423660 - create a literal pool instead of inlining each literal separately

Status: RESOLVED FIXED

(Tamarin Graveyard :: Tracing Virtual Machine, defect, P2)

Description

[Edwin Smith]

each time arm or thumb codes needs to insert inline data, you will get:

B target
data
padding
target: ...

this is a constant pool of one, we use PC relative addressing to reach it.  we can do much better.

Thumb:
- only positive offsets from PC are supported.  
- +1K range

Arm:
- positive & negative offsets supported.  +/-4K range is supported.

TC's prototype Arm support puts a constant pool at the bottom of each 4K page as it generates code in a forward pass.  when the forward growing code meets the backwards growing cpool, we start a new page.  with backwards generation and backwards indexing to the cpool, this will also work on ARM, just doing it upside down.

Comment 1

[Rob Winchell]

Attachment: Initial implementation for literal pools on ARM/Thumb

On ARM, values are inserted at top of page and pool grows downward as code grows upward.

On Thumb, pools are interleaved with code. Size of pool is controlled by compile-time constant (currently 16).

Comment 2

[Rob Winchell]

Attachment: Updated patch

Updated patch with platform specific implementation separated out.

Comment 3

[Edwin Smith]

* what's with isB22() being commented out in CALL() for Thumb?

* is the math in arm underrunProtect() right?

  on arm, i think we need to check samePage(nIns-u, nIns-1)

  arm:   u = (intptr_t)_nIns - 8;
  thumb: u = (intptr_t)_nIns - 2;

  should arm be nIns-4?  

Comment 4

[Edwin Smith]

Comment on attachment 320720 [details] [diff] [review]
Updated patch

good to go if you can double check that underrunProtect() math

Comment 5

[Rick Reitmaier]

might be nice for pageAlloc() to return a Page* then you can avoid the +1 math to get around the next pointer and simply do ->nIns.

Also, it might be worthwhile to remember what constants are on the page, so that we can re-use them, that is assuming we are imm folding at the instruction level.  If we aren't then we won't need to.