[clang] [clang][Sema] Warn consecutive builtin comparisons in an expression (PR #92200)

[Youngsuk Kim via cfe-commits]

https://github.com/JOE1994 updated https://github.com/llvm/llvm-project/pull/92200

>From 2c7f9a083c129df70a79d019286b6a29643a8973 Mon Sep 17 00:00:00 2001
From: Youngsuk Kim <youngsuk.kim at hpe.com>
Date: Tue, 14 May 2024 17:42:59 -0500
Subject: [PATCH 1/2] [clang][Sema] Warn consecutive builtin comparisons in an
 expression

Made the following decisions for consistency with `gcc 14.1`:
* Add warning under -Wparentheses
* Set the warning to DefaultIgnore, although -Wparentheses is enabled by default
  * This warning is only issued when -Wparentheses is explicitly enabled
    (via -Wparentheses or -Wall)

Closes #20456
---
 clang/docs/ReleaseNotes.rst                      | 3 +++
 clang/include/clang/Basic/DiagnosticSemaKinds.td | 4 ++++
 clang/lib/Sema/SemaExpr.cpp                      | 5 +++++
 clang/test/Sema/parentheses.cpp                  | 7 +++++++
 4 files changed, 19 insertions(+)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index ae699ebfc6038..13d58e69aeeb7 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -487,6 +487,9 @@ Improvements to Clang's diagnostics
        }
      };
 
+- Clang emits a ``-Wparentheses`` warning for expressions with consecutive comparisons like ``x < y < z``.
+  It was made a ``-Wparentheses`` warning to be consistent with gcc.
+
 Improvements to Clang's time-trace
 ----------------------------------
 
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 6100fba510059..612043f410890 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -6911,6 +6911,10 @@ def warn_precedence_bitwise_conditional : Warning<
 def note_precedence_conditional_first : Note<
   "place parentheses around the '?:' expression to evaluate it first">;
 
+def warn_consecutive_comparison : Warning<
+  "comparisons like 'X<=Y<=Z' don't have their mathematical meaning">,
+  InGroup<Parentheses>, DefaultIgnore;
+
 def warn_enum_constant_in_bool_context : Warning<
   "converting the enum constant to a boolean">,
   InGroup<IntInBoolContext>, DefaultIgnore;
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index ec84798e4ce60..fab34f4fa3e14 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -14878,6 +14878,11 @@ ExprResult Sema::CreateBuiltinBinOp(SourceLocation OpLoc,
   case BO_GT:
     ConvertHalfVec = true;
     ResultTy = CheckCompareOperands(LHS, RHS, OpLoc, Opc);
+
+    if (const auto *BI = dyn_cast<BinaryOperator>(LHSExpr))
+      if (BI->isComparisonOp())
+        Diag(OpLoc, diag::warn_consecutive_comparison);
+
     break;
   case BO_EQ:
   case BO_NE:
diff --git a/clang/test/Sema/parentheses.cpp b/clang/test/Sema/parentheses.cpp
index 324d9b5f1e414..8e546461fb643 100644
--- a/clang/test/Sema/parentheses.cpp
+++ b/clang/test/Sema/parentheses.cpp
@@ -215,3 +215,10 @@ namespace PR20735 {
     // fix-it:"{{.*}}":{[[@LINE-9]]:20-[[@LINE-9]]:20}:")"
   }
 }
+
+void consecutive_builtin_compare(int x, int y, int z) {
+  (void)(x < y < z);  // expected-warning {{comparisons like 'X<=Y<=Z' don't have their mathematical meaning}}
+  (void)(x < y > z);  // expected-warning {{comparisons like 'X<=Y<=Z' don't have their mathematical meaning}}
+  (void)(x < y <= z); // expected-warning {{comparisons like 'X<=Y<=Z' don't have their mathematical meaning}}
+  (void)(x <= y > z); // expected-warning {{comparisons like 'X<=Y<=Z' don't have their mathematical meaning}}
+}

>From b3cc457efc40a345d4b67c776edd470e35f73de2 Mon Sep 17 00:00:00 2001
From: Youngsuk Kim <joseph942010 at gmail.com>
Date: Wed, 15 May 2024 13:20:06 -0400
Subject: [PATCH 2/2] Update clang/lib/Sema/SemaExpr.cpp

Co-authored-by: Aaron Ballman <aaron at aaronballman.com>
---
 clang/lib/Sema/SemaExpr.cpp | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index fab34f4fa3e14..b4c54a3da42c0 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -14879,9 +14879,8 @@ ExprResult Sema::CreateBuiltinBinOp(SourceLocation OpLoc,
     ConvertHalfVec = true;
     ResultTy = CheckCompareOperands(LHS, RHS, OpLoc, Opc);
 
-    if (const auto *BI = dyn_cast<BinaryOperator>(LHSExpr))
-      if (BI->isComparisonOp())
-        Diag(OpLoc, diag::warn_consecutive_comparison);
+    if (const auto *BI = dyn_cast<BinaryOperator>(LHSExpr); BI && BI->isComparisonOp())
+      Diag(OpLoc, diag::warn_consecutive_comparison);
 
     break;
   case BO_EQ: