PR78736

[Prathamesh Kulkarni]

Hi,
This is a rebased patch on trunk for PR78736. The last time, it got
stuck, because of warning issues with libgfortran, for which I filed
PR91593. The patch relegates the warning to Wextra instead, which only
triggers (non-fatal) warnings in libgfortran/io/transfer.c, and
survives bootstrap+test on x86_64-unknown-linux-gnu. (Also IIRC, Wall
triggered several instances of the warning with allmodconfig kernel
build last time).
Is the patch OK to commit ?

Thanks,
Prathamesh
-------------- next part --------------
2019-08-29  Prathamesh Kulkarni  <prathamesh.kulkarni@linaro.org>

	* doc/invoke.texi: Document -Wenum-conversion.
	* c-family/c.opt (Wenum-conversion): New option.
	* c/c-typeck.c (convert_for_assignment): Handle Wenum-conversion.

testsuite/
	* gcc.dg/Wenum-conversion.c: New test-case.

diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
index 257cadfa5f1..601457b3762 100644
--- a/gcc/c-family/c.opt
+++ b/gcc/c-family/c.opt
@@ -534,6 +534,10 @@ Wenum-compare
 C ObjC C++ ObjC++ Var(warn_enum_compare) Init(-1) Warning LangEnabledBy(C ObjC,Wall || Wc++-compat)
 Warn about comparison of different enum types.
 
+Wenum-conversion
+C ObjC Var(warn_enum_conversion) Init(0) Warning LangEnabledBy(C ObjC,Wextra)
+Warn about implicit conversion of enum types.
+
 Werror
 C ObjC C++ ObjC++
 ; Documented in common.opt
diff --git a/gcc/c/c-typeck.c b/gcc/c/c-typeck.c
index 2bbf0e21fb9..d4e12eb93d1 100644
--- a/gcc/c/c-typeck.c
+++ b/gcc/c/c-typeck.c
@@ -6726,6 +6726,21 @@ convert_for_assignment (location_t location, location_t expr_loc, tree type,
 	  }
     }
 
+  if (warn_enum_conversion)
+    {
+      tree checktype = origtype != NULL_TREE ? origtype : rhstype;
+      if (checktype != error_mark_node
+	  && TREE_CODE (checktype) == ENUMERAL_TYPE
+	  && TREE_CODE (type) == ENUMERAL_TYPE
+	  && TYPE_MAIN_VARIANT (checktype) != TYPE_MAIN_VARIANT (type))
+       {
+	  gcc_rich_location loc (location);
+	  warning_at (&loc, OPT_Wenum_conversion,
+		      "implicit conversion from %qT to %qT",
+		      checktype, type);
+       }
+    }
+
   if (TYPE_MAIN_VARIANT (type) == TYPE_MAIN_VARIANT (rhstype))
     {
       warn_for_address_or_pointer_of_packed_member (type, orig_rhs);
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 549e043c67c..d497eb1f098 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -306,7 +306,8 @@ Objective-C and Objective-C++ Dialects}.
 -Wno-discarded-qualifiers  -Wno-discarded-array-qualifiers @gol
 -Wno-div-by-zero  -Wdouble-promotion @gol
 -Wduplicated-branches  -Wduplicated-cond @gol
--Wempty-body  -Wenum-compare  -Wno-endif-labels  -Wexpansion-to-defined @gol
+-Wempty-body  -Wenum-compare  -Wenum-conversion @gol
+-Wno-endif-labels  -Wexpansion-to-defined @gol
 -Werror  -Werror=*  -Wextra-semi  -Wfatal-errors @gol
 -Wfloat-equal  -Wformat  -Wformat=2 @gol
 -Wno-format-contains-nul  -Wno-format-extra-args  @gol
@@ -4430,6 +4431,7 @@ Options} and @ref{Objective-C and Objective-C++ Dialect Options}.
 -Wcomment  @gol
 -Wduplicate-decl-specifier @r{(C and Objective-C only)} @gol
 -Wenum-compare @r{(in C/ObjC; this is on by default in C++)} @gol
+-Wenum-conversion @r{in C/ObjC;} @gol
 -Wformat   @gol
 -Wint-in-bool-context  @gol
 -Wimplicit @r{(C and Objective-C only)} @gol
@@ -7002,6 +7004,12 @@ In C++ enumerated type mismatches in conditional expressions are also
 diagnosed and the warning is enabled by default.  In C this warning is 
 enabled by @option{-Wall}.
 
+@item -Wenum-conversion @r{(C, Objective-C only)}
+@opindex Wenum-conversion
+@opindex Wno-enum-conversion
+Warn when a value of enumerated type is implicitly converted to a 
+different enumerated type.  This warning is enabled by @option{-Wextra}.
+
 @item -Wextra-semi @r{(C++, Objective-C++ only)}
 @opindex Wextra-semi
 @opindex Wno-extra-semi
diff --git a/gcc/testsuite/gcc.dg/Wenum-conversion.c b/gcc/testsuite/gcc.dg/Wenum-conversion.c
new file mode 100644
index 00000000000..86033399b7d
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/Wenum-conversion.c
@@ -0,0 +1,20 @@
+/* { dg-do compile } */
+/* { dg-options "-Wenum-conversion" } */
+
+enum X { x1, x2 };
+enum Y { y1, y2 };
+
+enum X obj = y1;  /* { dg-warning "implicit conversion from .enum Y. to .enum X." } */
+enum Y obj2 = y1;
+
+enum X obj3;
+void foo()
+{
+  obj3 = y2; /* { dg-warning "implicit conversion from .enum Y. to .enum X." } */
+}
+
+void bar(enum X);
+void f(void)
+{
+  bar (y1); /* { dg-warning "implicit conversion from .enum Y. to .enum X." } */
+}