[clang][Sema] Subclass -Wshorten-64-to-32 under `-Wimplicit-int-con…

…version` (#80814)

Although "implicit int conversions" is supposed to be a superset
containing the more specific "64-to-32" case, previously they were a
disjoint set, only enabled in common in the much larger `-Wconversion`.

clang/docs/ReleaseNotes.rst

@@ -149,7 +149,12 @@ Improvements to Clang's diagnostics
   prints.
 
 - Clang now diagnoses member template declarations with multiple declarators.
-- Clang now diagnoses use of the ``template`` keyword after declarative nested name specifiers.
+
+- Clang now diagnoses use of the ``template`` keyword after declarative nested
+  name specifiers.
+
+- The ``-Wshorten-64-to-32`` diagnostic is now grouped under ``-Wimplicit-int-conversion`` instead
+   of ``-Wconversion``. Fixes `#69444 <https://github.com/llvm/llvm-project/issues/69444>`_.
 
 Improvements to Clang's time-trace
 ----------------------------------

clang/include/clang/Basic/DiagnosticGroups.td

@@ -108,8 +108,10 @@ def EnumConversion : DiagGroup<"enum-conversion",
                                 EnumCompareConditional]>;
 def ObjCSignedCharBoolImplicitIntConversion :
   DiagGroup<"objc-signed-char-bool-implicit-int-conversion">;
+def Shorten64To32 : DiagGroup<"shorten-64-to-32">;
 def ImplicitIntConversion : DiagGroup<"implicit-int-conversion",
-                                     [ObjCSignedCharBoolImplicitIntConversion]>;
+                                     [Shorten64To32,
+                                      ObjCSignedCharBoolImplicitIntConversion]>;
 def ImplicitConstIntFloatConversion : DiagGroup<"implicit-const-int-float-conversion">;
 def ImplicitIntFloatConversion : DiagGroup<"implicit-int-float-conversion",
  [ImplicitConstIntFloatConversion]>;
@@ -631,7 +633,6 @@ def Shadow : DiagGroup<"shadow", [ShadowFieldInConstructorModified,
 def ShadowAll : DiagGroup<"shadow-all", [Shadow, ShadowFieldInConstructor,
                                          ShadowUncapturedLocal, ShadowField]>;
 
-def Shorten64To32 : DiagGroup<"shorten-64-to-32">;
 def : DiagGroup<"sign-promo">;
 def SignCompare : DiagGroup<"sign-compare">;
 def SwitchDefault  : DiagGroup<"switch-default">;
@@ -942,7 +943,6 @@ def Conversion : DiagGroup<"conversion",
                             EnumConversion,
                             BitFieldEnumConversion,
                             FloatConversion,
-                            Shorten64To32,
                             IntConversion,
                             ImplicitIntConversion,
                             ImplicitFloatConversion,

clang/test/Sema/conversion-64-32.c

@@ -9,9 +9,13 @@ typedef long long long2 __attribute__((__vector_size__(16)));
 
 int4 test1(long2 a) {
   int4  v127 = a;  // no warning.
-  return v127; 
+  return v127;
 }
 
 int test2(long v) {
   return v / 2; // expected-warning {{implicit conversion loses integer precision: 'long' to 'int'}}
 }
+
+char test3(short s) {
+  return s * 2; // no warning.
+}

clang/test/Sema/conversion-implicit-int-includes-64-to-32.c

@@ -0,0 +1,21 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -Wimplicit-int-conversion -triple x86_64-apple-darwin %s
+
+int test0(long v) {
+  return v; // expected-warning {{implicit conversion loses integer precision}}
+}
+
+typedef int  int4  __attribute__ ((vector_size(16)));
+typedef long long long2 __attribute__((__vector_size__(16)));
+
+int4 test1(long2 a) {
+  int4  v127 = a;  // no warning.
+  return v127;
+}
+
+int test2(long v) {
+  return v / 2; // expected-warning {{implicit conversion loses integer precision: 'long' to 'int'}}
+}
+
+char test3(short s) {
+  return s * 2; // expected-warning {{implicit conversion loses integer precision: 'int' to 'char'}}
+}