Add VIEW_CONVERT_EXPR to operand_equal_p
Eric Botcazou
ebotcazou@adacore.com
Sat Oct 31 17:39:00 GMT 2015
> Lets go with this patch and hopefully stabilize the tree. I don't think the
> vector conversions represent an important case.
Unfortunately the patch introduces GIMPLE checking failures in Ada so it will
need to be completed/improved. But let's postpone it because we have another
class of GIMPLE checking failures introduced by the useless_type_conversion_p
change itself:
c37213j.adb:21:05: warning: variable "X" is read but never assigned
c37213j.adb: In function 'C37213J.PROC.CONSTPROP':
c37213j.adb:41:4: error: invalid conversion in gimple call
struct c37213j__proc__value___PAD
struct c37213j__proc__value___PAD
# .MEM_38 = VDEF <.MEM_37>
MEM[(struct c37213j__proc__value___PAD *)R.12_25] = c37213j.proc.value ();
[static-chain: &FRAME.39] [return slot optimization]
and:
eric@polaris:~/build/gcc/native> ~/install/gnat-head/bin/gcc -S c37213j.adb -
O2
c37213j.adb:21:05: warning: variable "X" is read but never assigned
c37213j.adb: In function 'C37213J.PROC.VALUE':
c37213j.adb:26:5: error: invalid conversion in return statement
struct c37213j__proc__value___PAD
struct c37213j__proc__value___PAD
# VUSE <.MEM_11>
return _9(D);
What happens here is that GIMPLE statements are remapped through cloning and
we have a variably-modified type returned by a nested function, so the type of
the LHS of a GIMPLE_CALL or that of the RHS of a GIMPLE_RETURN is remapped but
of course not the return type of the function. This used to be OK because
remapping is done by means of copy_node and preserves TYPE_CANONICAL, so the
conversion between remapped and original type was deemed useless; now the
TYPE_CANONICAL check is gone so the conversion is not useless anymore...
I don't think that we want to introduce an artificial VCE to fix this so we
probably need a couple of kludges in the GIMPLE verifier instead.
In any case, the more I look into the fallout of the useless_type_conversion_p
change, the more I find it ill-advised. We used to have a solid type system
in the middle-end by means of the predicate and now we have cases for which it
ought to return false and returns true (e.g. non-structurally equivalent types
with different calling conventions) and cases for which it can return true and
returns false (remapped types or types deemed equivalent by the languages).
I don't really know what it was made for, but there must be a better way...
* gnat.dg/discr45.adb: New test.
--
Eric Botcazou
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