[clang] [clang] Fix constant evaluation of strchr (PR #230869)

[Vedant Singhal via cfe-commits]

https://github.com/Ved235 updated https://github.com/llvm/llvm-project/pull/230869

>From 3ae1762f92c0dba16b54c337fe8341084858c34d Mon Sep 17 00:00:00 2001
From: Vedant <vedantsinghal07 at gmail.com>
Date: Sat, 10 Oct 2026 23:29:16 +0100
Subject: [PATCH] Fix type conversion in constant evaluation of strchr

---
 clang/lib/AST/ByteCode/InterpBuiltin.cpp      | 16 ----------------
 clang/lib/AST/ExprConstant.cpp                |  7 -------
 clang/test/AST/ByteCode/builtin-functions.cpp | 12 ++++++++----
 clang/test/SemaCXX/constexpr-string.cpp       | 12 ++++++++----
 4 files changed, 16 insertions(+), 31 deletions(-)

diff --git a/clang/lib/AST/ByteCode/InterpBuiltin.cpp b/clang/lib/AST/ByteCode/InterpBuiltin.cpp
index 4a5c691d390a71..53d543928efa3e 100644
--- a/clang/lib/AST/ByteCode/InterpBuiltin.cpp
+++ b/clang/lib/AST/ByteCode/InterpBuiltin.cpp
@@ -2378,22 +2378,6 @@ static bool interp__builtin_memchr(InterpState &S, CodePtr OpPC,
   if (!isReadable(Ptr))
     return false;
 
-  if (ID == Builtin::BIstrchr || ID == Builtin::BI__builtin_strchr) {
-    int64_t DesiredTrunc;
-    if (S.getASTContext().CharTy->isSignedIntegerType())
-      DesiredTrunc =
-          Desired.trunc(S.getASTContext().getCharWidth()).getSExtValue();
-    else
-      DesiredTrunc =
-          Desired.trunc(S.getASTContext().getCharWidth()).getZExtValue();
-    // strchr compares directly to the passed integer, and therefore
-    // always fails if given an int that is not a char.
-    if (Desired != DesiredTrunc) {
-      S.Stk.push<Pointer>();
-      return true;
-    }
-  }
-
   uint64_t DesiredVal;
   if (ID == Builtin::BIwmemchr || ID == Builtin::BI__builtin_wmemchr ||
       ID == Builtin::BIwcschr || ID == Builtin::BI__builtin_wcschr) {
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index 8551f4c9ae279a..f5b562a4eab677 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -10877,13 +10877,6 @@ bool PointerExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
     switch (BuiltinOp) {
     case Builtin::BIstrchr:
     case Builtin::BI__builtin_strchr:
-      // strchr compares directly to the passed integer, and therefore
-      // always fails if given an int that is not a char.
-      if (!APSInt::isSameValue(HandleIntToIntCast(Info, E, CharTy,
-                                                  E->getArg(1)->getType(),
-                                                  Desired),
-                               Desired))
-        return ZeroInitialization(E);
       StopAtNull = true;
       [[fallthrough]];
     case Builtin::BImemchr:
diff --git a/clang/test/AST/ByteCode/builtin-functions.cpp b/clang/test/AST/ByteCode/builtin-functions.cpp
index 211c3e98d161c4..ae07bae2779629 100644
--- a/clang/test/AST/ByteCode/builtin-functions.cpp
+++ b/clang/test/AST/ByteCode/builtin-functions.cpp
@@ -1825,11 +1825,15 @@ namespace Strchr {
   static_assert(__builtin_strchr(kStr, 'd') == nullptr);
   static_assert(__builtin_strchr(kStr, 'e') == nullptr);
   static_assert(__builtin_strchr(kStr, '\0') == kStr + 5);
-  static_assert(__builtin_strchr(kStr, 'a' + 256) == nullptr);
-  static_assert(__builtin_strchr(kStr, 'a' - 256) == nullptr);
+  static_assert(__builtin_strchr(kStr, 256) == kStr + 5);
+  static_assert(__builtin_strchr(kStr, -256) == kStr + 5);
+  static_assert(__builtin_strchr(kStr, 'a' + 256) == kStr);
+  static_assert(__builtin_strchr(kStr, 'a' - 256) == kStr);
   static_assert(__builtin_strchr(kStr, '\xff') == kStr + 4);
-  static_assert(__builtin_strchr(kStr, '\xff' + 256) == nullptr);
-  static_assert(__builtin_strchr(kStr, '\xff' - 256) == nullptr);
+  static_assert(__builtin_strchr(kStr, '\xff' + 256) == kStr + 4);
+  static_assert(__builtin_strchr(kStr, '\xff' - 256) == kStr + 4);
+  constexpr char kStr2[] = "\x80\x41";
+  static_assert(__builtin_strchr(kStr2, 128) == kStr2);
   static_assert(__builtin_strchr(kFoo, 'o') == kFoo + 1);
   static_assert(__builtin_strchr(kFoo, 'x') == nullptr); // both-error {{not an integral constant}} \
                                                          // both-note {{dereferenced one-past-the-end}}
diff --git a/clang/test/SemaCXX/constexpr-string.cpp b/clang/test/SemaCXX/constexpr-string.cpp
index b49979bbc8ca0e..b55118ffc9e2a5 100644
--- a/clang/test/SemaCXX/constexpr-string.cpp
+++ b/clang/test/SemaCXX/constexpr-string.cpp
@@ -369,11 +369,15 @@ namespace StrchrEtc {
   static_assert(__builtin_strchr(kStr, 'd') == nullptr);
   static_assert(__builtin_strchr(kStr, 'e') == nullptr);
   static_assert(__builtin_strchr(kStr, '\0') == kStr + 5);
-  static_assert(__builtin_strchr(kStr, 'a' + 256) == nullptr);
-  static_assert(__builtin_strchr(kStr, 'a' - 256) == nullptr);
+  static_assert(__builtin_strchr(kStr, 256) == kStr + 5);
+  static_assert(__builtin_strchr(kStr, -256) == kStr + 5);
+  static_assert(__builtin_strchr(kStr, 'a' + 256) == kStr);
+  static_assert(__builtin_strchr(kStr, 'a' - 256) == kStr);
   static_assert(__builtin_strchr(kStr, '\xff') == kStr + 4);
-  static_assert(__builtin_strchr(kStr, '\xff' + 256) == nullptr);
-  static_assert(__builtin_strchr(kStr, '\xff' - 256) == nullptr);
+  static_assert(__builtin_strchr(kStr, '\xff' + 256) == kStr + 4);
+  static_assert(__builtin_strchr(kStr, '\xff' - 256) == kStr + 4);
+  constexpr char kStr2[] = "\x80\x41";
+  static_assert(__builtin_strchr(kStr2, 128) == kStr2);
   static_assert(__builtin_strchr(kFoo, 'o') == kFoo + 1);
   static_assert(__builtin_strchr(kFoo, 'x') == nullptr); // expected-error {{not an integral constant}} expected-note {{dereferenced one-past-the-end}}
   static_assert(__builtin_strchr(nullptr, 'x') == nullptr); // expected-error {{not an integral constant}} expected-note {{dereferenced null}}