[clang] [Clang] Add __builtin_bswapg (PR #162433)

[via cfe-commits]

https://github.com/clingfei updated https://github.com/llvm/llvm-project/pull/162433

>From d78fb8398d4da4bc975c1315583f944d0e082281 Mon Sep 17 00:00:00 2001
From: clingfei <1599101385 at qq.com>
Date: Wed, 8 Oct 2025 15:05:44 +0800
Subject: [PATCH] [Clang] Add __builtin_bswapg

---
 clang/include/clang/Basic/Builtins.td |  6 ++++++
 clang/lib/AST/ExprConstant.cpp        | 11 +++++++++++
 clang/lib/Sema/SemaChecking.cpp       | 28 +++++++++++++++++++++++++++
 3 files changed, 45 insertions(+)

diff --git a/clang/include/clang/Basic/Builtins.td b/clang/include/clang/Basic/Builtins.td
index 468121f7d20ab..e65ed2f20be97 100644
--- a/clang/include/clang/Basic/Builtins.td
+++ b/clang/include/clang/Basic/Builtins.td
@@ -755,6 +755,12 @@ def BSwap : Builtin, Template<["unsigned short", "uint32_t", "uint64_t"],
   let Prototype = "T(T)";
 }
 
+def BSwapg : Builtin {
+  let Spellings = ["__builtin_bswapg"];
+  let Attributes = [NoThrow, Const, Constexpr, CustomTypeChecking];
+  let Prototype = "int(...)";
+}
+
 def Bitreverse : BitInt8_16_32_64BuiltinsTemplate, Builtin {
   let Spellings = ["__builtin_bitreverse"];
   let Attributes = [NoThrow, Const, Constexpr];
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index 618e1636e9e53..058905e7fd3c0 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -13982,6 +13982,17 @@ bool IntExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
 
     return Success(Val.reverseBits(), E);
   }
+  case Builtin::BI__builtin_bswapg: {
+    APSInt Val;
+    if (!EvaluateInteger(E->getArg(0), Val, Info))
+      return false;
+    if (Val.getBitWidth() == 8) {
+        bool ret =  Success(Val, E);
+        return ret;
+    }
+        
+    return Success(Val.byteSwap(), E);
+  }
 
   case Builtin::BI__builtin_bswap16:
   case Builtin::BI__builtin_bswap32:
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 063db05665af1..362b53676feaa 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -2200,6 +2200,30 @@ static bool BuiltinCpu(Sema &S, const TargetInfo &TI, CallExpr *TheCall,
   return false;
 }
 
+/// Checks that __builtin_bswapg was called with a single argument, which is an
+/// unsigned integer, and overrides the return value type to the integer type.
+static bool BuiltinBswapg(Sema &S, CallExpr *TheCall) {
+  if (S.checkArgCount(TheCall, 1))
+    return true;
+  ExprResult ArgRes = S.DefaultLvalueConversion(TheCall->getArg(0));
+  if (ArgRes.isInvalid())
+    return true;
+
+  Expr *Arg = ArgRes.get();
+  TheCall->setArg(0, Arg);
+
+  QualType ArgTy = Arg->getType();
+
+  if (!ArgTy->isIntegerType()) {
+    S.Diag(Arg->getBeginLoc(), diag::err_builtin_invalid_arg_type)
+        << 1 << /* scalar */ 1 << /* unsigned integer ty */ 1 << /* no fp */ 0
+        << ArgTy;
+    return true;
+  }
+  TheCall->setType(ArgTy);
+  return false;
+}
+
 /// Checks that __builtin_popcountg was called with a single argument, which is
 /// an unsigned integer.
 static bool BuiltinPopcountg(Sema &S, CallExpr *TheCall) {
@@ -3448,6 +3472,10 @@ Sema::CheckBuiltinFunctionCall(FunctionDecl *FDecl, unsigned BuiltinID,
     }
     break;
   }
+  case Builtin::BI__builtin_bswapg:
+    if (BuiltinBswapg(*this, TheCall))
+        return ExprError();
+    break;
   case Builtin::BI__builtin_popcountg:
     if (BuiltinPopcountg(*this, TheCall))
       return ExprError();