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First stage of loop optimization (371802, r=igor).
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brendan%mozilla.org
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7bf5f8b7a1
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187827fa7f
@ -4155,32 +4155,52 @@ js_EmitTree(JSContext *cx, JSCodeGenerator *cg, JSParseNode *pn)
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break;
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case TOK_WHILE:
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/*
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* Minimize bytecodes issued for one or more iterations by jumping to
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* the condition below the body and closing the loop if the condition
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* is true with a backward branch. For iteration count i:
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*
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* i test at the top test at the bottom
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* = =============== ==================
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* 0 ifeq-pass goto; ifne-fail
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* 1 ifeq-fail; goto; ifne-pass goto; ifne-pass; ifne-fail
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* 2 2*(ifeq-fail; goto); ifeq-pass goto; 2*ifne-pass; ifne-fail
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* . . .
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* N N*(ifeq-fail; goto); ifeq-pass goto; N*ifne-pass; ifne-fail
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*
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* SpiderMonkey, pre-mozilla.org, emitted while parsing and so used
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* test at the top. When JSParseNode trees were added during the ES3
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* work (1998-9), the code generation scheme was not optimized, and
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* the decompiler continued to take advantage of the branch and jump
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* that bracketed the body. But given the SRC_WHILE note, it is easy
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* to support the more efficient scheme.
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*/
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js_PushStatement(&cg->treeContext, &stmtInfo, STMT_WHILE_LOOP, top);
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if (!js_EmitTree(cx, cg, pn->pn_left))
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return JS_FALSE;
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noteIndex = js_NewSrcNote(cx, cg, SRC_WHILE);
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if (noteIndex < 0)
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return JS_FALSE;
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beq = EmitJump(cx, cg, JSOP_IFEQ, 0);
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if (beq < 0)
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return JS_FALSE;
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if (!js_EmitTree(cx, cg, pn->pn_right))
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return JS_FALSE;
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jmp = EmitJump(cx, cg, JSOP_GOTO, top - CG_OFFSET(cg));
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jmp = EmitJump(cx, cg, JSOP_GOTO, 0);
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if (jmp < 0)
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return JS_FALSE;
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CHECK_AND_SET_JUMP_OFFSET_AT(cx, cg, beq);
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if (!js_SetSrcNoteOffset(cx, cg, noteIndex, 0, jmp - beq))
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top = CG_OFFSET(cg);
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if (!js_EmitTree(cx, cg, pn->pn_right))
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return JS_FALSE;
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CHECK_AND_SET_JUMP_OFFSET_AT(cx, cg, jmp);
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if (!js_EmitTree(cx, cg, pn->pn_left))
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return JS_FALSE;
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beq = EmitJump(cx, cg, JSOP_IFNE, top - CG_OFFSET(cg));
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if (beq < 0)
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return JS_FALSE;
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if (!js_SetSrcNoteOffset(cx, cg, noteIndex, 0, beq - jmp))
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return JS_FALSE;
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ok = js_PopStatementCG(cx, cg);
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break;
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case TOK_DO:
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/* Emit an annotated nop so we know to decompile a 'do' keyword. */
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if (js_NewSrcNote(cx, cg, SRC_WHILE) < 0 ||
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js_Emit1(cx, cg, JSOP_NOP) < 0) {
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noteIndex = js_NewSrcNote(cx, cg, SRC_WHILE);
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if (noteIndex < 0 || js_Emit1(cx, cg, JSOP_NOP) < 0)
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return JS_FALSE;
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}
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/* Compile the loop body. */
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top = CG_OFFSET(cg);
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@ -4199,12 +4219,14 @@ js_EmitTree(JSContext *cx, JSCodeGenerator *cg, JSParseNode *pn)
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return JS_FALSE;
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/*
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* No source note needed, because JSOP_IFNE is used only for do-while.
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* If we ever use JSOP_IFNE for other purposes, we can still avoid yet
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* another note here, by storing (jmp - top) in the SRC_WHILE note's
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* offset, and fetching that delta in order to decompile recursively.
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* Since we use JSOP_IFNE for other purposes as well as for do-while
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* loops, we must store 1 + (beq - top) in the SRC_WHILE note offset,
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* and the decompiler must get that delta and decompile recursively.
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*/
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if (EmitJump(cx, cg, JSOP_IFNE, top - CG_OFFSET(cg)) < 0)
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beq = EmitJump(cx, cg, JSOP_IFNE, top - CG_OFFSET(cg));
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if (beq < 0)
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return JS_FALSE;
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if (!js_SetSrcNoteOffset(cx, cg, noteIndex, 0, 1 + (beq - top)))
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return JS_FALSE;
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ok = js_PopStatementCG(cx, cg);
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break;
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@ -1791,8 +1791,18 @@ Decompile(SprintStack *ss, jsbytecode *pc, intN nb)
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todo = -2;
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switch (sn ? SN_TYPE(sn) : SRC_NULL) {
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case SRC_WHILE:
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++pc;
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tail = js_GetSrcNoteOffset(sn, 0) - 1;
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LOCAL_ASSERT(pc[tail] == JSOP_IFNE ||
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pc[tail] == JSOP_IFNEX);
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js_printf(SET_MAYBE_BRACE(jp), "\tdo {\n");
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jp->indent += 4;
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DECOMPILE_CODE(pc, tail);
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jp->indent -= 4;
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js_printf(jp, "\t} while (%s);\n", POP_STR());
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pc += tail;
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len = js_CodeSpec[*pc].length;
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todo = -2;
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break;
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case SRC_FOR:
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@ -2571,6 +2581,22 @@ Decompile(SprintStack *ss, jsbytecode *pc, intN nb)
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case JSOP_GOTOX:
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sn = js_GetSrcNote(jp->script, pc);
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switch (sn ? SN_TYPE(sn) : SRC_NULL) {
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case SRC_WHILE:
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cond = GetJumpOffset(pc, pc);
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tail = js_GetSrcNoteOffset(sn, 0);
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DECOMPILE_CODE(pc + cond, tail - cond);
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rval = POP_STR();
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js_printf(SET_MAYBE_BRACE(jp), "\twhile (%s) {\n", rval);
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jp->indent += 4;
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DECOMPILE_CODE(pc + oplen, cond - oplen);
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jp->indent -= 4;
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js_printf(jp, "\t}\n");
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pc += tail;
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LOCAL_ASSERT(*pc == JSOP_IFNE || *pc == JSOP_IFNEX);
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len = js_CodeSpec[*pc].length;
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todo = -2;
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break;
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case SRC_CONT2LABEL:
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atom = js_GetAtom(cx, &jp->script->atomMap,
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(jsatomid) js_GetSrcNoteOffset(sn, 0));
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@ -2580,9 +2606,11 @@ Decompile(SprintStack *ss, jsbytecode *pc, intN nb)
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RETRACT(&ss->sprinter, rval);
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js_printf(jp, "\tcontinue %s;\n", rval);
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break;
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case SRC_CONTINUE:
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js_printf(jp, "\tcontinue;\n");
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break;
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case SRC_BREAK2LABEL:
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atom = js_GetAtom(cx, &jp->script->atomMap,
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(jsatomid) js_GetSrcNoteOffset(sn, 0));
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@ -2592,8 +2620,10 @@ Decompile(SprintStack *ss, jsbytecode *pc, intN nb)
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RETRACT(&ss->sprinter, rval);
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js_printf(jp, "\tbreak %s;\n", rval);
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break;
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case SRC_HIDDEN:
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break;
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default:
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js_printf(jp, "\tbreak;\n");
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break;
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@ -2667,17 +2697,6 @@ Decompile(SprintStack *ss, jsbytecode *pc, intN nb)
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todo = -2;
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break;
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case SRC_WHILE:
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rval = POP_STR();
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js_printf(SET_MAYBE_BRACE(jp), "\twhile (%s) {\n", rval);
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jp->indent += 4;
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tail = js_GetSrcNoteOffset(sn, 0);
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DECOMPILE_CODE(pc + oplen, tail - oplen);
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jp->indent -= 4;
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js_printf(jp, "\t}\n");
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todo = -2;
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break;
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case SRC_COND:
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xval = JS_strdup(cx, POP_STR());
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if (!xval)
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@ -2709,10 +2728,7 @@ Decompile(SprintStack *ss, jsbytecode *pc, intN nb)
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case JSOP_IFNE:
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case JSOP_IFNEX:
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/* Currently, this must be a do-while loop's upward branch. */
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jp->indent -= 4;
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js_printf(jp, "\t} while (%s);\n", POP_STR());
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todo = -2;
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LOCAL_ASSERT(0);
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break;
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case JSOP_OR:
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@ -200,7 +200,7 @@ JS_XDRFindClassById(JSXDRState *xdr, uint32 id);
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* before deserialization of bytecode. If the saved version does not match
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* the current version, abort deserialization and invalidate the file.
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*/
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#define JSXDR_BYTECODE_VERSION (0xb973c0de - 5)
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#define JSXDR_BYTECODE_VERSION (0xb973c0de - 6)
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/*
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* Library-private functions.
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