Bug 704369: Move while emit. (r=Waldo)

js/src/frontend/BytecodeEmitter.cpp

@@ -5953,6 +5953,62 @@ EmitDo(JSContext *cx, BytecodeEmitter *bce, ParseNode *pn)
     return PopStatementBCE(cx, bce);
 }
 
+static bool
+EmitWhile(JSContext *cx, BytecodeEmitter *bce, ParseNode *pn, ptrdiff_t top)
+{
+    /*
+     * Minimize bytecodes issued for one or more iterations by jumping to
+     * the condition below the body and closing the loop if the condition
+     * is true with a backward branch. For iteration count i:
+     *
+     *  i    test at the top                 test at the bottom
+     *  =    ===============                 ==================
+     *  0    ifeq-pass                       goto; ifne-fail
+     *  1    ifeq-fail; goto; ifne-pass      goto; ifne-pass; ifne-fail
+     *  2    2*(ifeq-fail; goto); ifeq-pass  goto; 2*ifne-pass; ifne-fail
+     *  . . .
+     *  N    N*(ifeq-fail; goto); ifeq-pass  goto; N*ifne-pass; ifne-fail
+     *
+     * SpiderMonkey, pre-mozilla.org, emitted while parsing and so used
+     * test at the top. When ParseNode trees were added during the ES3
+     * work (1998-9), the code generation scheme was not optimized, and
+     * the decompiler continued to take advantage of the branch and jump
+     * that bracketed the body. But given the SRC_WHILE note, it is easy
+     * to support the more efficient scheme.
+     */
+    StmtInfo stmtInfo;
+    PushStatement(bce, &stmtInfo, STMT_WHILE_LOOP, top);
+    ptrdiff_t noteIndex = NewSrcNote(cx, bce, SRC_WHILE);
+    if (noteIndex < 0)
+        return JS_FALSE;
+    ptrdiff_t jmp = EmitJump(cx, bce, JSOP_GOTO, 0);
+    if (jmp < 0)
+        return JS_FALSE;
+    ptrdiff_t noteIndex2 = NewSrcNote(cx, bce, SRC_LOOPHEAD);
+    if (noteIndex2 < 0)
+        return JS_FALSE;
+    top = EmitTraceOp(cx, bce, pn->pn_right);
+    if (top < 0)
+        return JS_FALSE;
+    if (!EmitTree(cx, bce, pn->pn_right))
+        return JS_FALSE;
+    CHECK_AND_SET_JUMP_OFFSET_AT(cx, bce, jmp);
+    if (!EmitTree(cx, bce, pn->pn_left))
+        return JS_FALSE;
+    ptrdiff_t beq = EmitJump(cx, bce, JSOP_IFNE, top - bce->offset());
+    if (beq < 0)
+        return JS_FALSE;
+    /*
+     * Be careful: We must set noteIndex2 before noteIndex in case the noteIndex
+     * note gets bigger.
+     */
+    if (!SetSrcNoteOffset(cx, bce, noteIndex2, 0, beq - top))
+        return JS_FALSE;
+    if (!SetSrcNoteOffset(cx, bce, noteIndex, 0, beq - jmp))
+        return JS_FALSE;
+    return PopStatementBCE(cx, bce);
+}
+
 JSBool
 frontend::EmitTree(JSContext *cx, BytecodeEmitter *bce, ParseNode *pn)
 {
@@ -5963,7 +6019,7 @@ frontend::EmitTree(JSContext *cx, BytecodeEmitter *bce, ParseNode *pn)
     ParseNode *pn2, *pn3;
     JSAtom *atom;
     jsatomid atomIndex;
-    ptrdiff_t noteIndex, noteIndex2;
+    ptrdiff_t noteIndex;
     SrcNoteType noteType;
     jsbytecode *pc;
     JSOp op;
@@ -6018,56 +6074,7 @@ frontend::EmitTree(JSContext *cx, BytecodeEmitter *bce, ParseNode *pn)
         break;
 
       case PNK_WHILE:
-        /*
-         * Minimize bytecodes issued for one or more iterations by jumping to
-         * the condition below the body and closing the loop if the condition
-         * is true with a backward branch. For iteration count i:
-         *
-         *  i    test at the top                 test at the bottom
-         *  =    ===============                 ==================
-         *  0    ifeq-pass                       goto; ifne-fail
-         *  1    ifeq-fail; goto; ifne-pass      goto; ifne-pass; ifne-fail
-         *  2    2*(ifeq-fail; goto); ifeq-pass  goto; 2*ifne-pass; ifne-fail
-         *  . . .
-         *  N    N*(ifeq-fail; goto); ifeq-pass  goto; N*ifne-pass; ifne-fail
-         *
-         * SpiderMonkey, pre-mozilla.org, emitted while parsing and so used
-         * test at the top. When ParseNode trees were added during the ES3
-         * work (1998-9), the code generation scheme was not optimized, and
-         * the decompiler continued to take advantage of the branch and jump
-         * that bracketed the body. But given the SRC_WHILE note, it is easy
-         * to support the more efficient scheme.
-         */
-        PushStatement(bce, &stmtInfo, STMT_WHILE_LOOP, top);
-        noteIndex = NewSrcNote(cx, bce, SRC_WHILE);
-        if (noteIndex < 0)
-            return JS_FALSE;
-        jmp = EmitJump(cx, bce, JSOP_GOTO, 0);
-        if (jmp < 0)
-            return JS_FALSE;
-        noteIndex2 = NewSrcNote(cx, bce, SRC_LOOPHEAD);
-        if (noteIndex2 < 0)
-            return JS_FALSE;
-        top = EmitTraceOp(cx, bce, pn->pn_right);
-        if (top < 0)
-            return JS_FALSE;
-        if (!EmitTree(cx, bce, pn->pn_right))
-            return JS_FALSE;
-        CHECK_AND_SET_JUMP_OFFSET_AT(cx, bce, jmp);
-        if (!EmitTree(cx, bce, pn->pn_left))
-            return JS_FALSE;
-        beq = EmitJump(cx, bce, JSOP_IFNE, top - bce->offset());
-        if (beq < 0)
-            return JS_FALSE;
-        /*
-         * Be careful: We must set noteIndex2 before noteIndex in case the noteIndex
-         * note gets bigger.
-         */
-        if (!SetSrcNoteOffset(cx, bce, noteIndex2, 0, beq - top))
-            return JS_FALSE;
-        if (!SetSrcNoteOffset(cx, bce, noteIndex, 0, beq - jmp))
-            return JS_FALSE;
-        ok = PopStatementBCE(cx, bce);
+        ok = EmitWhile(cx, bce, pn, top);
         break;
 
       case PNK_DOWHILE: