Bug 203664 – codeBlock->expressionRangeForBytecodeIndex() returns wrong range for op_rshift and op_lshift

• Status: RESOLVED
• Resolution: CONFIGURATION CHANGED
• Component: JavaScriptCore

[Tuomas Karkkainen]

Created attachment 382430 [details]
repro case

for the JavaScript:

> function bar() {}
> 
> function foo() {
>   let z = 0;
>   z >>= 0;
>   z <<= 0;
>   bar();
>   for (let i=0; i<100; i++) {}
> }
> 
> foo();

the bytecode is:

> foo#DbrI6W:[0x1119a0140->0x1119c7c00, NoneFunctionCall, 64]: 19 instructions (0 16-bit instructions, 0 32-bit instructions, 5 instructions with metadata); 172 bytes (108 metadata bytes); 1 parameter(s); 14 callee register(s); 6 variable(s); scope at loc4
> [   0] enter
> [   1] get_scope          loc4
> [   3] mov                loc5, loc4
> [   6] check_traps
> [   7] mov                loc6, <JSValue()>(const0)
> [  10] mov                loc6, Int32: 0(const1)
> [  13] rshift             loc6, loc6, Int32: 0(const1)
> [  18] lshift             loc6, loc6, Int32: 0(const1)
> [  23] resolve_scope      loc8, loc4, 0, GlobalProperty, 0
> [  30] get_from_scope     loc7, loc8, 0, 2048<ThrowIfNotFound|GlobalProperty|NotInitialization>, 0, 0
> [  38] call               loc7, loc7, 1, 14
> [  44] mov                loc7, <JSValue()>(const0)
> [  47] mov                loc7, Int32: 0(const1)
> [  50] jnless             loc7, Int32: 100(const2), 12(->62)
> [  54] loop_hint
> [  55] check_traps
> [  56] inc                loc7
> [  58] jless              loc7, Int32: 100(const2), -4(->54)
> [  62] ret                Undefined(const3)
> 
> Identifiers:
>   id0 = bar
> 
> Constants:
>    k0 = <JSValue()>
>    k1 = Int32: 0: in source as integer
>    k2 = Int32: 100: in source as integer
>    k3 = Undefined

output of codeBlock->unlinkedCodeBlock()->dumpExpressionRangeInfo() is:

> UnlinkedCodeBlock 0x111998000 expressionRangeInfo[4] {
>   [0] pc 23 @ line 4 col 5 : op_resolve_scope
>   [1] pc 38 @ line 4 col 5 : op_call
>   [2] pc 50 @ line 5 col 16 : op_jnless
>   [3] pc 58 @ line 5 col 16 : op_jless
> }

codeBlock->expressionRangeForBytecodeIndex() returns:

> #13 op_rshift divot: 76 startOffset: 3 endOffset: 0 source: 'bar'
> #18 op_lshift divot: 76 startOffset: 3 endOffset: 0 source: 'bar'

afaik correct source should be:

> #13: "z >>= 0"
> #18: "z <<= 0"

for the non-assignment op_lshift and op_rshift codeBlock->expressionRangeForBytecodeIndex() points to a zero length string at the beginning of the expression.

[Yusuke Suzuki]

These bytecodes no longer have ValueProfile.