[clang][Interp] Implement __builtin_clrsb (#72243)

Author: tbaederr

clang/lib/AST/Interp/InterpBuiltin.cpp

@@ -448,6 +448,15 @@ static bool interp__builtin_parity(InterpState &S, CodePtr OpPC,
   return true;
 }
 
+static bool interp__builtin_clrsb(InterpState &S, CodePtr OpPC,
+                                  const InterpFrame *Frame,
+                                  const Function *Func, const CallExpr *Call) {
+  PrimType ArgT = *S.getContext().classify(Call->getArg(0)->getType());
+  APSInt Val = peekToAPSInt(S.Stk, ArgT);
+  pushInt(S, Val.getBitWidth() - Val.getSignificantBits());
+  return true;
+}
+
 bool InterpretBuiltin(InterpState &S, CodePtr OpPC, const Function *F,
                       const CallExpr *Call) {
   InterpFrame *Frame = S.Current;
@@ -592,6 +601,13 @@ bool InterpretBuiltin(InterpState &S, CodePtr OpPC, const Function *F,
       return retInt(S, OpPC, Dummy);
     break;
 
+  case Builtin::BI__builtin_clrsb:
+  case Builtin::BI__builtin_clrsbl:
+  case Builtin::BI__builtin_clrsbll:
+    if (interp__builtin_clrsb(S, OpPC, Frame, F, Call))
+      return retInt(S, OpPC, Dummy);
+    break;
+
   default:
     return false;
   }

clang/test/AST/Interp/builtin-functions.cpp

@@ -310,3 +310,17 @@ namespace parity {
   char parity10[__builtin_parityll(1LL << (BITSIZE(long long) - 1)) == 1 ? 1 : -1];
 }
 
+namespace clrsb {
+  char clrsb1[__builtin_clrsb(0) == BITSIZE(int) - 1 ? 1 : -1];
+  char clrsb2[__builtin_clrsbl(0L) == BITSIZE(long) - 1 ? 1 : -1];
+  char clrsb3[__builtin_clrsbll(0LL) == BITSIZE(long long) - 1 ? 1 : -1];
+  char clrsb4[__builtin_clrsb(~0) == BITSIZE(int) - 1 ? 1 : -1];
+  char clrsb5[__builtin_clrsbl(~0L) == BITSIZE(long) - 1 ? 1 : -1];
+  char clrsb6[__builtin_clrsbll(~0LL) == BITSIZE(long long) - 1 ? 1 : -1];
+  char clrsb7[__builtin_clrsb(1) == BITSIZE(int) - 2 ? 1 : -1];
+  char clrsb8[__builtin_clrsb(~1) == BITSIZE(int) - 2 ? 1 : -1];
+  char clrsb9[__builtin_clrsb(1 << (BITSIZE(int) - 1)) == 0 ? 1 : -1];
+  char clrsb10[__builtin_clrsb(~(1 << (BITSIZE(int) - 1))) == 0 ? 1 : -1];
+  char clrsb11[__builtin_clrsb(0xf) == BITSIZE(int) - 5 ? 1 : -1];
+  char clrsb12[__builtin_clrsb(~0x1f) == BITSIZE(int) - 6 ? 1 : -1];
+}