llvmjit: Also copy parameter / return value attributes from template functions.

Previously we only copied the function attributes. That caused problems at
least on s390x: Because we didn't copy the 'zeroext' attribute for
ExecAggTransReparent()'s *IsNull parameters, expressions invoking it didn't
ensure that the upper bytes of the registers were zeroed. In the - relatively
rare - cases where not, ExecAggTransReparent() wrongly ended up in the
newValueIsNull branch due to the register not being zero. Subsequently causing
a crash.

It's quite possible that this would cause problems on other platforms, and in
other places than just ExecAggTransReparent() on s390x.

Thanks to Christoph (and the Debian project) for providing me with access to a
s390x machine, allowing me to debug this.

Reported-By: Christoph Berg
Author: Andres Freund
Discussion: https://postgr.es/m/20201015083246.kie5726xerdt3ael@alap3.anarazel.de
Backpatch: 11-, where JIT was added

src/backend/jit/llvm/llvmjit.c

@@ -324,26 +324,46 @@ llvm_pg_func(LLVMModuleRef mod, const char *funcname)
 }
 
 /*
- * Copy attributes from one function to another.
+ * Copy attributes from one function to another, for a specific index (an
+ * index can reference return value, function and parameter attributes).
  */
-void
-llvm_copy_attributes(LLVMValueRef v_from, LLVMValueRef v_to)
+static void
+llvm_copy_attributes_at_index(LLVMValueRef v_from, LLVMValueRef v_to, uint32 index)
 {
 	int			num_attributes;
-	int			attno;
 	LLVMAttributeRef *attrs;
 
-	num_attributes =
-		LLVMGetAttributeCountAtIndex(v_from, LLVMAttributeFunctionIndex);
+	num_attributes = LLVMGetAttributeCountAtIndex(v_from, index);
 
 	attrs = palloc(sizeof(LLVMAttributeRef) * num_attributes);
-	LLVMGetAttributesAtIndex(v_from, LLVMAttributeFunctionIndex, attrs);
+	LLVMGetAttributesAtIndex(v_from, index, attrs);
 
-	for (attno = 0; attno < num_attributes; attno++)
-	{
-		LLVMAddAttributeAtIndex(v_to, LLVMAttributeFunctionIndex,
-								attrs[attno]);
-	}
+	for (int attno = 0; attno < num_attributes; attno++)
+		LLVMAddAttributeAtIndex(v_to, index, attrs[attno]);
+
+	pfree(attrs);
+}
+
+/*
+ * Copy all attributes from one function to another. I.e. function, return and
+ * parameters will be copied.
+ */
+void
+llvm_copy_attributes(LLVMValueRef v_from, LLVMValueRef v_to)
+{
+	uint32		param_count;
+
+	/* copy function attributes */
+	llvm_copy_attributes_at_index(v_from, v_to, LLVMAttributeFunctionIndex);
+
+	/* and the return value attributes */
+	llvm_copy_attributes_at_index(v_from, v_to, LLVMAttributeReturnIndex);
+
+	/* and each function parameter's attribute */
+	param_count = LLVMCountParams(v_from);
+
+	for (int paramidx = 1; paramidx <= param_count; paramidx++)
+		llvm_copy_attributes_at_index(v_from, v_to, paramidx);
 }
 
 /*