Re: [google/gcc-4_8] Port -Wreal-conversion warning

[Sharad Singhai <singhai at google dot com>]

I reverted the earlier broken patch. I am including an updated patch
which warns only for real conversion, not for integral conversions. I
also updated the test case to include an integral conversion (int to
char) which doesn't emit the warning with the -Wreal-conversion flag.

Bootstrapped and tested on x86_64. Okay for google/gcc-4_8?

Thanks,
Sharad

2013-06-26    <lcwu@google.com>

        * doc/invoke.texi: Document new option -Wreal-conversion.
        * c-family/c.opt: Handle new option.
        * c-family/c-opts.c (c_common_post_options): Ditto.
        * c-family/c-common.c (conversion_warning): Ditto.

testsuite/ChangeLog:

        * testsuite/gcc.dg/Wreal-conversion-1.c: New test.
        * testsuite/g++.dg/warn/Wreal-conversion-1.C: Ditto.

Index: doc/invoke.texi
===================================================================
--- doc/invoke.texi (revision 200448)
+++ doc/invoke.texi (working copy)
@@ -237,7 +237,7 @@ Objective-C and Objective-C++ Dialects}.
 -Wno-attributes -Wno-builtin-macro-redefined @gol
 -Wc++-compat -Wc++11-compat -Wcast-align  -Wcast-qual  @gol
 -Wchar-subscripts -Wclobbered  -Wcomment @gol
--Wconversion  -Wcoverage-mismatch  -Wno-cpp  -Wno-deprecated  @gol
+-Wconversion -Wreal-conversion -Wcoverage-mismatch  -Wno-cpp
-Wno-deprecated  @gol
 -Wno-deprecated-declarations -Wdisabled-optimization  @gol
 -Wno-div-by-zero -Wdouble-promotion -Wempty-body  -Wenum-compare @gol
 -Wno-endif-labels -Werror  -Werror=* @gol
@@ -4452,6 +4452,12 @@ reference to them. Warnings about conversions betw
 unsigned integers are disabled by default in C++ unless
 @option{-Wsign-conversion} is explicitly enabled.

+@item -Wreal-conversion
+@opindex Wreal-conversion
+@opindex Wno-real-conversion
+Warn for implicit type conversions from real (@code{double} or @code{float})
+to integral values. This warning is also enabled by @option{-Wconversion}.
+
 @item -Wno-conversion-null @r{(C++ and Objective-C++ only)}
 @opindex Wconversion-null
 @opindex Wno-conversion-null
Index: c-family/c.opt
===================================================================
--- c-family/c.opt (revision 200448)
+++ c-family/c.opt (working copy)
@@ -677,6 +677,10 @@ Wsign-compare
 C ObjC C++ ObjC++ EnabledBy(Wextra)
 ;

+Wreal-conversion
+C ObjC C++ ObjC++ Var(warn_real_conversion) Init(-1) Warning
EnabledBy(Wconversion)
+Warn for implicit type conversions from real to integral values
+
 Wsign-conversion
 C ObjC C++ ObjC++ Var(warn_sign_conversion) LangEnabledBy(C ObjC,Wconversion)
 Warn for implicit type conversions between signed and unsigned integers
Index: c-family/c-opts.c
===================================================================
--- c-family/c-opts.c (revision 200448)
+++ c-family/c-opts.c (working copy)
@@ -876,6 +876,12 @@ c_common_post_options (const char **pfilename)
   if (warn_packed_bitfield_compat == -1)
     warn_packed_bitfield_compat = 1;

+  /* Enable warning for converting real values to integral values
+     when -Wconversion is specified (unless disabled through
+     -Wno-real-conversion).  */
+  if (warn_real_conversion == -1)
+    warn_real_conversion = warn_conversion;
+
   /* Special format checking options don't work without -Wformat; warn if
      they are used.  */
   if (!warn_format)
Index: c-family/c-common.c
===================================================================
--- c-family/c-common.c (revision 200448)
+++ c-family/c-common.c (working copy)
@@ -2665,12 +2665,22 @@ unsafe_conversion_p (tree type, tree expr, bool pr
 static void
 conversion_warning (tree type, tree expr)
 {
+  int warn_option;
   tree expr_type = TREE_TYPE (expr);
   location_t loc = EXPR_LOC_OR_HERE (expr);

-  if (!warn_conversion && !warn_sign_conversion)
+  if (!warn_conversion && !warn_sign_conversion && !warn_real_conversion)
     return;

+  /* When either type is a floating point type, warn with
+     -Wreal-conversion instead of -Wconversion (-Wreal-conversion is a
+     subset of -Wconversion that only warns for conversions of real
+     types to integral types).  */
+  warn_option = (warn_real_conversion
+ && (FLOAT_TYPE_P (type) || FLOAT_TYPE_P (expr_type)))
+    ? OPT_Wreal_conversion
+    : OPT_Wconversion;
+
   switch (TREE_CODE (expr))
     {
     case EQ_EXPR:
@@ -2689,14 +2699,14 @@ conversion_warning (tree type, tree expr)
  can hold the values 0 and -1) doesn't lose information - but
  it does change the value.  */
       if (TYPE_PRECISION (type) == 1 && !TYPE_UNSIGNED (type))
- warning_at (loc, OPT_Wconversion,
+ warning_at (loc, warn_option,
     "conversion to %qT from boolean expression", type);
       return;

     case REAL_CST:
     case INTEGER_CST:
       if (unsafe_conversion_p (type, expr, true))
- warning_at (loc, OPT_Wconversion,
+ warning_at (loc, warn_option,
     "conversion to %qT alters %qT constant value",
     type, expr_type);
       return;
@@ -2715,7 +2725,7 @@ conversion_warning (tree type, tree expr)

     default: /* 'expr' is not a constant.  */
       if (unsafe_conversion_p (type, expr, true))
- warning_at (loc, OPT_Wconversion,
+ warning_at (loc, warn_option,
     "conversion to %qT from %qT may alter its value",
     type, expr_type);
     }
Index: testsuite/g++.dg/warn/Wreal-conversion-1.C
===================================================================
--- testsuite/g++.dg/warn/Wreal-conversion-1.C (revision 0)
+++ testsuite/g++.dg/warn/Wreal-conversion-1.C (revision 0)
@@ -0,0 +1,25 @@
+// { dg-do compile }
+// { dg-options "-Wreal-conversion" }
+
+#include <stddef.h>
+
+int func1(int a) {
+  double f = a;
+  return f;           // { dg-warning "conversion to" }
+}
+
+double func3();
+
+void func2() {
+  double g = 3.14;
+  float f = 1.8f;
+  int t = g;          // { dg-warning "conversion to" }
+  bool b = g;
+  int p;
+  p = f;              // { dg-warning "conversion to" }
+  func1(g);           // { dg-warning "conversion to" }
+  char c = f;         // { dg-warning "conversion to" }
+  c = p;
+  int q;
+  q = func3();        // { dg-warning "conversion to" }
+}
Index: testsuite/gcc.dg/Wreal-conversion-1.c
===================================================================
--- testsuite/gcc.dg/Wreal-conversion-1.c (revision 0)
+++ testsuite/gcc.dg/Wreal-conversion-1.c (revision 0)
@@ -0,0 +1,24 @@
+// { dg-do compile }
+// { dg-options "-Wreal-conversion" }
+
+#include <stddef.h>
+
+int func1(int a) {
+  double f = a;
+  return f;           // { dg-warning "conversion to" }
+}
+
+double func3();
+
+void func2() {
+  double g = 3.14;
+  float f = 1.8f;
+  int t = g;          // { dg-warning "conversion to" }
+  int p;
+  p = f;              // { dg-warning "conversion to" }
+  func1(g);           // { dg-warning "conversion to" }
+  char c = f;         // { dg-warning "conversion to" }
+  c = p;
+  int q;
+  q = func3();        // { dg-warning "conversion to" }
+}