[llvm] r216523 - InstCombine: Optimize GEP's involving ptrtoint better

[Renato Golin]

On 1 September 2014 20:14, Doug Gilmore <Doug.Gilmore at imgtec.com> wrote:
> Unfortunately it is also just in SPASS, so it probably doesn't provide much help in
> producing an isolated test case.

Shame.

On my side, the problem seems to be simplifying a read from a constant
pool or global area to an indirect register read, is that the same in
your case? There's a lot of inlining going on in that area, making it
harder to guess the pattern. What I did was to compile with the patch
in on -O2, and with the patch reverted on -O2 and compare the debug
disassembly just before the exception happens.

I don't think that's the *only* place that optimisation changed the
whole test-suite, so I believe it's just a corner case that both MIPS
and ARM have in common that probably x86 doesn't. If your problem
breaks on the same place, at least we know that's true.

Nuno,

You seem to have an idea of what could break the assumption, maybe you
can try a few cases on opt if the value of the pointer comes from a
global offset or a local constant?

cheers,
--renato