[clang] [clang][Interp] Implement __builtin_popcount() (PR #67929)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr created https://github.com/llvm/llvm-project/pull/67929

None

>From ce44117306858aa1bff3766dc640201ffd99a89f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Sun, 1 Oct 2023 19:41:15 +0200
Subject: [PATCH] [clang][Interp] Implement __builtin_popcount()

---
 clang/lib/AST/Interp/InterpBuiltin.cpp      | 20 ++++++++++++++++++++
 clang/test/AST/Interp/builtin-functions.cpp |  9 +++++++++
 2 files changed, 29 insertions(+)

diff --git a/clang/lib/AST/Interp/InterpBuiltin.cpp b/clang/lib/AST/Interp/InterpBuiltin.cpp
index d816145598049b0..bba0255219bc0d7 100644
--- a/clang/lib/AST/Interp/InterpBuiltin.cpp
+++ b/clang/lib/AST/Interp/InterpBuiltin.cpp
@@ -398,6 +398,16 @@ static bool interp__builtin_fabs(InterpState &S, CodePtr OpPC,
   return true;
 }
 
+static bool interp__builtin_popcount(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.popcount());
+  return true;
+}
+
 bool InterpretBuiltin(InterpState &S, CodePtr OpPC, const Function *F,
                       const CallExpr *Call) {
   InterpFrame *Frame = S.Current;
@@ -513,6 +523,16 @@ bool InterpretBuiltin(InterpState &S, CodePtr OpPC, const Function *F,
       return Ret<PT_Float>(S, OpPC, Dummy);
     break;
 
+  case Builtin::BI__builtin_popcount:
+  case Builtin::BI__builtin_popcountl:
+  case Builtin::BI__builtin_popcountll:
+  case Builtin::BI__popcnt16: // Microsoft variants of popcount
+  case Builtin::BI__popcnt:
+  case Builtin::BI__popcnt64:
+    if (interp__builtin_popcount(S, OpPC, Frame, F, Call))
+      return retInt(S, OpPC, Dummy);
+    break;
+
   default:
     return false;
   }
diff --git a/clang/test/AST/Interp/builtin-functions.cpp b/clang/test/AST/Interp/builtin-functions.cpp
index cd4ad010af12220..755f2b755412ef6 100644
--- a/clang/test/AST/Interp/builtin-functions.cpp
+++ b/clang/test/AST/Interp/builtin-functions.cpp
@@ -260,3 +260,12 @@ namespace SourceLocation {
     static_assert(c.a.n == __LINE__ - 1, "");
   }
 }
+
+namespace popcount {
+  static_assert(__builtin_popcount(~0u) == __CHAR_BIT__ * sizeof(unsigned int), "");
+  static_assert(__builtin_popcount(0) == 0, "");
+  static_assert(__builtin_popcountl(~0ul) == __CHAR_BIT__ * sizeof(unsigned long), "");
+  static_assert(__builtin_popcountl(0) == 0, "");
+  static_assert(__builtin_popcountll(~0ull) == __CHAR_BIT__ * sizeof(unsigned long long), "");
+  static_assert(__builtin_popcountll(0) == 0, "");
+}