[clang] [clang][bytecode] Fix stack corruption in pointer arithmetic discard (PR #176555)

[via cfe-commits]

https://github.com/Serosh-commits updated https://github.com/llvm/llvm-project/pull/176555

>From c01243bcbc79068bce0a3f7ad5a3779d53ea97c1 Mon Sep 17 00:00:00 2001
From: Serosh <janmejayapanda400 at gmail.com>
Date: Sat, 17 Jan 2026 16:46:46 +0530
Subject: [PATCH] [clang][bytecode] Fix stack corruption in pointer arithmetic
 discard

In VisitPointerArithBinOp, the result of pointer addition or subtraction
was always left on the stack, even if the result was intended to be
discarded (e.g. in a comma expression). This led to stack corruption
where subsequent operations would find an unexpected pointer on the
stack, causing an assertion failure in the InterpStack.

This patch ensures that we correctly respect the DiscardResult flag
for pointer arithmetic operations.

Fixes #176549
---
 clang/lib/AST/ByteCode/Compiler.cpp  | 20 +++++++++++---------
 clang/test/AST/ByteCode/gh176549.cpp |  8 ++++++++
 2 files changed, 19 insertions(+), 9 deletions(-)
 create mode 100644 clang/test/AST/ByteCode/gh176549.cpp

diff --git a/clang/lib/AST/ByteCode/Compiler.cpp b/clang/lib/AST/ByteCode/Compiler.cpp
index 21f8db06919ed..66b0cc4b5f6ab 100644
--- a/clang/lib/AST/ByteCode/Compiler.cpp
+++ b/clang/lib/AST/ByteCode/Compiler.cpp
@@ -1083,20 +1083,22 @@ bool Compiler<Emitter>::VisitPointerArithBinOp(const BinaryOperator *E) {
   if (Op == BO_Add) {
     if (!this->emitAddOffset(OffsetType, E))
       return false;
-
-    if (classifyPrim(E) != PT_Ptr)
-      return this->emitDecayPtr(PT_Ptr, classifyPrim(E), E);
-    return true;
-  }
-  if (Op == BO_Sub) {
+  } else if (Op == BO_Sub) {
     if (!this->emitSubOffset(OffsetType, E))
       return false;
+  } else {
+    return false;
+  }
 
-    if (classifyPrim(E) != PT_Ptr)
-      return this->emitDecayPtr(PT_Ptr, classifyPrim(E), E);
-    return true;
+  if (classifyPrim(E) != PT_Ptr) {
+    if (!this->emitDecayPtr(PT_Ptr, classifyPrim(E), E))
+      return false;
   }
 
+  if (DiscardResult)
+    return this->emitPop(classifyPrim(E), E);
+  return true;
+
   return false;
 }
 
diff --git a/clang/test/AST/ByteCode/gh176549.cpp b/clang/test/AST/ByteCode/gh176549.cpp
new file mode 100644
index 0000000000000..b56f762b7ede4
--- /dev/null
+++ b/clang/test/AST/ByteCode/gh176549.cpp
@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -fexperimental-new-constant-interpreter -verify %s
+// expected-no-diagnostics
+
+const char a[4] = "abc";
+void foo() {
+  int i = 0;
+  i = 1 > (a + 1, sizeof(a));
+}