On 01/06/2017 07:15:47, Richard Sandiford wrote: > Prakhar Bahuguna <prakhar.bahug...@arm.com> writes: > > On 31/05/2017 14:11:43, Richard Sandiford wrote: > >> Prakhar Bahuguna <prakhar.bahug...@arm.com> writes: > >> > On 31/05/2017 09:19:40, Richard Sandiford wrote: > >> >> const_ints are supposed to be stored in sign-extended form, so a 32-bit > >> >> integer with the MSB set should be 0xffffffff80000000|x instead of > >> >> 0x80000000|x. It's a bug if you have one where that isn't true. > >> >> > >> >> In the patch it looks like this could come from: > >> >> ...these two splits, where the GEN_INTs should probably be: > >> >> > >> >> gen_int_mode (..., SImode); > >> >> > >> >> instead. > >> > > >> > Hi Richard, thanks for the tip. Is there a test case that could produce > >> > an > >> > incorrect result? I've attempted to create one using negative doubles and > >> > floats but haven't succeeded. > >> > >> Just to check, are you testing with --enable-checking=yes,rtl? > >> > >> When the values you tried were split, did you get the sign-extended form > >> or the zero-extended form? > >> > >> Thanks, > >> Richard > > > > I've now rebuilt with --enable-checking=yes,rtl and it appears that the > > split > > values are being correctly sign-extended in the rtl and appear correctly in > > the > > assembly. > > > > However, if you believe it is safer to use gen_int_mode(), I'll respin the > > patch accordingly. > > Yeah, I think it would be safer. But if they were already correctly > sign-extended, then what did you mean by: > > Also the pattern for splitting 32-bit immediates had to be changed, it > was not accepting unsigned 32-bit unsigned integers with the MSB > set. I believe const_int_operand expects the mode of the operand to be > set to VOIDmode and not SImode. I have only changed it in the patterns > that were affecting this code, though I suggest looking into changing > it in the rest of the ARM backend. > > Thanks, > Richard
This part of the patch was written by Andre. After checking with him, it seems that some of the confusion arises from the comment on real_to_target() which states "There are always 32 bits in each long, no matter the size of the host long". While this may imply the value is zero-extended on hosts with wider longs, it seems like the value is always correctly sign-extended and thus gen_int_mode() should be unnecessary. As for why VOIDmode is used with the values casted to int, there is a reason for why it is done this way to get it working but this has been long-forgotten. I only have the code and this message to rely on. -- Prakhar Bahuguna
