Change the way the JIT renumbers byte code temps #6232
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boingoing
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Sep 10, 2019
| @@ -45,7 +45,7 @@ EXDEF2 (BRLONG, BrLong, OP_Br) | |||
| #endif | |||
| DEF3 (CUSTOM, StartCall, OP_StartCall, StartCall) | |||
| DEF2 (NOP, Nop, Empty) | |||
| DEF2_WMS(NOP, Unused, Reg1) | |||
| // DEF2_WMS(NOP, Unused, Reg1) | |||
boingoing
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Sep 10, 2019
chakrabot
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Sep 12, 2019
Merge pull request #6232 from pleath:no-unused The JIT currently does not renumber byte code temps in boolean-expression-like cases that have the form: Brm $L1 Rm = op1 ... Br $L2 $L1: Rm = op2 ... $L2: ... = op3 Rm This is hard to maintain, because it relies on conscientious use of the Unused op in byte code where a def of a register is not followed by a use, but we still want to renumber the register at the next use. Failure to emit Unused results in silent failure to renumber, which in turn results in suboptimal jitted code. This change deletes Unused, adds several byte codes of the form op_ReuseLoc, and causes the JIT to renumber lifetimes at each def unless the op_ReuseLoc is emitted. Failure to emit op_ReuseLoc will produce incorrect code that is detectable by the JIT (i.e., temps not defined on all paths). The biggest change is to the family of byte code patterns we emit to handle dynamic binding cases. These are restructured to limit the kinds of op_ReuseLoc ops we need to define.
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The JIT currently does not renumber byte code temps in boolean-expression-like cases that have the form:
Brm $L1
Rm = op1 ...
Br $L2
$L1:
Rm = op2 ...
$L2:
... = op3 Rm
This is hard to maintain, because it relies on conscientious use of the Unused op in byte code where a def of a register is not followed by a use, but we still want to renumber the register at the next use. Failure to emit Unused results in silent failure to renumber, which in turn results in suboptimal jitted code. This change deletes Unused, adds several byte codes of the form op_ReuseLoc, and causes the JIT to renumber lifetimes at each def unless the op_ReuseLoc is emitted. Failure to emit op_ReuseLoc will produce incorrect code that is detectable by the JIT (i.e., temps not defined on all paths). The biggest change is to the family of byte code patterns we emit to handle dynamic binding cases. These are restructured to limit the kinds of op_ReuseLoc ops we need to define.