } */
+}
+
+struct C
+{
+  char c;		/* { dg-error "duplicate member" } */
+};
+
+struct D
+{
+  struct C;
+};
+
+struct E
+{
+  struct C;
+  struct D;
+};
+
+char
+f4 (struct E *p)
+{
+  return p->c;		/* { dg-error "no member" } */
+}
+
+void
+f6 (struct C *p)	/* { dg-message "expected" } */
+{
+}
+
+void
+f7 (struct E *p)
+{
+  f6 (p);		/* { dg-error "incompatible pointer type" } */
+}
+
+struct A
+f8 (struct B *p)
+{
+  return p->A;		/* { dg-error "no member" } */
+}
+
+struct C
+f9 (struct E *p)
+{
+  return p->C;		/* { dg-error "no member" } */
+}

gcc/testsuite/gcc.dg/builtin-arith-overflow-4.c

@@ -1,6 +1,6 @@
 /* PR c/90628 */
 /* { dg-do compile } */
-/* { dg-options "" } */
+/* { dg-options "-fpermissive" } */
 
 _Atomic int a = 1, b = 2, c = 3;
 _Atomic long d = 4, e = 5, f = 6;

gcc/testsuite/gcc.dg/builtin-arith-overflow-4a.c

@@ -0,0 +1,43 @@
+/* PR c/90628 */
+/* { dg-do compile } */
+/* { dg-options "" } */
+
+_Atomic int a = 1, b = 2, c = 3;
+_Atomic long d = 4, e = 5, f = 6;
+_Atomic long long g = 7, h = 8, i = 9;
+
+void
+f1 ()
+{
+  __builtin_add_overflow (a, b, &c);	/* { dg-error "argument 3 in call to function '__builtin_add_overflow' has pointer to '_Atomic' type" } */
+}
+
+void
+f2 ()
+{
+  __builtin_sub_overflow (d, e, &f);	/* { dg-error "argument 3 in call to function '__builtin_sub_overflow' has pointer to '_Atomic' type" } */
+}
+
+void
+f3 ()
+{
+  __builtin_mul_overflow (g, h, &i);	/* { dg-error "argument 3 in call to function '__builtin_mul_overflow' has pointer to '_Atomic' type" } */
+}
+
+void
+f4 ()
+{
+  __builtin_sadd_overflow (a, b, &c);	/* { dg-error "passing argument 3 of '__builtin_sadd_overflow' from incompatible pointer type" } */
+}
+
+void
+f5 ()
+{
+  __builtin_ssubl_overflow (d, e, &f);	/* { dg-error "passing argument 3 of '__builtin_ssubl_overflow' from incompatible pointer type" } */
+}
+
+void
+f6 ()
+{
+  __builtin_smulll_overflow (g, h, &i);	/* { dg-error "passing argument 3 of '__builtin_smulll_overflow' from incompatible pointer type" } */
+}