[clang] [clang][Sema] Subclass `-Wshorten-64-to-32` under `-Wimplicit-int-conversion` (PR #80814)

[via cfe-commits]

https://github.com/whisperity created https://github.com/llvm/llvm-project/pull/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`.

Closes #69444.

`diagtool tree` diff:

```diff
   -Wconversion
     # ...
     -Wfloat-conversion
       -Wfloat-overflow-conversion
       -Wfloat-zero-conversion
-    -Wshorten-64-to-32
     -Wint-conversion
     -Wimplicit-int-conversion
+      -Wshorten-64-to-32
       -Wobjc-signed-char-bool-implicit-int-conversion
     -Wimplicit-float-conversion
       -Wimplicit-int-float-conversion
         -Wimplicit-const-int-float-conversion
       -Wobjc-signed-char-bool-implicit-float-conversion
     # ...
```

>From ab626cf86a73428fdebc9e65ddc45655070614ff Mon Sep 17 00:00:00 2001
From: Whisperity <whisperity at gmail.com>
Date: Tue, 6 Feb 2024 10:08:34 +0100
Subject: [PATCH] [clang][Sema] Subclass `-Wshorten-64-to-32` under
 `-Wimplicit-int-conversion`

---
 clang/include/clang/Basic/DiagnosticGroups.td |  6 +++---
 clang/test/Sema/conversion-64-32.c            |  6 +++++-
 ...onversion-implicit-int-includes-64-to-32.c | 21 +++++++++++++++++++
 3 files changed, 29 insertions(+), 4 deletions(-)
 create mode 100644 clang/test/Sema/conversion-implicit-int-includes-64-to-32.c

diff --git a/clang/include/clang/Basic/DiagnosticGroups.td b/clang/include/clang/Basic/DiagnosticGroups.td
index 6765721ae7002c..975eca0ad9b642 100644
--- a/clang/include/clang/Basic/DiagnosticGroups.td
+++ b/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,
diff --git a/clang/test/Sema/conversion-64-32.c b/clang/test/Sema/conversion-64-32.c
index dc417edcbc2168..c172dd109f3be2 100644
--- a/clang/test/Sema/conversion-64-32.c
+++ b/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.
+}
diff --git a/clang/test/Sema/conversion-implicit-int-includes-64-to-32.c b/clang/test/Sema/conversion-implicit-int-includes-64-to-32.c
new file mode 100644
index 00000000000000..e22ccbe821f65c
--- /dev/null
+++ b/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'}}
+}