jit: Support opaque pointers in LLVM 16.

Remove use of LLVMGetElementType() and provide the type of all pointers
to LLVMBuildXXX() functions when emitting IR, as required by modern LLVM
versions[1].

 * For LLVM <= 14, we'll still use the old LLVMBuildXXX() functions.
 * For LLVM == 15, we'll continue to do the same, explicitly opting
   out of opaque pointer mode.
 * For LLVM >= 16, we'll use the new LLVMBuildXXX2() functions that take
   the extra type argument.

The difference is hidden behind some new IR emitting wrapper functions
l_load(), l_gep(), l_call() etc.  The change is mostly mechanical,
except that at each site the correct type had to be provided.

In some places we needed to do some extra work to get functions types,
including some new wrappers for C++ APIs that are not yet exposed by in
LLVM's C API, and some new "example" functions in llvmjit_types.c
because it's no longer possible to start from the function pointer type
and ask for the function type.

Back-patch to 12, because it's a little tricker in 11 and we agreed not
to put the latest LLVM support into the upcoming final release of 11.

[1] https://llvm.org/docs/OpaquePointers.html

Reviewed-by: Dmitry Dolgov <9erthalion6@gmail.com>
Reviewed-by: Ronan Dunklau <ronan.dunklau@aiven.io>
Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/CA%2BhUKGKNX_%3Df%2B1C4r06WETKTq0G4Z_7q4L4Fxn5WWpMycDj9Fw%40mail.gmail.com

src/backend/jit/llvm/llvmjit.c

@@ -85,8 +85,11 @@ LLVMTypeRef StructExprState;
 LLVMTypeRef StructAggState;
 LLVMTypeRef StructAggStatePerGroupData;
 LLVMTypeRef StructAggStatePerTransData;
+LLVMTypeRef StructPlanState;
 
 LLVMValueRef AttributeTemplate;
+LLVMValueRef ExecEvalSubroutineTemplate;
+LLVMValueRef ExecEvalBoolSubroutineTemplate;
 
 LLVMModuleRef llvm_types_module = NULL;
 
@@ -384,11 +387,7 @@ llvm_pg_var_type(const char *varname)
 	if (!v_srcvar)
 		elog(ERROR, "variable %s not in llvmjit_types.c", varname);
 
-	/* look at the contained type */
-	typ = LLVMTypeOf(v_srcvar);
-	Assert(typ != NULL && LLVMGetTypeKind(typ) == LLVMPointerTypeKind);
-	typ = LLVMGetElementType(typ);
-	Assert(typ != NULL);
+	typ = LLVMGlobalGetValueType(v_srcvar);
 
 	return typ;
 }
@@ -400,12 +399,14 @@ llvm_pg_var_type(const char *varname)
 LLVMTypeRef
 llvm_pg_var_func_type(const char *varname)
 {
-	LLVMTypeRef typ = llvm_pg_var_type(varname);
+	LLVMValueRef v_srcvar;
+	LLVMTypeRef typ;
+
+	v_srcvar = LLVMGetNamedFunction(llvm_types_module, varname);
+	if (!v_srcvar)
+		elog(ERROR, "function %s not in llvmjit_types.c", varname);
 
-	/* look at the contained type */
-	Assert(LLVMGetTypeKind(typ) == LLVMPointerTypeKind);
-	typ = LLVMGetElementType(typ);
-	Assert(typ != NULL && LLVMGetTypeKind(typ) == LLVMFunctionTypeKind);
+	typ = LLVMGetFunctionType(v_srcvar);
 
 	return typ;
 }
@@ -435,7 +436,7 @@ llvm_pg_func(LLVMModuleRef mod, const char *funcname)
 
 	v_fn = LLVMAddFunction(mod,
 						   funcname,
-						   LLVMGetElementType(LLVMTypeOf(v_srcfn)));
+						   LLVMGetFunctionType(v_srcfn));
 	llvm_copy_attributes(v_srcfn, v_fn);
 
 	return v_fn;
@@ -531,7 +532,7 @@ llvm_function_reference(LLVMJitContext *context,
 							fcinfo->flinfo->fn_oid);
 		v_fn = LLVMGetNamedGlobal(mod, funcname);
 		if (v_fn != 0)
-			return LLVMBuildLoad(builder, v_fn, "");
+			return l_load(builder, TypePGFunction, v_fn, "");
 
 		v_fn_addr = l_ptr_const(fcinfo->flinfo->fn_addr, TypePGFunction);
 
@@ -541,15 +542,15 @@ llvm_function_reference(LLVMJitContext *context,
 		LLVMSetLinkage(v_fn, LLVMPrivateLinkage);
 		LLVMSetUnnamedAddr(v_fn, true);
 
-		return LLVMBuildLoad(builder, v_fn, "");
+		return l_load(builder, TypePGFunction, v_fn, "");
 	}
 
 	/* check if function already has been added */
 	v_fn = LLVMGetNamedFunction(mod, funcname);
 	if (v_fn != 0)
 		return v_fn;
 
-	v_fn = LLVMAddFunction(mod, funcname, LLVMGetElementType(TypePGFunction));
+	v_fn = LLVMAddFunction(mod, funcname, LLVMGetFunctionType(AttributeTemplate));
 
 	return v_fn;
 }
@@ -801,12 +802,15 @@ llvm_session_initialize(void)
 	LLVMInitializeNativeAsmParser();
 
 	/*
-	 * When targeting an LLVM version with opaque pointers enabled by default,
-	 * turn them off for the context we build our code in.  We don't need to
-	 * do so for other contexts (e.g. llvm_ts_context).  Once the IR is
-	 * generated, it carries the necessary information.
+	 * When targeting LLVM 15, turn off opaque pointers for the context we
+	 * build our code in.  We don't need to do so for other contexts (e.g.
+	 * llvm_ts_context).  Once the IR is generated, it carries the necessary
+	 * information.
+	 *
+	 * For 16 and above, opaque pointers must be used, and we have special
+	 * code for that.
 	 */
-#if LLVM_VERSION_MAJOR > 14
+#if LLVM_VERSION_MAJOR == 15
 	LLVMContextSetOpaquePointers(LLVMGetGlobalContext(), false);
 #endif
 
@@ -968,15 +972,7 @@ load_return_type(LLVMModuleRef mod, const char *name)
 	if (!value)
 		elog(ERROR, "function %s is unknown", name);
 
-	/* get type of function pointer */
-	typ = LLVMTypeOf(value);
-	Assert(typ != NULL);
-	/* dereference pointer */
-	typ = LLVMGetElementType(typ);
-	Assert(typ != NULL);
-	/* and look at return type */
-	typ = LLVMGetReturnType(typ);
-	Assert(typ != NULL);
+	typ = LLVMGetFunctionReturnType(value); /* in llvmjit_wrap.cpp */
 
 	return typ;
 }
@@ -1031,12 +1027,17 @@ llvm_create_types(void)
 	StructHeapTupleTableSlot = llvm_pg_var_type("StructHeapTupleTableSlot");
 	StructMinimalTupleTableSlot = llvm_pg_var_type("StructMinimalTupleTableSlot");
 	StructHeapTupleData = llvm_pg_var_type("StructHeapTupleData");
+	StructHeapTupleHeaderData = llvm_pg_var_type("StructHeapTupleHeaderData");
 	StructTupleDescData = llvm_pg_var_type("StructTupleDescData");
 	StructAggState = llvm_pg_var_type("StructAggState");
 	StructAggStatePerGroupData = llvm_pg_var_type("StructAggStatePerGroupData");
 	StructAggStatePerTransData = llvm_pg_var_type("StructAggStatePerTransData");
+	StructPlanState = llvm_pg_var_type("StructPlanState");
+	StructMinimalTupleData = llvm_pg_var_type("StructMinimalTupleData");
 
 	AttributeTemplate = LLVMGetNamedFunction(llvm_types_module, "AttributeTemplate");
+	ExecEvalSubroutineTemplate = LLVMGetNamedFunction(llvm_types_module, "ExecEvalSubroutineTemplate");
+	ExecEvalBoolSubroutineTemplate = LLVMGetNamedFunction(llvm_types_module, "ExecEvalBoolSubroutineTemplate");
 }
 
 /*