planner: remove the unnecessary skip-plan-cache flag in StmtCtx

expression/builtin_compare.go

@@ -1586,7 +1586,7 @@ func (c *compareFunctionClass) refineArgs(ctx sessionctx.Context, args []Express
 		} else {
 			return args
 		}
-	} else if ctx.GetSessionVars().StmtCtx.SkipPlanCache {
+	} else if !ctx.GetSessionVars().StmtCtx.UseCache {
 		// We should remove the mutable constant for correctness, because its value may be changed.
 		RemoveMutableConst(ctx, args)
 	}

expression/util.go

@@ -1241,7 +1241,7 @@ func ContainCorrelatedColumn(exprs []Expression) bool {
 // TODO: Do more careful check here.
 func MaybeOverOptimized4PlanCache(ctx sessionctx.Context, exprs []Expression) bool {
 	// If we do not enable plan cache, all the optimization can work correctly.
-	if !ctx.GetSessionVars().StmtCtx.UseCache || ctx.GetSessionVars().StmtCtx.SkipPlanCache {
+	if !ctx.GetSessionVars().StmtCtx.UseCache {
 		return false
 	}
 	return containMutableConst(ctx, exprs)

planner/core/expression_rewriter.go

@@ -1567,7 +1567,7 @@ func (er *expressionRewriter) inToExpression(lLen int, not bool, tp *types.Field
 					} else {
 						continue
 					}
-				} else if er.sctx.GetSessionVars().StmtCtx.SkipPlanCache {
+				} else if !er.sctx.GetSessionVars().StmtCtx.UseCache {
 					// We should remove the mutable constant for correctness, because its value may be changed.
 					expression.RemoveMutableConst(er.sctx, []expression.Expression{c})
 				}

planner/core/plan_cache.go

@@ -280,7 +280,7 @@ func generateNewPlan(ctx context.Context, sctx sessionctx.Context, isNonPrepared
 	if containTableDual(p) && paramNum > 0 {
 		stmtCtx.SetSkipPlanCache(errors.New("skip plan-cache: get a TableDual plan"))
 	}
-	if stmtAst.UseCache && !stmtCtx.SkipPlanCache && !ignorePlanCache {
+	if stmtCtx.UseCache && !ignorePlanCache {
 		// rebuild key to exclude kv.TiFlash when stmt is not read only
 		if _, isolationReadContainTiFlash := sessVars.IsolationReadEngines[kv.TiFlash]; isolationReadContainTiFlash && !IsReadOnly(stmtAst.Stmt, sessVars) {
 			delete(sessVars.IsolationReadEngines, kv.TiFlash)
@@ -640,7 +640,7 @@ func CheckPreparedPriv(sctx sessionctx.Context, stmt *PlanCacheStmt, is infosche
 // short paths for these executions, currently "point select" and "point update"
 func tryCachePointPlan(_ context.Context, sctx sessionctx.Context,
 	stmt *PlanCacheStmt, _ infoschema.InfoSchema, p Plan) error {
-	if !sctx.GetSessionVars().StmtCtx.UseCache || sctx.GetSessionVars().StmtCtx.SkipPlanCache {
+	if !sctx.GetSessionVars().StmtCtx.UseCache {
 		return nil
 	}
 	var (

sessionctx/stmtctx/stmtctx.go

@@ -172,7 +172,6 @@ type StatementContext struct {
 	InNullRejectCheck             bool
 	AllowInvalidDate              bool
 	IgnoreNoPartition             bool
-	SkipPlanCache                 bool
 	IgnoreExplainIDSuffix         bool
 	SkipUTF8Check                 bool
 	SkipASCIICheck                bool
@@ -611,10 +610,10 @@ func (sc *StatementContext) SetPlanHint(hint string) {
 
 // SetSkipPlanCache sets to skip the plan cache and records the reason.
 func (sc *StatementContext) SetSkipPlanCache(reason error) {
-	if sc.UseCache && sc.SkipPlanCache {
+	if !sc.UseCache {
 		return // avoid unnecessary warnings
 	}
-	sc.SkipPlanCache = true
+	sc.UseCache = false
 	sc.AppendWarning(reason)
 }