On Wed, Jul 18, 2012 at 11:19 AM, Chandler Carruth <[email protected]>wrote:
> On Wed, Jul 18, 2012 at 11:12 AM, John McCall <[email protected]> wrote: > >> On Jul 18, 2012, at 2:28 AM, Chandler Carruth wrote: >> >> On Tue, Jul 17, 2012 at 11:47 PM, Richard Smith <[email protected]>wrote: >> >>> On Tue, Jul 17, 2012 at 11:26 PM, Chandler Carruth <[email protected] >>> > wrote: >>>> >>>> I find the definition of APInt's operator== deeply troubling. Why >>>> *assert* if the bit widths aren't equal? That doesn't make a lot of sense >>>> to me. The function that it calls to actually implement it turns around and >>>> considers mismatched bitwdiths to cause *inequality*. >>>> >>>> However it seems that there is a very simple definition of equality we >>>> could use instead: zero-extended equality for APInt, and sign-extended >>>> equality for APSInt. I wonder if there would be general support for making >>>> APInt::operator== and APSInt::operator== work in this more rational >>>> model... >>>> >>> >>> APInt has no knowledge of whether its high bit is a sign bit, so always >>> zero-extending will be wrong in the case where it is in fact a sign bit. >>> APSInt does know this, so if we want to support heterogenous comparisons, >>> we should sign-extend if the APSInt is signed, and zero-extend if it is >>> unsigned. Heterogenous comparison on APInt is fundamentally unsafe, so >>> asserting there seems reasonable to me. >>> >> >> Well, Nick's comment may obviate the extension question, which leaves us >> with a simpler problem of comparing the same sizes for equality or >> inequality. I don't actually see any problems comparing same-sized APInts >> and APSInts for equality or inequality as-if they were both APInts. Given >> two APSInts, I think that the signedness should participate in the equality >> test though... >> >> >> It seems silly for APInt to treat bitwidth inequality as an illegal >> operation but APSInt to treat it as a semantic difference. APInt's >> assertions *do* find bugs; I would much rather extend those to APSInt than >> have it forge a new contract. >> > > I never intended to suggest inconsistency between the two. I just didn't > understand the motivation for the assertion even at the APInt layer. Nick > provided that though, which was all I needed. =] > > New patch. Switched int parameters to int64_t. APSInt::operator!= now refers to APSInt::operator==
APSInt-llvm2.patch
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