| Message ID | alpine.DEB.2.02.1711221809380.11945@stedding.saclay.inria.fr |
|---|---|
| State | New |
| Headers | show |
| Series | Simplify ptr - 0 | expand |
On Wed, Nov 22, 2017 at 06:34:08PM +0100, Marc Glisse wrote: > Hello, > > I hadn't implemented this simplification because I think it is invalid code, > but apparently people do write it, so we might as well handle it sensibly. > This also happens to work around PR 83104 (already fixed). > > bootstrap+regtest on powerpc64le-unknown-linux-gnu. I guess we'll need to disable it for -fsanitize=pointer-subtraction once/if it makes it in, because it should be still diagnosed as invalid. > 2017-11-22 Marc Glisse <marc.glisse@inria.fr> > > * match.pd (ptr-0): New transformation. > > -- > Marc Glisse Jakub
On Wed, 22 Nov 2017, Jakub Jelinek wrote: > On Wed, Nov 22, 2017 at 06:34:08PM +0100, Marc Glisse wrote: >> Hello, >> >> I hadn't implemented this simplification because I think it is invalid code, >> but apparently people do write it, so we might as well handle it sensibly. >> This also happens to work around PR 83104 (already fixed). >> >> bootstrap+regtest on powerpc64le-unknown-linux-gnu. > > I guess we'll need to disable it for -fsanitize=pointer-subtraction > once/if it makes it in, because it should be still diagnosed as invalid. I am not sure you'll need to disable it. From what I've seen, the patch inserts a call to BUILT_IN_ASAN_POINTER_SUBTRACT before the POINTER_DIFF_EXPR is created, and I don't see why simplifying POINTER_DIFF_EXPR would affect that call. But then again, I don't know how the sanitizers work, so I can easily misinterpret things.
On Wed, Nov 22, 2017 at 6:34 PM, Marc Glisse <marc.glisse@inria.fr> wrote: > Hello, > > I hadn't implemented this simplification because I think it is invalid code, > but apparently people do write it, so we might as well handle it sensibly. > This also happens to work around PR 83104 (already fixed). > > bootstrap+regtest on powerpc64le-unknown-linux-gnu. Ok. What about 0 - ptr? (ok, that's even more weird) Richard. > 2017-11-22 Marc Glisse <marc.glisse@inria.fr> > > * match.pd (ptr-0): New transformation. > > -- > Marc Glisse
On Thu, 23 Nov 2017, Richard Biener wrote: > On Wed, Nov 22, 2017 at 6:34 PM, Marc Glisse <marc.glisse@inria.fr> wrote: >> Hello, >> >> I hadn't implemented this simplification because I think it is invalid code, >> but apparently people do write it, so we might as well handle it sensibly. >> This also happens to work around PR 83104 (already fixed). >> >> bootstrap+regtest on powerpc64le-unknown-linux-gnu. > > Ok. > > What about 0 - ptr? (ok, that's even more weird) I thought about it, but it seemed less likely (I can imagine the idiom ptr-0 being used to let the compiler guess the right type). I'll add 0-ptr if you think that may be useful.
On Thu, 23 Nov 2017, Richard Biener wrote:
> What about 0 - ptr? (ok, that's even more weird)
* match.pd (0-ptr): New transformation.
Regtested on gcc112.
On Fri, Nov 24, 2017 at 10:18 AM, Marc Glisse <marc.glisse@inria.fr> wrote: > On Thu, 23 Nov 2017, Richard Biener wrote: > >> What about 0 - ptr? (ok, that's even more weird) > > > * match.pd (0-ptr): New transformation. > > Regtested on gcc112. Ok. Thanks, Richard. > -- > Marc Glisse > Index: gcc/match.pd > =================================================================== > --- gcc/match.pd (revision 255118) > +++ gcc/match.pd (working copy) > @@ -2449,23 +2449,27 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT) > (minus @0 { tem; }))))) > > /* Convert x+x into x*2. */ > (simplify > (plus @0 @0) > (if (SCALAR_FLOAT_TYPE_P (type)) > (mult @0 { build_real (type, dconst2); }) > (if (INTEGRAL_TYPE_P (type)) > (mult @0 { build_int_cst (type, 2); })))) > > +/* 0 - X -> -X. */ > (simplify > (minus integer_zerop @1) > (negate @1)) > +(simplify > + (pointer_diff integer_zerop @1) > + (negate (convert @1))) > > /* (ARG0 - ARG1) is the same as (-ARG1 + ARG0). So check whether > ARG0 is zero and X + ARG0 reduces to X, since that would mean > (-ARG1 + ARG0) reduces to -ARG1. */ > (simplify > (minus real_zerop@0 @1) > (if (fold_real_zero_addition_p (type, @0, 0)) > (negate @1))) > > /* Transform x * -1 into -x. */ >
Index: gcc/match.pd =================================================================== --- gcc/match.pd (revision 255052) +++ gcc/match.pd (working copy) @@ -95,20 +95,25 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT) (for op (plus pointer_plus minus bit_ior bit_xor) (simplify (op @0 integer_zerop) (non_lvalue @0))) /* 0 +p index -> (type)index */ (simplify (pointer_plus integer_zerop @1) (non_lvalue (convert @1))) +/* ptr - 0 -> (type)ptr */ +(simplify + (pointer_diff @0 integer_zerop) + (convert @0)) + /* See if ARG1 is zero and X + ARG1 reduces to X. Likewise if the operands are reversed. */ (simplify (plus:c @0 real_zerop@1) (if (fold_real_zero_addition_p (type, @1, 0)) (non_lvalue @0))) /* See if ARG1 is zero and X - ARG1 reduces to X. */ (simplify (minus @0 real_zerop@1)