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

[Sharad Singhai <singhai at google dot com>]

Hi,

This patch forward ports the -Wreal-conversion warning to
google/gcc-4_8 branch (google ref 39133-p2). I tweaked the patch a
little bit to avoid printing duplicate warnings when both -Wconversion
and -Wreal-conversion are specified. Also, I trimmed the test case to
avoid testing for integer-to-integer narrowing conversions as this
warning is about real conversions.

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

Thanks,
Sharad

2013-06-24    <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: 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 +1,23 @@
+// { 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 = 3.2;
+  float f;
+  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" }
+  int q;
+  q = func3();        // { dg-warning "conversion to" }
+}
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 +1,24 @@
+// { 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 = 3.2;
+  float f;
+  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" }
+  int q;
+  q = func3();        // { dg-warning "conversion to" }
+}
Index: doc/invoke.texi
===================================================================
--- doc/invoke.texi (revision 200359)
+++ doc/invoke.texi (working copy)
@@ -193,7 +193,7 @@ in the following sections.
 -fno-default-inline  -fvisibility-inlines-hidden @gol
 -fvisibility-ms-compat @gol
 -fext-numeric-literals @gol
--Wabi  -Wconversion-null  -Wctor-dtor-privacy @gol
+-Wabi  -Wconversion-null -Wctor-dtor-privacy @gol
 -Wdelete-non-virtual-dtor -Wliteral-suffix -Wnarrowing @gol
 -Wnoexcept -Wnon-virtual-dtor  -Wreorder @gol
 -Weffc++  -Wstrict-null-sentinel @gol
@@ -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.
+
 @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 200359)
+++ 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
+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 200359)
+++ 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 200359)
+++ c-family/c-common.c (working copy)
@@ -2668,7 +2668,7 @@ conversion_warning (tree type, tree expr)
   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;

   switch (TREE_CODE (expr))
@@ -2715,9 +2715,17 @@ conversion_warning (tree type, tree expr)

     default: /* 'expr' is not a constant.  */
       if (unsafe_conversion_p (type, expr, true))
- warning_at (loc, OPT_Wconversion,
-    "conversion to %qT from %qT may alter its value",
-    type, expr_type);
+      {
+        /* Do not print the same warning twice. */
+        bool printed =
+            warning_at (loc, OPT_Wreal_conversion,
+                        "conversion to %qT from %qT may alter its value",
+                        type, expr_type);
+        if (!printed)
+          warning_at (loc, OPT_Wconversion,
+                      "conversion to %qT from %qT may alter its value",
+                      type, expr_type);
+      }
     }
 }