c-common.c (warn_div_by_zero): New.

	* c-common.c (warn_div_by_zero): New.
	* c-common.h (warn_div_by_zero): New.
	* c-decl.c (c_decode_option): Take it on the command line.
 	* c-typeck.c (build_binary_op): Warn about division by zero.
	* doc/invoke.texi: Document the new command line option, fix
	documentation of -Wmultichar.
 	* testsuite/gcc.dg/divbyzero.c: New tests.
 	* testsuite/gcc.dg/noncompile/20010524-1.c: Update.

From-SVN: r46439

gcc/ChangeLog

+2001-10-22  Neil Booth  <neil@daikokuya.demon.co.uk>
+
+	* c-common.c (warn_div_by_zero): New.
+	* c-common.h (warn_div_by_zero): New.
+	* c-decl.c (c_decode_option): Take it on the command line.
+ 	* c-typeck.c (build_binary_op): Warn about division by zero.
+	* doc/invoke.texi: Document the new command line option, fix
+	documentation of -Wmultichar.
+ 	* testsuite/gcc.dg/divbyzero.c: New tests.
+ 	* testsuite/gcc.dg/noncompile/20010524-1.c: Update.
+
 Tue Oct 23 15:30:23 CEST 2001  Jan Hubicka  <jh@suse.cz>
 
 	* i386.c (ix86_expand_int_movcc): Cleanup; use expand_simple_*op.

gcc/c-common.c

@@ -194,6 +194,9 @@ int flag_short_wchar;
 
 int warn_sequence_point;
 
+/* Nonzero means to warn about compile-time division by zero.  */
+int warn_div_by_zero = 1;
+
 /* The elements of `ridpointers' are identifier nodes for the reserved
    type names and storage classes.  It is indexed by a RID_... value.  */
 tree *ridpointers;

gcc/c-common.h

@@ -401,6 +401,9 @@ extern int warn_missing_format_attribute;
 
 extern int warn_pointer_arith;
 
+/* Nonzero means to warn about compile-time division by zero.  */
+extern int warn_div_by_zero;
+
 /* Nonzero means do some things the same way PCC does.  */
 
 extern int flag_traditional;

gcc/c-decl.c

@@ -750,6 +750,10 @@ c_decode_option (argc, argv)
     warn_multichar = 1;
   else if (!strcmp (p, "-Wno-multichar"))
     warn_multichar = 0;
+  else if (!strcmp (p, "-Wdiv-by-zero"))
+    warn_div_by_zero = 1;
+  else if (!strcmp (p, "-Wno-div-by-zero"))
+    warn_div_by_zero = 0;
   else if (!strcmp (p, "-Wunknown-pragmas"))
     /* Set to greater than 1, so that even unknown pragmas in system
        headers will be warned about.  */

gcc/c-typeck.c

@@ -1973,6 +1973,11 @@ build_binary_op (code, orig_op0, orig_op1, convert_p)
     case FLOOR_DIV_EXPR:
     case ROUND_DIV_EXPR:
     case EXACT_DIV_EXPR:
+      /* Floating point division by zero is a legitimate way to obtain
+	 infinities and NaNs.  */
+      if (warn_div_by_zero && skip_evaluation == 0 && integer_zerop (op1))
+	warning ("division by zero");
+
       if ((code0 == INTEGER_TYPE || code0 == REAL_TYPE
 	   || code0 == COMPLEX_TYPE)
 	  && (code1 == INTEGER_TYPE || code1 == REAL_TYPE
@@ -2026,6 +2031,9 @@ build_binary_op (code, orig_op0, orig_op1, convert_p)
 
     case TRUNC_MOD_EXPR:
     case FLOOR_MOD_EXPR:
+      if (warn_div_by_zero && skip_evaluation == 0 && integer_zerop (op1))
+	warning ("division by zero");
+
       if (code0 == INTEGER_TYPE && code1 == INTEGER_TYPE)
 	{
 	  /* Although it would be tempting to shorten always here, that loses

gcc/doc/invoke.texi

@@ -208,7 +208,7 @@ in the following sections.
 -fsyntax-only  -pedantic  -pedantic-errors @gol
 -w  -W  -Wall  -Waggregate-return @gol
 -Wcast-align  -Wcast-qual  -Wchar-subscripts  -Wcomment @gol
--Wconversion  -Wdisabled-optimization  -Werror @gol
+-Wconversion  -Wdisabled-optimization  -Wdiv-by-zero  -Werror @gol
 -Wfloat-equal  -Wformat  -Wformat=2 @gol
 -Wformat-nonliteral  -Wformat-security @gol
 -Wimplicit  -Wimplicit-int  @gol
@@ -1868,12 +1868,6 @@ int a[2][2] = @{ 0, 1, 2, 3 @};
 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
 @end smallexample
 
-@item -Wmultichar
-@opindex Wmultichar
-Warn if a multicharacter constant (@samp{'FOOF'}) is used.  Usually they
-indicate a typo in the user's code, as they have implementation-defined
-values, and should not be used in portable code.
-
 @item -Wparentheses
 @opindex Wparentheses
 Warn if parentheses are omitted in certain contexts, such
@@ -2129,6 +2123,22 @@ warnings about constructions that some users consider questionable, and
 that are easy to avoid (or modify to prevent the warning), even in
 conjunction with macros.
 
+@item -Wdiv-by-zero
+@opindex Wno-div-by-zero
+@opindex Wdiv-by-zero
+Warn about compile-time integer division by zero.  This is default.  To
+inhibit the warning messages, use @option{-Wno-div-by-zero}.  Floating
+point division by zero is not warned about, as it can be a legitimate
+way of obtaining infinities and NaNs.
+
+@item -Wmultichar
+@opindex Wno-multichar
+@opindex Wmultichar
+Warn if a multicharacter constant (@samp{'FOOF'}) is used.  This is
+default.  To inhibit the warning messages, use @option{-Wno-multichar}.
+Usually they indicate a typo in the user's code, as they have
+implementation-defined values, and should not be used in portable code.
+
 @item -Wsystem-headers
 @opindex Wsystem-headers
 @cindex warnings from system headers

gcc/testsuite/gcc.dg/divbyzero.c

+/* Copyright (C) 2001 Free Software Foundation, Inc.  */
+
+/* { dg-do compile } */
+
+/* Source: Neil Booth, Oct 22 2001.  PR 150 - warn about division by
+   zero.  */
+
+#define ZERO (4 - 6 + 2)
+
+int main (int argc, char *argv[])
+{
+  int w = argc % ZERO;		/* { dg-warning "division by zero" } */
+  int x = argc / 0;		/* { dg-warning "division by zero" } */
+  int y = argc / ZERO;		/* { dg-warning "division by zero" } */
+
+  double z = 0.0 / 0.0	;	/* { dg-bogus "division by zero" } */
+  w = (ZERO ? y / ZERO : x);	/* { dg-bogus "division by zero" } */
+  x = (ZERO ? argc % ZERO: x);  /* { dg-bogus "division by zero" } */
+
+  return 0;
+}

gcc/testsuite/gcc.dg/noncompile/20010524-1.c

 int i = 7 / 0; /* { dg-error "not constant" } */
-
+	/* { dg-warning "division by zero" "div by zero" { target *-*-* } 1 } */