On Sun, Oct 28, 2018 at 01:39:16PM -0400, Paul Koning wrote: > I was reviewing some back end code that handles integer values of various > sizes, and got confused reading about CONST_INT and CONST_DOUBLE. > > It's pretty clear that CONST_DOUBLE is used for values bigger than > HOST_WIDE_INT. But the description of INTVAL is contradictory. In some > places, it states that its type is HOST_WIDE_INT; in others it says that it > it "int". For example, in section 17.6 of the internals manual: > > Be careful when doing this, because the result of INTVAL is an integer on the > host machine. If the host machine has more bits in an int than the target > machine has in the mode in which the constant will be used, then some of the > bits you get from INTVAL will be superfluous.
It is a HOST_WIDE_INT. The section (please mention the title btw., the section numbers change over time: this is "C Statements for Assembler Output") isn't very clear, and it was written when HOST_WIDE_INT could still be 32 bit (nowadays it is always 64 bits). > A related problem is that it isn't clearly stated what the properties of > HOST_WIDE_INT are. Judging by hwint.h, it is always specifically a 64 bit > integer. If that is intended to be the case, it would be good for that to be > documented. Alternatively, if the intent is that it is at least 64 bits but > might be bigger, that should be stated. As it stands, I have some code I > need to repair because it picks apart integer constants from INTVAL in a way > that's incorrect if a 64-bit value is passed. It is always exactly 64 bits. HOST_WIDE_INT values are always sign-extended to the type it is meant as (so 0x80 is expressed as 0xffffffffffffff80 for a QImode value, i.e. -0x80, but it is just 0x80 for a larger mode value). Segher
