[clang] [CIR] Implement 'bzero' builtin lowering in terms of cir.libc.memcpy (PR #184835)

[Andy Kaylor via cfe-commits]

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@@ -1575,8 +1575,20 @@ RValue CIRGenFunction::emitBuiltinExpr(const GlobalDecl &gd, unsigned builtinID,
   case Builtin::BI__builtin_alloca_with_align_uninitialized:
   case Builtin::BI__builtin_alloca_with_align:
   case Builtin::BI__builtin_infer_alloc_token:
+    return errorBuiltinNYI(*this, e, builtinID);
   case Builtin::BIbzero:
-  case Builtin::BI__builtin_bzero:
+  case Builtin::BI__builtin_bzero: {
+    mlir::Location loc = getLoc(e->getSourceRange());
+    Address destPtr = emitPointerWithAlignment(e->getArg(0));
+    mlir::Value destPtrCast =
+        builder.createPtrBitcast(destPtr.getPointer(), cgm.voidTy);
+    mlir::Value size = emitScalarExpr(e->getArg(1));
+    mlir::Value zero = builder.getNullValue(builder.getUInt8Ty(), loc);
+    assert(!cir::MissingFeatures::sanitizers());
+    builder.createMemSet(loc, destPtrCast, zero, size);
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andykaylor wrote:

Do we need alignment here? We're calling `emitPointerWithAlignment` to get an Address, but then by switching to mlir::Value, we're not passing that alignment on to the memset. The bitcast on line 1584 could be replaced by `destPtrCast = destPtr.withElementType(builder, cgm.voidTy);` to keep it as an address (`withElementType` inserts a bitcast), but we'd need a version of `createMemSet` that takes an Address and does something with the alignment.

https://github.com/llvm/llvm-project/pull/184835