[Sema] Re-land: Diagnose tautological comparison with type's min/max values

The first attempt, rL315614 was reverted because one libcxx
test broke, and i did not know at the time how to deal with it.

Summary:
Currently, clang only diagnoses completely out-of-range comparisons (e.g. `char` and constant `300`),
and comparisons of unsigned and `0`. But gcc also does diagnose the comparisons with the
`std::numeric_limits<>::max()` / `std::numeric_limits<>::min()` so to speak

Finally Fixes https://bugs.llvm.org/show_bug.cgi?id=34147
Continuation of https://reviews.llvm.org/D37565

Reviewers: rjmccall, rsmith, aaron.ballman

Reviewed By: rsmith

Subscribers: rtrieu, jroelofs, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D38101

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@315875 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 5 insertions, 3 deletions

diff --git a/include/clang/Basic/DiagnosticGroups.td b/include/clang/Basic/DiagnosticGroups.td
index ae6f51775e..2f4244c98e 100644
--- a/include/clang/Basic/DiagnosticGroups.td
+++ b/include/clang/Basic/DiagnosticGroups.td
@@ -432,13 +432,15 @@ def StrncatSize : DiagGroup<"strncat-size">;
 def TautologicalUnsignedZeroCompare : DiagGroup<"tautological-unsigned-zero-compare">;
 def TautologicalUnsignedEnumZeroCompare : DiagGroup<"tautological-unsigned-enum-zero-compare">;
 def TautologicalOutOfRangeCompare : DiagGroup<"tautological-constant-out-of-range-compare">;
+def TautologicalConstantCompare : DiagGroup<"tautological-constant-compare",
+                                            [TautologicalUnsignedZeroCompare,
+                                             TautologicalUnsignedEnumZeroCompare,
+                                             TautologicalOutOfRangeCompare]>;
 def TautologicalPointerCompare : DiagGroup<"tautological-pointer-compare">;
 def TautologicalOverlapCompare : DiagGroup<"tautological-overlap-compare">;
 def TautologicalUndefinedCompare : DiagGroup<"tautological-undefined-compare">;
 def TautologicalCompare : DiagGroup<"tautological-compare",
-                                    [TautologicalUnsignedZeroCompare,
-                                     TautologicalUnsignedEnumZeroCompare,
-                                     TautologicalOutOfRangeCompare,
+                                    [TautologicalConstantCompare,
                                      TautologicalPointerCompare,
                                      TautologicalOverlapCompare,
                                      TautologicalUndefinedCompare]>;