js/src/jit-test/tests/basic/bigLoadStoreDisp.js

Wed, 31 Dec 2014 06:09:35 +0100

author
Michael Schloh von Bennewitz <michael@schloh.com>
date
Wed, 31 Dec 2014 06:09:35 +0100
changeset 0
6474c204b198
permissions
-rw-r--r--

Cloned upstream origin tor-browser at tor-browser-31.3.0esr-4.5-1-build1
revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.

     1 // In Nanojit, loads and stores have a maximum displacement of 16-bits.  Any
     2 // displacements larger than that should be split off into a separate
     3 // instruction that adds the displacement to the base pointer.  This
     4 // program tests if this is done correctly.
     5 //
     6 // x.y ends up having a dslot offset of 79988, because of the 20000 array
     7 // elements before it.  If Nanojit incorrectly stores this offset into a
     8 // 16-bit value it will truncate to 14452 (because 79988 - 65536 == 14452).
     9 // This means that the increments in the second loop will be done to one of
    10 // the array elements instead of x.y.  And so x.y's final value will be
    11 // (99 + 8) instead of 1099.
    12 //
    13 // Note that setting x.y to 99 and checking its value at the end will
    14 // access the correct location because those lines are interpreted.  Phew.
    16 var x = {}
    17 for (var i = 0; i < 20000; i++)
    18     x[i] = 0;
    19 x.y = 99;            // not traced, correctly accessed
    21 for (var i = 0; i < 1000; ++i) {
    22     x.y++;           // traced, will access an array elem if disp was truncated
    23 }
    24 assertEq(x.y, 1099); // not traced, correctly accessed

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