Simplify executor's handling of CaseTestExpr & CoerceToDomainValue.

Instead of deciding at runtime whether to read from casetest.value
or caseValue_datum, split EEOP_CASE_TESTVAL into two opcodes and
make the decision during expression compilation.  Similarly for
EEOP_DOMAIN_TESTVAL.  This actually results in net less code,
mainly because llvmjit_expr.c's code for handling these opcodes
gets shorter.  The performance gain is doubtless negligible, but
this seems worth changing anyway on grounds of simplicity and
understandability.

Author: Andreas Karlsson <andreas@proxel.se>
Co-authored-by: Xing Guo <higuoxing@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CACpMh+AiBYAWn+D1aU7Rsy-V1tox06Cbc0H3qA7rwL5zdJ=anQ@mail.gmail.com

2 files changed, 45 insertions, 48 deletions

diff --git a/src/backend/executor/execExpr.c b/src/backend/executor/execExpr.c
index 8f28da4bf94..03566c4d181 100644
--- a/src/backend/executor/execExpr.c
+++ b/src/backend/executor/execExpr.c
@@ -1901,13 +1901,17 @@ ExecInitExprRec(Expr *node, ExprState *state,
 				 * actually within a CaseExpr, ArrayCoerceExpr, etc structure.
 				 * That can happen because some parts of the system abuse
 				 * CaseTestExpr to cause a read of a value externally supplied
-				 * in econtext->caseValue_datum.  We'll take care of that
-				 * scenario at runtime.
+				 * in econtext->caseValue_datum.  We'll take care of that by
+				 * generating a specialized operation.
 				 */
-				scratch.opcode = EEOP_CASE_TESTVAL;
-				scratch.d.casetest.value = state->innermost_caseval;
-				scratch.d.casetest.isnull = state->innermost_casenull;
-
+				if (state->innermost_caseval == NULL)
+					scratch.opcode = EEOP_CASE_TESTVAL_EXT;
+				else
+				{
+					scratch.opcode = EEOP_CASE_TESTVAL;
+					scratch.d.casetest.value = state->innermost_caseval;
+					scratch.d.casetest.isnull = state->innermost_casenull;
+				}
 				ExprEvalPushStep(state, &scratch);
 				break;
 			}
@@ -2594,14 +2598,18 @@ ExecInitExprRec(Expr *node, ExprState *state,
 				 * that innermost_domainval could be NULL, if we're compiling
 				 * a standalone domain check rather than one embedded in a
 				 * larger expression.  In that case we must read from
-				 * econtext->domainValue_datum.  We'll take care of that
-				 * scenario at runtime.
+				 * econtext->domainValue_datum.  We'll take care of that by
+				 * generating a specialized operation.
 				 */
-				scratch.opcode = EEOP_DOMAIN_TESTVAL;
-				/* we share instruction union variant with case testval */
-				scratch.d.casetest.value = state->innermost_domainval;
-				scratch.d.casetest.isnull = state->innermost_domainnull;
-
+				if (state->innermost_domainval == NULL)
+					scratch.opcode = EEOP_DOMAIN_TESTVAL_EXT;
+				else
+				{
+					scratch.opcode = EEOP_DOMAIN_TESTVAL;
+					/* we share instruction union variant with case testval */
+					scratch.d.casetest.value = state->innermost_domainval;
+					scratch.d.casetest.isnull = state->innermost_domainnull;
+				}
 				ExprEvalPushStep(state, &scratch);
 				break;
 			}
diff --git a/src/backend/executor/execExprInterp.c b/src/backend/executor/execExprInterp.c
index 1127e6f11eb..09f6a5f14c1 100644
--- a/src/backend/executor/execExprInterp.c
+++ b/src/backend/executor/execExprInterp.c
@@ -365,8 +365,7 @@ ExecReadyInterpretedExpr(ExprState *state)
 			return;
 		}
 		else if (step0 == EEOP_CASE_TESTVAL &&
-				 step1 == EEOP_FUNCEXPR_STRICT &&
-				 state->steps[0].d.casetest.value)
+				 step1 == EEOP_FUNCEXPR_STRICT)
 		{
 			state->evalfunc_private = ExecJustApplyFuncToCase;
 			return;
@@ -524,6 +523,7 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
 		&&CASE_EEOP_PARAM_CALLBACK,
 		&&CASE_EEOP_PARAM_SET,
 		&&CASE_EEOP_CASE_TESTVAL,
+		&&CASE_EEOP_CASE_TESTVAL_EXT,
 		&&CASE_EEOP_MAKE_READONLY,
 		&&CASE_EEOP_IOCOERCE,
 		&&CASE_EEOP_IOCOERCE_SAFE,
@@ -548,6 +548,7 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
 		&&CASE_EEOP_SBSREF_ASSIGN,
 		&&CASE_EEOP_SBSREF_FETCH,
 		&&CASE_EEOP_DOMAIN_TESTVAL,
+		&&CASE_EEOP_DOMAIN_TESTVAL_EXT,
 		&&CASE_EEOP_DOMAIN_NOTNULL,
 		&&CASE_EEOP_DOMAIN_CHECK,
 		&&CASE_EEOP_HASHDATUM_SET_INITVAL,
@@ -1273,44 +1274,16 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
 
 		EEO_CASE(EEOP_CASE_TESTVAL)
 		{
-			/*
-			 * Normally upper parts of the expression tree have setup the
-			 * values to be returned here, but some parts of the system
-			 * currently misuse {caseValue,domainValue}_{datum,isNull} to set
-			 * run-time data.  So if no values have been set-up, use
-			 * ExprContext's.  This isn't pretty, but also not *that* ugly,
-			 * and this is unlikely to be performance sensitive enough to
-			 * worry about an extra branch.
-			 */
-			if (op->d.casetest.value)
-			{
-				*op->resvalue = *op->d.casetest.value;
-				*op->resnull = *op->d.casetest.isnull;
-			}
-			else
-			{
-				*op->resvalue = econtext->caseValue_datum;
-				*op->resnull = econtext->caseValue_isNull;
-			}
+			*op->resvalue = *op->d.casetest.value;
+			*op->resnull = *op->d.casetest.isnull;
 
 			EEO_NEXT();
 		}
 
-		EEO_CASE(EEOP_DOMAIN_TESTVAL)
+		EEO_CASE(EEOP_CASE_TESTVAL_EXT)
 		{
-			/*
-			 * See EEOP_CASE_TESTVAL comment.
-			 */
-			if (op->d.casetest.value)
-			{
-				*op->resvalue = *op->d.casetest.value;
-				*op->resnull = *op->d.casetest.isnull;
-			}
-			else
-			{
-				*op->resvalue = econtext->domainValue_datum;
-				*op->resnull = econtext->domainValue_isNull;
-			}
+			*op->resvalue = econtext->caseValue_datum;
+			*op->resnull = econtext->caseValue_isNull;
 
 			EEO_NEXT();
 		}
@@ -1726,6 +1699,22 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
 			EEO_NEXT();
 		}
 
+		EEO_CASE(EEOP_DOMAIN_TESTVAL)
+		{
+			*op->resvalue = *op->d.casetest.value;
+			*op->resnull = *op->d.casetest.isnull;
+
+			EEO_NEXT();
+		}
+
+		EEO_CASE(EEOP_DOMAIN_TESTVAL_EXT)
+		{
+			*op->resvalue = econtext->domainValue_datum;
+			*op->resnull = econtext->domainValue_isNull;
+
+			EEO_NEXT();
+		}
+
 		EEO_CASE(EEOP_DOMAIN_NOTNULL)
 		{
 			/* too complex for an inline implementation */