[llvm-commits] [VIRUS PM SCAN ERROR] RFC: Disable Constant Island Pass for Native Client (demo CL's)

[Jason Kim]

Hello everyone

Please find enclosed a sequence of three patches, for the goal of disabling
constant island pass, which is required for Native Client.

These patches are based off of r147863, so its pretty far back, but I am
posting these mainly to get feedback on certain glitches in ARM/thumb2
tablegen that we ran into when we tried to port our local mods (which
operate in ARM mode perfectly well) to Thumb2 mode.

These patches are by no means "functional", but I deem it to be both small
enough, AND substantial enough to show our intention/plan for disabling
Constant Island Pass - and most importantly, get feedback from the
ARM/Thumb2 tablegen experts on exactly what the right way to do this is:
These are distilled subsets of our current set of local mods, and are meant
as 'for review only' (for now at least). Eventually, we would like to
upstream as much of these as possible, but that requires a lot of splitting
of our local mods into digestible chunks.
Please consider these patches as a first in a potentially long sequence of
hopefully coherent split of NaCl localmods for upstreaming purposes.

The most questionable bits are in  the second patch, where  the Thumb2 ISEL
match to properly lower a constant pool address to a pc relative movw/movt
never happens.
Matter of fact, the pci pattern in the multiclass T2I_ld seems to be the
culprit.  Currently, in our local repository, what we do is to generate a
NaCl version of the pseudo for the *pci expansion and custom expand them to
the required movw/movt.

This methodology, although functional, seems somehow 'dirty' and we were
wondering if there is a better way to do this. Certainly, in ARM codegen,
such hackery was NOT necessary.

The patches themselves contain comments which will hopefully explain some
more of the details.

Thank you

-Jason
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