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

David Majnemer david.majnemer at gmail.com
Mon Sep 1 14:16:25 PDT 2014

On Mon, Sep 1, 2014 at 2:09 PM, Renato Golin <renato.golin at linaro.org>

> 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?

I've figured out the problem, a fix is on it's way.

The problem wasn't the math behind the transform; there was a bug in the
way I wrote the pattern matching.

> cheers,
> --renato
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