From 07c7ff996706c6f71e00d76894845c1f87956472 Mon Sep 17 00:00:00 2001
From: soumyadeep2007 <sochakraborty@pivotal.io>
Date: Sun, 27 Oct 2019 17:42:53 -0700
Subject: [PATCH v1] Resolve PL handler names for JITed code instead of using
 const pointers

Using const pointers to PL handler functions prevents optimization
opportunities in JITed code. Now fmgr_symbol() resolves PL function
references to the corresponding language's handler.
llvm_function_reference() now no longer needs to create the global to
such a function.

Discussion: https://postgr.es/m/20191024224303.jvdx3hq3ak2vbit3%40alap3.anarazel.de:wq
---
 src/backend/jit/llvm/llvmjit.c | 29 +++--------------------------
 src/backend/utils/fmgr/fmgr.c  | 30 +++++++++++++++++++++++-------
 2 files changed, 26 insertions(+), 33 deletions(-)

diff --git a/src/backend/jit/llvm/llvmjit.c b/src/backend/jit/llvm/llvmjit.c
index 82c4afb701..69a4167ac9 100644
--- a/src/backend/jit/llvm/llvmjit.c
+++ b/src/backend/jit/llvm/llvmjit.c
@@ -369,38 +369,15 @@ llvm_function_reference(LLVMJitContext *context,
 
 	fmgr_symbol(fcinfo->flinfo->fn_oid, &modname, &basename);
 
-	if (modname != NULL && basename != NULL)
+	if (modname != NULL)
 	{
 		/* external function in loadable library */
 		funcname = psprintf("pgextern.%s.%s", modname, basename);
 	}
-	else if (basename != NULL)
-	{
-		/* internal function */
-		funcname = psprintf("%s", basename);
-	}
 	else
 	{
-		/*
-		 * Function we don't know to handle, return pointer. We do so by
-		 * creating a global constant containing a pointer to the function.
-		 * Makes IR more readable.
-		 */
-		LLVMValueRef v_fn_addr;
-
-		funcname = psprintf("pgoidextern.%u",
-							fcinfo->flinfo->fn_oid);
-		v_fn = LLVMGetNamedGlobal(mod, funcname);
-		if (v_fn != 0)
-			return LLVMBuildLoad(builder, v_fn, "");
-
-		v_fn_addr = l_ptr_const(fcinfo->flinfo->fn_addr, TypePGFunction);
-
-		v_fn = LLVMAddGlobal(mod, TypePGFunction, funcname);
-		LLVMSetInitializer(v_fn, v_fn_addr);
-		LLVMSetGlobalConstant(v_fn, true);
-
-		return LLVMBuildLoad(builder, v_fn, "");
+		/* internal function or a PL handler */
+		funcname = psprintf("%s", basename);
 	}
 
 	/* check if function already has been added */
diff --git a/src/backend/utils/fmgr/fmgr.c b/src/backend/utils/fmgr/fmgr.c
index 099ebd779b..71398bb3c1 100644
--- a/src/backend/utils/fmgr/fmgr.c
+++ b/src/backend/utils/fmgr/fmgr.c
@@ -265,11 +265,9 @@ fmgr_info_cxt_security(Oid functionId, FmgrInfo *finfo, MemoryContext mcxt,
 /*
  * Return module and C function name providing implementation of functionId.
  *
- * If *mod == NULL and *fn == NULL, no C symbol is known to implement
- * function.
- *
  * If *mod == NULL and *fn != NULL, the function is implemented by a symbol in
- * the main binary.
+ * the main binary. If the function being looked up is not a C language
+ * function, it's language handler name is returned.
  *
  * If *mod != NULL and *fn !=NULL the function is implemented in an extension
  * shared object.
@@ -285,6 +283,11 @@ fmgr_symbol(Oid functionId, char **mod, char **fn)
 	bool		isnull;
 	Datum		prosrcattr;
 	Datum		probinattr;
+	Oid			language;
+	HeapTuple	languageTuple;
+	Form_pg_language languageStruct;
+	HeapTuple	plHandlerProcedureTuple;
+	Form_pg_proc plHandlerProcedureStruct;
 
 	/* Otherwise we need the pg_proc entry */
 	procedureTuple = SearchSysCache1(PROCOID, ObjectIdGetDatum(functionId));
@@ -304,8 +307,9 @@ fmgr_symbol(Oid functionId, char **mod, char **fn)
 		return;
 	}
 
+	language = procedureStruct->prolang;
 	/* see fmgr_info_cxt_security for the individual cases */
-	switch (procedureStruct->prolang)
+	switch (language)
 	{
 		case INTERNALlanguageId:
 			prosrcattr = SysCacheGetAttr(PROCOID, procedureTuple,
@@ -342,9 +346,21 @@ fmgr_symbol(Oid functionId, char **mod, char **fn)
 			break;
 
 		default:
+			languageTuple = SearchSysCache1(LANGOID,
+											 ObjectIdGetDatum(language));
+			if (!HeapTupleIsValid(languageTuple))
+				elog(ERROR, "cache lookup failed for language %u", language);
+			languageStruct = (Form_pg_language) GETSTRUCT(languageTuple);
+			plHandlerProcedureTuple = SearchSysCache1(PROCOID,
+													  ObjectIdGetDatum(
+														  languageStruct->lanplcallfoid));
+			if (!HeapTupleIsValid(plHandlerProcedureTuple))
+				elog(ERROR, "cache lookup failed for function %u", functionId);
+			plHandlerProcedureStruct = (Form_pg_proc) GETSTRUCT(plHandlerProcedureTuple);
 			*mod = NULL;
-			*fn = NULL;			/* unknown, pass pointer */
-			break;
+			*fn = pstrdup(NameStr(plHandlerProcedureStruct->proname));
+			ReleaseSysCache(languageTuple);
+			ReleaseSysCache(plHandlerProcedureTuple);
 	}
 
 	ReleaseSysCache(procedureTuple);
-- 
2.23.0