[clang] 9e47955 - [clang][bytecode] Move builtin-id check to compilation phase (#227646)

[via cfe-commits]

Author: Timm Baeder
Date: 2026-09-30T14:14:54+02:00
New Revision: 9e47955ee962499879f570800a97bb58629be5f9

URL: https://github.com/llvm/llvm-project/commit/9e47955ee962499879f570800a97bb58629be5f9
DIFF: https://github.com/llvm/llvm-project/commit/9e47955ee962499879f570800a97bb58629be5f9.diff

LOG: [clang][bytecode] Move builtin-id check to compilation phase (#227646)

First, a builtin won't magically become constexpr between two
compilations of the same builtin id, so we're re-doing the check over
and over again for every call of a builtin function, which is
unnecessary.

Second, in the case where the builtin _isn't_ constexpr, there was a
diagnostic discrepancy between the two evaluators. We now correctly
reject the builtin call before even trying to evaluate its arguments.

Added: 
    

Modified: 
    clang/lib/AST/ByteCode/Compiler.cpp
    clang/lib/AST/ByteCode/InterpBuiltin.cpp
    clang/test/AST/ByteCode/builtin-functions.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/AST/ByteCode/Compiler.cpp b/clang/lib/AST/ByteCode/Compiler.cpp
index dcc00c0e14945..313687f538169 100644
--- a/clang/lib/AST/ByteCode/Compiler.cpp
+++ b/clang/lib/AST/ByteCode/Compiler.cpp
@@ -6167,6 +6167,21 @@ bool Compiler<Emitter>::registerRedecl(const VarDecl *VD, const APValue &Val) {
 template <class Emitter>
 bool Compiler<Emitter>::VisitBuiltinCallExpr(const CallExpr *E,
                                              unsigned BuiltinID) {
+  const ASTContext &ASTCtx = Ctx.getASTContext();
+
+  // BuiltinID is the raw ID baked into the bytecode. The "is constant
+  // evaluated" gate needs the raw ID so that auxiliary-target IDs resolve into
+  // the correct (aux-target) builtin records.
+  if (!Ctx.getASTContext().BuiltinInfo.isConstantEvaluated(BuiltinID))
+    return this->emitInvalid(E);
+
+  // Convert an auxiliary x86 target builtin ID to its canonical X86::BI* value
+  // so the target-specific cases below (and the handlers they call) match. This
+  // is a cheap integer operation (a single comparison for the common,
+  // target-independent case); we deliberately avoid re-deriving the ID from the
+  // call expression, which is comparatively slow.
+  BuiltinID = ConvertBuiltinIDToX86BuiltinID(ASTCtx, BuiltinID);
+
   if (BuiltinID == Builtin::BI__builtin_constant_p) {
     // Void argument is always invalid and harder to handle later.
     if (E->getArg(0)->getType()->isVoidType()) {

diff  --git a/clang/lib/AST/ByteCode/InterpBuiltin.cpp b/clang/lib/AST/ByteCode/InterpBuiltin.cpp
index 843850af334a2..3303a56f2c053 100644
--- a/clang/lib/AST/ByteCode/InterpBuiltin.cpp
+++ b/clang/lib/AST/ByteCode/InterpBuiltin.cpp
@@ -4600,21 +4600,6 @@ static bool interp_builtin_ia32_cvt_vector_to_int(InterpState &S, CodePtr OpPC,
 
 bool InterpretBuiltin(InterpState &S, CodePtr OpPC, const CallExpr *Call,
                       uint32_t BuiltinID) {
-  const ASTContext &ASTCtx = S.getASTContext();
-
-  // BuiltinID is the raw ID baked into the bytecode. The "is constant
-  // evaluated" gate needs the raw ID so that auxiliary-target IDs resolve into
-  // the correct (aux-target) builtin records.
-  if (!ASTCtx.BuiltinInfo.isConstantEvaluated(BuiltinID))
-    return Invalid(S, OpPC);
-
-  // Convert an auxiliary x86 target builtin ID to its canonical X86::BI* value
-  // so the target-specific cases below (and the handlers they call) match. This
-  // is a cheap integer operation (a single comparison for the common,
-  // target-independent case); we deliberately avoid re-deriving the ID from the
-  // call expression, which is comparatively slow.
-  BuiltinID = ConvertBuiltinIDToX86BuiltinID(ASTCtx, BuiltinID);
-
   const InterpFrame *Frame = S.Current;
   switch (BuiltinID) {
   case Builtin::BI__builtin_is_constant_evaluated:
@@ -6723,11 +6708,7 @@ bool InterpretBuiltin(InterpState &S, CodePtr OpPC, const CallExpr *Call,
   case X86::BI__builtin_ia32_cvttps2dq256:
     return interp_builtin_ia32_cvt_vector_to_int(S, OpPC, Call);
   default:
-    S.FFDiag(S.Current->getLocation(OpPC),
-             diag::note_invalid_subexpr_in_const_expr)
-        << S.Current->getRange(OpPC);
-
-    return false;
+    return Invalid(S, OpPC);
   }
 
   llvm_unreachable("Unhandled builtin ID");

diff  --git a/clang/test/AST/ByteCode/builtin-functions.cpp b/clang/test/AST/ByteCode/builtin-functions.cpp
index 5d8c0fa2b7b6b..211c3e98d161c 100644
--- a/clang/test/AST/ByteCode/builtin-functions.cpp
+++ b/clang/test/AST/ByteCode/builtin-functions.cpp
@@ -2153,3 +2153,13 @@ namespace ReduceMin {
   typedef float v4f __attribute__((__vector_size__(16)));
   static_assert(__builtin_reduce_min((v4f){1.123, 2.123, 3.123, 4.123}) == 0); // both-error {{not an integral constant expression}}
 }
+
+namespace Rejected {
+  constexpr int foo() { // both-error {{never produces a constant expression}}
+    __builtin_alloca(10 / 0); // both-note 2{{subexpression not valid in a constant expression}} \
+                              // both-warning {{division by zero is undefined}}
+    return 1;
+  }
+  static_assert(foo() == 1); // both-error {{not an integral constant expression}} \
+                             // both-note {{in call to}}
+}