On 23/06/2014 15:02, Aaron Ballman wrote:
On Sun, Jun 22, 2014 at 10:09 PM, Alp Toker <[email protected]> wrote:
On 23/06/2014 04:30, Saleem Abdulrasool wrote:
On Sun, Jun 22, 2014 at 4:15 PM, Alp Toker <[email protected]
<mailto:[email protected]>> wrote:
On 23/06/2014 01:53, Saleem Abdulrasool wrote:
On Sat, Jun 21, 2014 at 11:32 AM, Alp Toker <[email protected]
<mailto:[email protected]> <mailto:[email protected]
<mailto:[email protected]>>> wrote:
Late to the party with review but I have some points of
review..
On 21/06/2014 01:58, Saleem Abdulrasool wrote:
Author: compnerd
Date: Fri Jun 20 17:58:35 2014
New Revision: 211420
URL:
http://llvm.org/viewvc/llvm-project?rev=211420&view=rev
Log:
Driver: enhance MSC version compatibility
The version information for Visual Studio is spread over
multiple variables.
The newer Windows SDK has started making use of some
of the
extended versioning
variables that were previously undefined. Enhance our
compatibility definitions
for these cases.
_MSC_VER is defined to be the Major * 100 + Minor.
_MSC_FULL_VER is defined to
be Major * 10000000 + Minor * 100000 + Build. And
_MSC_BUILD
is the build
revision of the compiler.
Extend the -fmsc-version option in a compatible
manner. If
the value is the
previous form of MMmm, then we assume that the build
number is
0. Otherwise, a
specific build number may be passed by using the form
MMmmbbbbb.
We shouldn't overload the semantics of compiler options
like this,
because doing so:
I did this based on review feedback.
Hi Saleem,
I read the review thread and don't see any mention of
canonicalisation issues, or the bug where 17.0 and 17 are
mishandled. The review was mostly about coding style.
http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20140616/108136.html
I have a slight preference for it, but its not a strong
opinion. I would rather Reid and Aaron chime in and we decide
on the path we wish to take before I spend effort to try to
change the behaviour added here.
I wrote a detailed point-by-point review about how this doesn't
fit in with the design of our driver or expected usage -- could
you be more specific?
I was referring to the dot-separated value.
Accepting a dotted version is fine. Overloading the existing -fmcs-version=
option is the problem..
Given that this is meant to be backwards compatible, I'm not certain I
understand what the problem actually is. If the option isn't backwards
compatible, that's simply a bug we should fix.
* Makes configure-time feature detection harder ("but the
option
exists, why doesn't it accept my input?")
This seems like it is a pre-existing problem, not something specific to
this change.
Nope, definitely specific to this change.
Can you elaborate?
* Confuses argument canonicalization routines in external tools
like ccache, potentially requiring special handling to be
duplicated in each external project.
Can you provide some concrete example of this please? Im afraid I dont
see how that would happen.
External tools need to parse and grok driver arguments. Supporting two
syntaxes in a single option requires custom handling to be developed in each
tool -- there are very few other options like yours in the clang driver.
Where they exist, it's done out of necessity to support GCC bugs.
Your feature could easily be implemented as a second flag at no cost, and
that seems to be the obvious way to go. Is there a problem with actually
doing that?
Then users (whose experience I care about *far* more than external
tools vendors) have two options which serve the same purpose, and
creates some confusion as to which one should be used, what situations
they should use them in, and why. Having a single option presents a
better user experience, IMO.
This is interesting. To me, it's as clear as day that accepting two
incompatible version formats in a single option flag is bad for users
and tools. It's also unprecedented -- we've not done this before with
any driver option. There are many options that have multiple forms for
different inputs syntax.
Why is this flag so special that we need to break all the rules and
introduce command-line parsing disambiguations?
It's not at all obvious to a user that '17.0' or '17.0.0' defines macros
as version 17 while '17' defines macros as version 0.0.0.17. Predicating
on presence of a '.' is going to look like a bug to any user who
encounters it.
Another point, clang 3.4 and earlier driver will actively diagnose the
new flag and let the user know:
New option flag with the 3.4 driver:
$ clang -fmsc-full-version=15.00.20706.01 -###
clang version 3.5.0
Target: x86_64-apple-darwin13.2.0
Thread model: posix
Whereas the overloaded option flag produces an error to let the user know:
$ clang -fmsc-version=15.00.20706.01 -###
clang-3.4: error: unknown argument: '-fmsc-full-version=15.00.20706.01'
clang version 3.5.0
Target: x86_64-apple-darwin13.2.0
Thread model: posix
And the former is just more work for configure scripts to detect whether
the syntax is supported. They have to run a real compilation to
determine if there's an error for no good reason at all.
A flag accepting a specific and long version number like
"15.00.20706.01" needs to have really clear semantics and documentation.
The obvious way to achieve that is to have two flags -- one that accepts
the legacy encoded version number, and a new one that accepts the
user-friendly format.
Also have we confirmed that the Visual Studio variables actually provide
a version number in this format (I think so, but we should dogfood it).
Right now we have to pre-process the value on the LLVM side before
feeding it into clang and that's the primary consumer of this flag.
Alp.
* Breaks representation in IDE integration property pages: we'd
like to use an integer mask for the numeric version form,
and a
dotted masked input selector in the GUI for fields like this.
Overloading the syntax as in your patch means it can only be
presented as an untyped string field.
Not sure what you are referring to here. What IDE are you talking about?
The entire point of the compatibility format is that the old format
continues. You can provide it as an integral value.
* Semantically inconsistent:
-msc-version=17.0.0:
#define _MSC_VER 1700
-msc-version=17.0:
#define _MSC_VER 1700
-msc-version=17:
#define _MSC_VER 17
I didnt think that we supported this previously, but, if it is simply a
matter of handling this case as well, I am more than happy to accommodate
that.
I don't see how you could accommodate that without adding more
disambiguations, checking for '.' characters or testing the input length, or
perhaps detecting if it's a very large or small number.
We already check for the '.' character in this patch... extending that
hardly seems problematic?
The base case where the input is integral will always conflict -- you have
no way to guess which one the user intended.
The quirks are already problematic and adding more isn't the solution here:
This could easily be made into two distinct options, and we'll then be able
to clearly document the newly-added option so users know straight away if
it's supported in their version of clang.
I'm weakly opposed to adding a second flag here, because I'm not
convinced one is required, or desirable.
~Aaron
--
http://www.nuanti.com
the browser experts
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