[lldb-dev] GSoC 2018 Student Applications
Dear Prospective GSoC Students, The student applications website is currently open and there are still 4 days before the deadline. While you can submit your proposals directly there we strongly suggest you to submit, refine and discuss your proposals via the corresponding mailing lists. The "Open Projects" page at http://llvm.org/OpenProjects.html has some ideas for may-be projects. However, you could also submit your own project provided that the proposal is strong enough. Please do not forget to indicate your current familiarity with LLVM and whether you already contributed to any of its subprojects. Have luck! -- With best regards, Anton Korobeynikov Department of Statistical Modelling, Saint Petersburg State University ___ lldb-dev mailing list lldb-dev@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev
[lldb-dev] LLVM Social - Paris: March 27th, 2018
The next LLVM social in Paris will happen on March 27th, 2018. Everyone interested in LLVM, Clang, lldb, Polly, lld, ... is invited to join. Event details, including registration (free but mandatory) at http://www.meetup.com/LLVM-Clang-social For this meetup, we will have a presentation from Gergö Barany about "Finding Missed Optimizations in LLVM". Looking forward to meet you ! -- Arnaud de Grandmaison, Duncan Sands, Sylvestre Ledru ___ lldb-dev mailing list lldb-dev@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev
[lldb-dev] intended semantics of Scalar
While trying to use Scalar in my code, I've found some oddities.
In particular, binary promotion does a bitwise reinterpretation of an
integer when promoting to a floating point type.
This was easy enough to fix, for most cases, but it caused more
questions:
* What are the intended semantics of operations like Float and Double?
For example, I tried to write a unit test for this but I am not sure
if it is correct:
int a2 = 23;
Scalar a2_scalar(a2);
ASSERT_EQ((float)a2, a2_scalar.Float());
ASSERT_EQ((double)a2, a2_scalar.Double());
The current code here also does bitwise reinterpretation.
This comment appears in Scalar.h but I did not find it much clearer:
//--
// Returns a casted value of the current contained data without
// modifying the current value. FAIL_VALUE will be returned if the type
// of the value is void or invalid.
//--
* What is the intended difference between the Cast and Promote methods?
These don't have comments.
* Are the 128- and 256-bit integers expected to participate in binary
promotion the same way that other ints do? If so then it seems to me
that other parts of the code are also incorrect, for example in
PromoteToMaxType:
if (lhs_type > rhs_type) { [...]
This will cause Scalar to attempt to promote floating point types to
these wide integer types; but that doesn't seem correct to me. There
may be more such problems, I did not check exhaustively.
thanks,
Tom
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Re: [lldb-dev] intended semantics of Scalar
> On Mar 23, 2018, at 2:27 PM, Tom Tromey via lldb-dev
> wrote:
>
> While trying to use Scalar in my code, I've found some oddities.
>
> In particular, binary promotion does a bitwise reinterpretation of an
> integer when promoting to a floating point type.
>
> This was easy enough to fix, for most cases, but it caused more
> questions:
>
> * What are the intended semantics of operations like Float and Double?
> For example, I tried to write a unit test for this but I am not sure
> if it is correct:
>
> int a2 = 23;
> Scalar a2_scalar(a2);
> ASSERT_EQ((float)a2, a2_scalar.Float());
> ASSERT_EQ((double)a2, a2_scalar.Double());
>
> The current code here also does bitwise reinterpretation.
>
> This comment appears in Scalar.h but I did not find it much clearer:
>
> //--
> // Returns a casted value of the current contained data without
> // modifying the current value. FAIL_VALUE will be returned if the type
> // of the value is void or invalid.
> //--
>
> * What is the intended difference between the Cast and Promote methods?
> These don't have comments.
>
> * Are the 128- and 256-bit integers expected to participate in binary
> promotion the same way that other ints do? If so then it seems to me
> that other parts of the code are also incorrect, for example in
> PromoteToMaxType:
>
> if (lhs_type > rhs_type) { [...]
>
> This will cause Scalar to attempt to promote floating point types to
> these wide integer types; but that doesn't seem correct to me. There
> may be more such problems, I did not check exhaustively.
It was initially intended to mimic the C promotion rules when doing
expressions. The scalar values are used in a lot of place, but most importantly
in the DWARF expression parser. Can't remember if the AST expression parser
uses them as well when expressions are simple enough.
Basically we want the class to behave like C/C++ expressions, when to do
something like:
auto result = 22 + 3.2
we want "result" to match if we used Scalar objects.
Promote is used to promote a type during an expression. In the above example
"22" should be promoted to a matching float type as "22.0". If your expression
was:
int result = 22 + 3.2
I would think we would use "Cast" to chase the "22.0" to 22. There don't seem
to be any callers (at least that is what Xcode says) to the Scalar::Cast(...)
function, so it could be removed.
It used to be that Scalar just contained integers up to uint64_t, but later
this code was converted to use llvm::APIInt and llvm::APFloat classes. Not sure
if that is when bugs crept it. But that should give us the ability to use any
size integers IIRC.
Basically, I would be happy if the Scalar class can automatically do what C/C++
expression would do with similar types. That should make it easy to find errors
and to unit test as the test can be:
auto result = 22 + 3.2;
Scalar a(22);
Scalar b(3.2);
c = a + b;
verify(c == result);
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