compile.c: stop wrong peephole optimization when covearge is enabled

jump-jump optimization ignores the event flags of the jump instruction
being skipped, which leads to overlook of line events.

This changeset stops the wrong optimization when coverage measurement is
neabled and when the jump instruction has any event flag.

Note that this issue is not only for coverage but also for TracePoint,
and this change does not fix TracePoint.
However, fixing it fundamentally is tough (which requires revamp of
the compiler).  This issue is critical in terms of coverage measurement,
but minor for TracePoint (ko1 said), so we here choose a stopgap
measurement.

[Bug #15980] [Bug #16397]

Note for backporters: this changeset can be viewed by `git diff -w`.

1 files changed, 129 insertions, 103 deletions

diff --git a/compile.c b/compile.c
index 0b808342c0..e261a38d7d 100644
--- a/compile.c
+++ b/compile.c
@@ -2861,109 +2861,135 @@ iseq_peephole_optimize(rb_iseq_t *iseq, LINK_ELEMENT *list, const int do_tailcal
 	 *   if L2
 	 */
 	INSN *nobj = (INSN *)get_destination_insn(iobj);
-	INSN *pobj = (INSN *)iobj->link.prev;
-	int prev_dup = 0;
-	if (pobj) {
-	    if (!IS_INSN(&pobj->link))
-		pobj = 0;
-	    else if (IS_INSN_ID(pobj, dup))
-		prev_dup = 1;
-	}
-
-	for (;;) {
-	    if (IS_INSN_ID(nobj, jump)) {
-		replace_destination(iobj, nobj);
-	    }
-	    else if (prev_dup && IS_INSN_ID(nobj, dup) &&
-		     !!(nobj = (INSN *)nobj->link.next) &&
-		     /* basic blocks, with no labels in the middle */
-		     nobj->insn_id == iobj->insn_id) {
-		/*
-		 *   dup
-		 *   if L1
-		 *   ...
-		 * L1:
-		 *   dup
-		 *   if L2
-		 * =>
-		 *   dup
-		 *   if L2
-		 *   ...
-		 * L1:
-		 *   dup
-		 *   if L2
-		 */
-		replace_destination(iobj, nobj);
-	    }
-	    else if (pobj) {
-		/*
-		 *   putnil
-		 *   if L1
-		 * =>
-		 *   # nothing
-		 *
-		 *   putobject true
-		 *   if L1
-		 * =>
-		 *   jump L1
-		 *
-		 *   putstring ".."
-		 *   if L1
-		 * =>
-		 *   jump L1
-		 *
-		 *   putstring ".."
-		 *   dup
-		 *   if L1
-		 * =>
-		 *   putstring ".."
-		 *   jump L1
-		 *
-		 */
-		int cond;
-		if (prev_dup && IS_INSN(pobj->link.prev)) {
-		    pobj = (INSN *)pobj->link.prev;
-		}
-		if (IS_INSN_ID(pobj, putobject)) {
-		    cond = (IS_INSN_ID(iobj, branchif) ?
-			    OPERAND_AT(pobj, 0) != Qfalse :
-			    IS_INSN_ID(iobj, branchunless) ?
-			    OPERAND_AT(pobj, 0) == Qfalse :
-			    FALSE);
-		}
-		else if (IS_INSN_ID(pobj, putstring) ||
-			 IS_INSN_ID(pobj, duparray) ||
-			 IS_INSN_ID(pobj, newarray)) {
-		    cond = IS_INSN_ID(iobj, branchif);
-		}
-		else if (IS_INSN_ID(pobj, putnil)) {
-		    cond = !IS_INSN_ID(iobj, branchif);
-		}
-		else break;
-		if (prev_dup || !IS_INSN_ID(pobj, newarray)) {
-		    ELEM_REMOVE(iobj->link.prev);
-		}
-		else if (!iseq_pop_newarray(iseq, pobj)) {
-		    pobj = new_insn_core(iseq, pobj->insn_info.line_no, BIN(pop), 0, NULL);
-                    ELEM_INSERT_PREV(&iobj->link, &pobj->link);
-		}
-		if (cond) {
-		    if (prev_dup) {
-			pobj = new_insn_core(iseq, pobj->insn_info.line_no, BIN(putnil), 0, NULL);
-			ELEM_INSERT_NEXT(&iobj->link, &pobj->link);
-		    }
-		    iobj->insn_id = BIN(jump);
-		    goto again;
-		}
-		else {
-		    unref_destination(iobj, 0);
-		    ELEM_REMOVE(&iobj->link);
-		}
-		break;
-	    }
-	    else break;
-	    nobj = (INSN *)get_destination_insn(nobj);
-	}
+
+        /* This is super nasty hack!!!
+         *
+         * This jump-jump optimization may ignore event flags of the jump
+         * instruction being skipped.  Actually, Line 2 TracePoint event
+         * is never fired in the following code:
+         *
+         *   1: raise if 1 == 2
+         *   2: while true
+         *   3:   break
+         *   4: end
+         *
+         * This is critical for coverage measurement.  [Bug #15980]
+         *
+         * This is a stopgap measure: stop the jump-jump optimization if
+         * coverage measurement is enabled and if the skipped instruction
+         * has any event flag.
+         *
+         * Note that, still, TracePoint Line event does not occur on Line 2.
+         * This should be fixed in future.
+         */
+        int stop_optimization =
+	    ISEQ_COVERAGE(iseq) && ISEQ_LINE_COVERAGE(iseq) &&
+            nobj->insn_info.events;
+	if (!stop_optimization) {
+            INSN *pobj = (INSN *)iobj->link.prev;
+            int prev_dup = 0;
+            if (pobj) {
+                if (!IS_INSN(&pobj->link))
+                    pobj = 0;
+                else if (IS_INSN_ID(pobj, dup))
+                    prev_dup = 1;
+            }
+
+            for (;;) {
+                if (IS_INSN_ID(nobj, jump)) {
+                    replace_destination(iobj, nobj);
+                }
+                else if (prev_dup && IS_INSN_ID(nobj, dup) &&
+                         !!(nobj = (INSN *)nobj->link.next) &&
+                         /* basic blocks, with no labels in the middle */
+                         nobj->insn_id == iobj->insn_id) {
+                    /*
+                     *   dup
+                     *   if L1
+                     *   ...
+                     * L1:
+                     *   dup
+                     *   if L2
+                     * =>
+                     *   dup
+                     *   if L2
+                     *   ...
+                     * L1:
+                     *   dup
+                     *   if L2
+                     */
+                    replace_destination(iobj, nobj);
+                }
+                else if (pobj) {
+                    /*
+                     *   putnil
+                     *   if L1
+                     * =>
+                     *   # nothing
+                     *
+                     *   putobject true
+                     *   if L1
+                     * =>
+                     *   jump L1
+                     *
+                     *   putstring ".."
+                     *   if L1
+                     * =>
+                     *   jump L1
+                     *
+                     *   putstring ".."
+                     *   dup
+                     *   if L1
+                     * =>
+                     *   putstring ".."
+                     *   jump L1
+                     *
+                     */
+                    int cond;
+                    if (prev_dup && IS_INSN(pobj->link.prev)) {
+                        pobj = (INSN *)pobj->link.prev;
+                    }
+                    if (IS_INSN_ID(pobj, putobject)) {
+                        cond = (IS_INSN_ID(iobj, branchif) ?
+                                OPERAND_AT(pobj, 0) != Qfalse :
+                                IS_INSN_ID(iobj, branchunless) ?
+                                OPERAND_AT(pobj, 0) == Qfalse :
+                                FALSE);
+                    }
+                    else if (IS_INSN_ID(pobj, putstring) ||
+                             IS_INSN_ID(pobj, duparray) ||
+                             IS_INSN_ID(pobj, newarray)) {
+                        cond = IS_INSN_ID(iobj, branchif);
+                    }
+                    else if (IS_INSN_ID(pobj, putnil)) {
+                        cond = !IS_INSN_ID(iobj, branchif);
+                    }
+                    else break;
+                    if (prev_dup || !IS_INSN_ID(pobj, newarray)) {
+                        ELEM_REMOVE(iobj->link.prev);
+                    }
+                    else if (!iseq_pop_newarray(iseq, pobj)) {
+                        pobj = new_insn_core(iseq, pobj->insn_info.line_no, BIN(pop), 0, NULL);
+                        ELEM_INSERT_PREV(&iobj->link, &pobj->link);
+                    }
+                    if (cond) {
+                        if (prev_dup) {
+                            pobj = new_insn_core(iseq, pobj->insn_info.line_no, BIN(putnil), 0, NULL);
+                            ELEM_INSERT_NEXT(&iobj->link, &pobj->link);
+                        }
+                        iobj->insn_id = BIN(jump);
+                        goto again;
+                    }
+                    else {
+                        unref_destination(iobj, 0);
+                        ELEM_REMOVE(&iobj->link);
+                    }
+                    break;
+                }
+                else break;
+                nobj = (INSN *)get_destination_insn(nobj);
+            }
+        }
     }
 
     if (IS_INSN_ID(iobj, pop)) {