[clang] [clang][Sema] Re-use existing BinaryOperator if possible (PR #90625)

[Youngsuk Kim via cfe-commits]

https://github.com/JOE1994 created https://github.com/llvm/llvm-project/pull/90625

First round of Sema checks were run at initial parsing step. Creating a new BinaryOperator instance (with the re-built LHS or RHS) will trigger another round of Sema checks, which can lead to duplicate diagnostic warning messages.

All we want here is to replace the LHS or RHS with a NonOdrUse version. Don't create a new BinaryOperator, but simply replace the LHS or RHS of the given BinaryOperator.

Fixes #45783

>From 24eb4db70e296d6454bac4c84a5bbc47e638876f Mon Sep 17 00:00:00 2001
From: Youngsuk Kim <youngsuk.kim at hpe.com>
Date: Tue, 30 Apr 2024 11:18:15 -0500
Subject: [PATCH] [clang][Sema] Re-use existing BinaryOperator if possible

First round of Sema checks were run at initial parsing step. Creating a new
BinaryOperator instance (with the re-built LHS or RHS) will trigger another
round of Sema checks, which can lead to duplicate diagnostic warning messages.

All we want here is to replace the LHS or RHS with a NonOdrUse version. Don't
create a new BinaryOperator, but simply replace the LHS or RHS of the given
BinaryOperator.

Fixes #45783
---
 clang/lib/Sema/SemaExpr.cpp  | 7 +++----
 clang/test/CXX/drs/dr7xx.cpp | 2 --
 2 files changed, 3 insertions(+), 6 deletions(-)

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 50f92c496a539a..27733cd857d964 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -19707,18 +19707,17 @@ static ExprResult rebuildPotentialResultsAsNonOdrUsed(Sema &S, Expr *E,
       ExprResult Sub = Rebuild(LHS);
       if (!Sub.isUsable())
         return Sub;
-      LHS = Sub.get();
+      BO->setLHS(Sub.get());
     //   -- If e is a comma expression, ...
     } else if (BO->getOpcode() == BO_Comma) {
       ExprResult Sub = Rebuild(RHS);
       if (!Sub.isUsable())
         return Sub;
-      RHS = Sub.get();
+      BO->setRHS(Sub.get());
     } else {
       break;
     }
-    return S.BuildBinOp(nullptr, BO->getOperatorLoc(), BO->getOpcode(),
-                        LHS, RHS);
+    return ExprResult(BO);
   }
 
   //   -- If e has the form (e1)...
diff --git a/clang/test/CXX/drs/dr7xx.cpp b/clang/test/CXX/drs/dr7xx.cpp
index 69ee6d6d4e6ae0..0300dae08d6d31 100644
--- a/clang/test/CXX/drs/dr7xx.cpp
+++ b/clang/test/CXX/drs/dr7xx.cpp
@@ -28,10 +28,8 @@ namespace cwg712 { // cwg712: partial
         use(a);
         use((a));
         use(cond ? a : a);
-        // FIXME: should only warn once
         use((cond, a));
         // expected-warning at -1 {{left operand of comma operator has no effect}}
-        // expected-warning at -2 {{left operand of comma operator has no effect}}
 
         (void)a;
         // expected-error at -1 {{reference to local variable 'a' declared in enclosing function 'cwg712::f'}} FIXME