Compute information about EEOP_*_FETCHSOME at expression init time.

Previously this information was computed when JIT compiling an
expression.  But the information is useful for assertions in the
non-JIT case too (for assertions), therefore it makes sense to move
it.

This will, in a followup commit, allow to treat different slot types
differently. E.g. for virtual slots there's no need to generate a JIT
function to deform the slot.

Author: Andres Freund
Discussion: https://postgr.es/m/20181105210039.hh4vvi4vwoq5ba2q@alap3.anarazel.de

src/backend/executor/execExpr.c

@@ -65,6 +65,7 @@ static void ExecInitFunc(ExprEvalStep *scratch, Expr *node, List *args,
 static void ExecInitExprSlots(ExprState *state, Node *node);
 static void ExecPushExprSlots(ExprState *state, LastAttnumInfo *info);
 static bool get_last_attnums_walker(Node *node, LastAttnumInfo *info);
+static void ExecComputeSlotInfo(ExprState *state, ExprEvalStep *op);
 static void ExecInitWholeRowVar(ExprEvalStep *scratch, Var *variable,
 					ExprState *state);
 static void ExecInitArrayRef(ExprEvalStep *scratch, ArrayRef *aref,
@@ -2288,21 +2289,30 @@ ExecPushExprSlots(ExprState *state, LastAttnumInfo *info)
 	{
 		scratch.opcode = EEOP_INNER_FETCHSOME;
 		scratch.d.fetch.last_var = info->last_inner;
+		scratch.d.fetch.fixed = false;
+		scratch.d.fetch.kind = NULL;
 		scratch.d.fetch.known_desc = NULL;
+		ExecComputeSlotInfo(state, &scratch);
 		ExprEvalPushStep(state, &scratch);
 	}
 	if (info->last_outer > 0)
 	{
 		scratch.opcode = EEOP_OUTER_FETCHSOME;
 		scratch.d.fetch.last_var = info->last_outer;
+		scratch.d.fetch.fixed = false;
+		scratch.d.fetch.kind = NULL;
 		scratch.d.fetch.known_desc = NULL;
+		ExecComputeSlotInfo(state, &scratch);
 		ExprEvalPushStep(state, &scratch);
 	}
 	if (info->last_scan > 0)
 	{
 		scratch.opcode = EEOP_SCAN_FETCHSOME;
 		scratch.d.fetch.last_var = info->last_scan;
+		scratch.d.fetch.fixed = false;
+		scratch.d.fetch.kind = NULL;
 		scratch.d.fetch.known_desc = NULL;
+		ExecComputeSlotInfo(state, &scratch);
 		ExprEvalPushStep(state, &scratch);
 	}
 }
@@ -2355,6 +2365,94 @@ get_last_attnums_walker(Node *node, LastAttnumInfo *info)
 								  (void *) info);
 }
 
+/*
+ * Compute additional information for EEOP_*_FETCHSOME ops.
+ *
+ * The goal is to determine whether a slot is 'fixed', that is, every
+ * evaluation of the the expression will have the same type of slot, with an
+ * equivalent descriptor.
+ */
+static void
+ExecComputeSlotInfo(ExprState *state, ExprEvalStep *op)
+{
+	PlanState *parent = state->parent;
+	TupleDesc	desc = NULL;
+	const TupleTableSlotOps *tts_ops = NULL;
+	bool isfixed = false;
+
+	if (op->d.fetch.known_desc != NULL)
+	{
+		desc = op->d.fetch.known_desc;
+		tts_ops = op->d.fetch.kind;
+		isfixed = op->d.fetch.kind != NULL;
+	}
+	else if (!parent)
+	{
+		isfixed = false;
+	}
+	else if (op->opcode == EEOP_INNER_FETCHSOME)
+	{
+		PlanState  *is = innerPlanState(parent);
+
+		if (parent->inneropsset && !parent->inneropsfixed)
+		{
+			isfixed = false;
+		}
+		else if (parent->inneropsset && parent->innerops)
+		{
+			isfixed = true;
+			tts_ops = parent->innerops;
+		}
+		else if (is)
+		{
+			tts_ops = ExecGetResultSlotOps(is, &isfixed);
+			desc = ExecGetResultType(is);
+		}
+	}
+	else if (op->opcode == EEOP_OUTER_FETCHSOME)
+	{
+		PlanState  *os = outerPlanState(parent);
+
+		if (parent->outeropsset && !parent->outeropsfixed)
+		{
+			isfixed = false;
+		}
+		else if (parent->outeropsset && parent->outerops)
+		{
+			isfixed = true;
+			tts_ops = parent->outerops;
+		}
+		else if (os)
+		{
+			tts_ops = ExecGetResultSlotOps(os, &isfixed);
+			desc = ExecGetResultType(os);
+		}
+	}
+	else if (op->opcode == EEOP_SCAN_FETCHSOME)
+	{
+		desc = parent->scandesc;
+
+		if (parent && parent->scanops)
+			tts_ops = parent->scanops;
+
+		if (parent->scanopsset)
+			isfixed = parent->scanopsfixed;
+	}
+
+	if (isfixed && desc != NULL && tts_ops != NULL)
+	{
+		op->d.fetch.fixed = true;
+		op->d.fetch.kind = tts_ops;
+		op->d.fetch.known_desc = desc;
+	}
+	else
+	{
+		op->d.fetch.fixed = false;
+		op->d.fetch.kind = NULL;
+		op->d.fetch.known_desc = NULL;
+	}
+}
+
 /*
  * Prepare step for the evaluation of a whole-row variable.
  * The caller still has to push the step.
@@ -3255,12 +3353,18 @@ ExecBuildGroupingEqual(TupleDesc ldesc, TupleDesc rdesc,
 	/* push deform steps */
 	scratch.opcode = EEOP_INNER_FETCHSOME;
 	scratch.d.fetch.last_var = maxatt;
+	scratch.d.fetch.fixed = false;
 	scratch.d.fetch.known_desc = ldesc;
+	scratch.d.fetch.kind = lops;
+	ExecComputeSlotInfo(state, &scratch);
 	ExprEvalPushStep(state, &scratch);
 
 	scratch.opcode = EEOP_OUTER_FETCHSOME;
 	scratch.d.fetch.last_var = maxatt;
+	scratch.d.fetch.fixed = false;
 	scratch.d.fetch.known_desc = rdesc;
+	scratch.d.fetch.kind = rops;
+	ExecComputeSlotInfo(state, &scratch);
 	ExprEvalPushStep(state, &scratch);
 
 	/*

src/backend/jit/llvm/llvmjit_expr.c

@@ -276,6 +276,8 @@ llvm_compile_expr(ExprState *state)
 					LLVMValueRef v_slot;
 					LLVMBasicBlockRef b_fetch;
 					LLVMValueRef v_nvalid;
+					LLVMValueRef l_jit_deform = NULL;
+					const TupleTableSlotOps *tts_ops = NULL;
 
 					b_fetch = l_bb_before_v(opblocks[i + 1],
 											"op.%d.fetch", i);
@@ -283,40 +285,22 @@ llvm_compile_expr(ExprState *state)
 					if (op->d.fetch.known_desc)
 						desc = op->d.fetch.known_desc;
 
+					if (op->d.fetch.fixed)
+						tts_ops = op->d.fetch.kind;
+
 					if (opcode == EEOP_INNER_FETCHSOME)
-					{
-						PlanState  *is = innerPlanState(parent);
-
 						v_slot = v_innerslot;
-
-						if (!desc &&
-							is &&
-							is->ps_ResultTupleSlot &&
-							TTS_FIXED(is->ps_ResultTupleSlot))
-							desc = is->ps_ResultTupleSlot->tts_tupleDescriptor;
-					}
 					else if (opcode == EEOP_OUTER_FETCHSOME)
-					{
-						PlanState  *os = outerPlanState(parent);
-
 						v_slot = v_outerslot;
-
-						if (!desc &&
-							os &&
-							os->ps_ResultTupleSlot &&
-							TTS_FIXED(os->ps_ResultTupleSlot))
-							desc = os->ps_ResultTupleSlot->tts_tupleDescriptor;
-					}
 					else
-					{
 						v_slot = v_scanslot;
-						if (!desc && parent)
-							desc = parent->scandesc;
-					}
 
 					/*
 					 * Check if all required attributes are available, or
 					 * whether deforming is required.
+					 *
+					 * TODO: skip nvalid check if slot is fixed and known to
+					 * be a virtual slot.
 					 */
 					v_nvalid =
 						l_load_struct_gep(b, v_slot,
@@ -336,19 +320,21 @@ llvm_compile_expr(ExprState *state)
 					 * function specific to tupledesc and the exact number of
 					 * to-be-extracted attributes.
 					 */
-					if (desc && (context->base.flags & PGJIT_DEFORM))
+					if (tts_ops && desc && (context->base.flags & PGJIT_DEFORM))
 					{
-						LLVMValueRef params[1];
-						LLVMValueRef l_jit_deform;
-
 						l_jit_deform =
 							slot_compile_deform(context, desc,
 												op->d.fetch.last_var);
+					}
+
+					if (l_jit_deform)
+					{
+						LLVMValueRef params[1];
+
 						params[0] = v_slot;
 
 						LLVMBuildCall(b, l_jit_deform,
 									  params, lengthof(params), "");
-
 					}
 					else
 					{

src/include/executor/execExpr.h

@@ -262,7 +262,12 @@ typedef struct ExprEvalStep
 		{
 			/* attribute number up to which to fetch (inclusive) */
 			int			last_var;
+			/* will the type of slot be the same for every invocation */
+			bool		fixed;
+			/* tuple descriptor, if known */
 			TupleDesc	known_desc;
+			/* type of slot, can only be relied upon if fixed is set */
+			const TupleTableSlotOps *kind;
 		}			fetch;
 
 		/* for EEOP_INNER/OUTER/SCAN_[SYS]VAR[_FIRST] */