commit 612a105c46a77dc4c1c04d1e5cdd85d1b77decec
author Simon Pilgrim <llvm-dev@redking.me.uk> Tue Sep 23 14:14:41 2025 +0100
committer GitHub <noreply@github.com> Tue Sep 23 13:14:41 2025 +0000
tree d6f843c8361ad14b0d782ac2c4ca0596d3ec07e5
parent 004e462682231548c9cf054be2341d3f5087ebbe

[clang][byte] Add callback mechanism to handle constexpr for unary integer ops (#160280)

Add interp__builtin_elementwise_int_unaryop - similar to what we already have with interp__builtin_elementwise_int_binop to handle binops

Update x86 lzcnt/tzcnt intrinsics to use with a suitable callback

I'll add vector handling in a future patch when we add x86 vector intrinsics that can use it

clang/lib/AST/ByteCode/InterpBuiltin.cpp

diff --git a/clang/lib/AST/ByteCode/InterpBuiltin.cpp b/clang/lib/AST/ByteCode/InterpBuiltin.cpp
index 4b259da..aaab8ad 100644
--- a/clang/lib/AST/ByteCode/InterpBuiltin.cpp
+++ b/clang/lib/AST/ByteCode/InterpBuiltin.cpp
@@ -1380,32 +1380,6 @@
   return true;
 }
 
-static bool interp__builtin_ia32_lzcnt(InterpState &S, CodePtr OpPC,
-                                       const InterpFrame *Frame,
-                                       const CallExpr *Call) {
-  QualType CallType = Call->getType();
-  if (!CallType->isIntegerType() ||
-      !Call->getArg(0)->getType()->isIntegerType())
-    return false;
-
-  APSInt Val = popToAPSInt(S, Call->getArg(0));
-  pushInteger(S, Val.countLeadingZeros(), CallType);
-  return true;
-}
-
-static bool interp__builtin_ia32_tzcnt(InterpState &S, CodePtr OpPC,
-                                       const InterpFrame *Frame,
-                                       const CallExpr *Call) {
-  QualType CallType = Call->getType();
-  if (!CallType->isIntegerType() ||
-      !Call->getArg(0)->getType()->isIntegerType())
-    return false;
-
-  APSInt Val = popToAPSInt(S, Call->getArg(0));
-  pushInteger(S, Val.countTrailingZeros(), CallType);
-  return true;
-}
-
 static bool interp__builtin_ia32_pdep(InterpState &S, CodePtr OpPC,
                                       const InterpFrame *Frame,
                                       const CallExpr *Call) {
@@ -2551,6 +2525,24 @@
   return true;
 }
 
+static bool interp__builtin_elementwise_int_unaryop(
+    InterpState &S, CodePtr OpPC, const CallExpr *Call,
+    llvm::function_ref<APInt(const APSInt &)> Fn) {
+  assert(Call->getNumArgs() == 1);
+  assert(Call->getType()->isIntegerType());
+
+  // Single integer case.
+  if (!Call->getArg(0)->getType()->isVectorType()) {
+    APSInt Src = popToAPSInt(S, Call->getArg(0));
+    APInt Result = Fn(Src);
+    pushInteger(S, APSInt(std::move(Result), !Src.isSigned()), Call->getType());
+    return true;
+  }
+
+  // TODO: Add vector integer handling.
+  return false;
+}
+
 static bool interp__builtin_elementwise_int_binop(
     InterpState &S, CodePtr OpPC, const CallExpr *Call,
     llvm::function_ref<APInt(const APSInt &, const APSInt &)> Fn) {
@@ -3283,12 +3275,18 @@
   case clang::X86::BI__builtin_ia32_lzcnt_u16:
   case clang::X86::BI__builtin_ia32_lzcnt_u32:
   case clang::X86::BI__builtin_ia32_lzcnt_u64:
-    return interp__builtin_ia32_lzcnt(S, OpPC, Frame, Call);
+    return interp__builtin_elementwise_int_unaryop(
+        S, OpPC, Call, [](const APSInt &Src) {
+          return APInt(Src.getBitWidth(), Src.countLeadingZeros());
+        });
 
   case clang::X86::BI__builtin_ia32_tzcnt_u16:
   case clang::X86::BI__builtin_ia32_tzcnt_u32:
   case clang::X86::BI__builtin_ia32_tzcnt_u64:
-    return interp__builtin_ia32_tzcnt(S, OpPC, Frame, Call);
+    return interp__builtin_elementwise_int_unaryop(
+        S, OpPC, Call, [](const APSInt &Src) {
+          return APInt(Src.getBitWidth(), Src.countTrailingZeros());
+        });
 
   case clang::X86::BI__builtin_ia32_pdep_si:
   case clang::X86::BI__builtin_ia32_pdep_di: