> On Jun 22, 2021, at 9:15 AM, Richard Biener <rguent...@suse.de> wrote: > > On Tue, 22 Jun 2021, Qing Zhao wrote: > >> >> >>> On Jun 22, 2021, at 9:00 AM, Richard Biener <rguent...@suse.de> wrote: >>> >>> On Tue, 22 Jun 2021, Qing Zhao wrote: >>> >>>> So, I am wondering why not still keep my current implementation on >>>> assign different patterns for different types? >>>> >>>> This major issue with this design is the code size and runtime overhead, >>>> but for debugging purpose, those are not that important, right? And we >>>> can add some optimization later to improve the code size and runtime >>>> overhead. >>>> >>>> Otherwise, if we only use one pattern for all the types in this initial >>>> version, later we still might need change it. >>>> >>>> How do you think? >>> >>> No, let's not re-open that discussion. As said we can look to support >>> multi-byte pattern if that has a chance to improve things but only >>> as followup. >> >> I am fine with this. >> >> However, we need to decide whether we will use one-byte repeatable pattern, >> or multiple-byte repeatable pattern now, >> Since the implementation will be different. If using one-byte, the >> implementation will be the simplest, we can use memset for all >> VLA, non-vla, zero-init, or pattern-init consistently. >> >> However, if we choose multiple-byte pattern, then the implementation will be >> different, we cannot use memset for pattern-init, and >> The implemenation for VLA pattern-init also is different. > > As said, we can do this as followup. For now get the easiest thing > working - one-byte patterns via memset.
Okay. I will work on this. > There's enough bits in the > patch that will likely need followup fixes (the .DEFERED_INIT stuff), Do you mean your previous suggestion to merge the handling of VLA to non-VLA during gimplification phase? I have done with this change locally. > actual code gneration of the init is separate enough we can deal with > it later. Also IMHO not all targets necessarily need to behave the > same there. Then, shall we make the code generation part a target hook now? Or do this later? Qing > > Richard. > >> Qing >>> >>> Thanks, >>> Richard. >>> >>>> Qing >>>> >>>> On Jun 22, 2021, at 3:59 AM, Richard Biener >>>> <rguent...@suse.de<mailto:rguent...@suse.de>> wrote: >>>> >>>> On Tue, 22 Jun 2021, Richard Sandiford wrote: >>>> >>>> Kees Cook <keesc...@chromium.org<mailto:keesc...@chromium.org>> writes: >>>> On Mon, Jun 21, 2021 at 03:39:45PM +0000, Qing Zhao wrote: >>>> So, if “pattern value” is “0xFFFFFFFFFFFFFFFF”, then it’s a valid >>>> canonical virtual memory address. However, for most OS, >>>> “0xFFFFFFFFFFFFFFFF” should be not in user space. >>>> >>>> My question is, is “0xFFFFFFFFFFFFFFFFF” good for pointer? Or >>>> “0xAAAAAAAAAAAAAAAA” better? >>>> >>>> I think 0xFF repeating is fine for this version. Everything else is a >>>> "nice to have" for the pattern-init, IMO. :) >>>> >>>> Sorry to be awkward, but 0xFF seems worse than 0xAA to me. >>>> >>>> For integer types, all values are valid representations, and we're >>>> relying on the pattern being “obviously” wrong in context. 0xAAAA… >>>> is unlikely to be a correct integer but 0xFFFF… would instead be a >>>> “nice” -1. It would be difficult to tell in a debugger that a -1 >>>> came from pattern init rather than a deliberate choice. >>>> >>>> I agree that, all other things being equal, it would be nice to use NaNs >>>> for floats. But relying on wrong numerical values for floats doesn't >>>> seem worse than doing that for integers. >>>> >>>> 0xAA… for float is (if I've got this right) -3.0316488252093987e-13, >>>> which admittedly doesn't stand out as wrong. But I'm not sure we >>>> should sacrifice integer debugging for float debugging here. >>>> >>>> We can always expose the actual value as --param. Now, I think >>>> we'd need a two-byte pattern to reliably produce NaNs anyway, >>>> so with floats taken out of the picture the focus should be on >>>> pointers where IMHO val & 1 and val & 15 would be nice to have. >>>> So sth like 0xf7 would work for those. With a two-byte pattern >>>> we could use 0xffef or 0x7fef. >>>> >>>> Anyway, it's probably down to priorities of the project involved >>>> (debugging FP stuff or integer stuff). >>>> >>>> Richard. >>>> >>>> >>> >>> -- >>> Richard Biener <rguent...@suse.de> >>> SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg, >>> Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg) >> >> > > -- > Richard Biener <rguent...@suse.de> > SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg, > Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)
