[foreign] RFR 8219822: Jextract should handle complex macro constants

Thu Feb 28 15:01:41 UTC 2019

Updated webrev:

http://cr.openjdk.java.net/~mcimadamore/panama/8219822_v4/

This sues <stdint.h> and then 'uintptr_t' instead of long, which is the 
right thing to do.

Did not notice any adverse performance issue. I also added your extra test.

Maurizio

On 28/02/2019 13:43, Maurizio Cimadamore wrote:
>
> On 28/02/2019 13:01, Jorn Vernee wrote:
>> Hi Maurizio,
>>
>> Some comments:
>>
>> * For pointers, I thought casting to (long) would truncate the value 
>> on Windows, since long is only 32 bits there, but in practice this 
>> does not seem to be a problem... Any ways, we should probably make 
>> sure that that case keeps working. Here's the test case I used:
>
> Right, I knew I was doing something dirty - Ideally we want size_t, 
> but that depends on stddef.h... I wanted to avoid extra dependencies 
> in the reparsed snippet.
>
> Interesting that it works - I'd say the clang eval API keeps the value 
> as a 64-bit value regardless of the cast...
>
> Maurizio
>
>>
>> ```
>> diff -r 8f30f51887d9 test/jdk/com/sun/tools/jextract/ConstantsTest.java
>> --- a/test/jdk/com/sun/tools/jextract/ConstantsTest.java Thu Feb 28 
>> 12:34:49 2019 +0100
>> +++ b/test/jdk/com/sun/tools/jextract/ConstantsTest.java Thu Feb 28 
>> 13:29:40 2019 +0100
>> @@ -101,7 +101,8 @@
>>                  { "CHAR_VALUE", int.class, equalsTo(104) }, 
>> //integer char constants have type int
>>                  { "MULTICHAR_VALUE", int.class, equalsTo(26728) },  
>> //integer char constants have type int
>>                  { "BOOL_VALUE", boolean.class, equalsTo(true) },
>> -                { "ZERO_PTR", Pointer.class, pointerEqualsTo(0L) }
>> +                { "ZERO_PTR", Pointer.class, pointerEqualsTo(0L) },
>> +                { "F_PTR", Pointer.class, 
>> pointerEqualsTo(0xFFFF_FFFF_FFFF_FFFFL) }
>>          };
>>      }
>>
>> diff -r 8f30f51887d9 test/jdk/com/sun/tools/jextract/constants.h
>> --- a/test/jdk/com/sun/tools/jextract/constants.h       Thu Feb 28 
>> 12:34:49 2019 +0100
>> +++ b/test/jdk/com/sun/tools/jextract/constants.h       Thu Feb 28 
>> 13:29:40 2019 +0100
>> @@ -65,3 +65,4 @@
>>  #define SUB SUP + 2 //dependency
>>
>>  #define ZERO_PTR (void*)0;
>> +#define F_PTR (void*) 0xFFFFFFFFFFFFFFFFLL; // all 1s
>> ```
>>
>> * (I know this was already there); Should the MacroParser.toNumber 
>> fast path use Long.decode instead, to catch more values?
>
> I discussed this with Sundar - we could, but in practice ints cover 
> like 90% of cases; so there was a desire to keep the surface area of 
> the hack small.
>
> Of course if you have real use cases which, like OpenGL, gives a 5x 
> boost when using such an hack, we can revisit!
>
> Maurizio
>
>>
>> ---
>>
>>>> So we have a choice here:
>>>>
>>>> 1) we extract the value of the constant, and we create a plain 
>>>> constant field - e.g.
>>>>
>>>> static final int FOO = 1;
>>>>
>>>> which will then work as before (as a true compile-time constant)
>>>>
>>>> 2) we aim for regularity, and we just translate as
>>>>
>>>> static final int FOO = lib.FOO();
>>
>> My vote is on 1., and when condy eventually becomes available, switch 
>> the more complex constants to that.
>>
>> ---
>>
>> Also, I tested this out with the winreg.h case I had, e.g.:
>>
>> ```
>> typedef struct HKEY__ {
>>     int unused;
>> } *HKEY;
>>
>> typedef unsigned __int64 ULONG_PTR;
>> typedef long LONG;
>>
>> #define HKEY_LOCAL_MACHINE (( HKEY ) (ULONG_PTR)((LONG)0x80000002) )
>> ```
>>
>> But unfortunately no constant was generated for HKEY_LOCAL_MACHINE. 
>> (Note that __int64 is an MSVC extension, maybe that's the problem?)
>>
>> ---
>>
>> On a bit of a tangent; I'm wondering if we really need 2 annotations 
>> for this? Could we instead use one annotation with a `Class carrier` 
>> and `String value` instead? i.e. we encode all constant values as 
>> Strings in the annotation and then reparse them when spinning the 
>> header impl.
>>
>> Jorn
>>
>> Maurizio Cimadamore schreef op 2019-02-28 00:19:
>>> Hi,
>>> here's a new revision where I just slightly improved the TestConstants
>>> test, to be more uniform (instead of passing expected constant values,
>>> the test now passes checker predicates, which is more scalable).
>>>
>>> Webrev:
>>>
>>> http://cr.openjdk.java.net/~mcimadamore/panama/8219822_v3/
>>>
>>> Cheers
>>> Maurizio
>>>
>>>
>>> On 27/02/2019 19:02, Maurizio Cimadamore wrote:
>>>> Hi,
>>>> this patch regularizes support for constant macros (and enum 
>>>> constants too).
>>>>
>>>> http://cr.openjdk.java.net/~mcimadamore/panama/8219822_v2/
>>>>
>>>> The goal of this patch is to stop having jextract generating 
>>>> 'default' methods for constants. Instead, two new annotations are 
>>>> introduced:
>>>>
>>>> @NativeNumericConstant
>>>> @NativeStringConstant
>>>>
>>>> The first takes a long value, the second a String value.
>>>>
>>>> So, given C code like this:
>>>>
>>>> #define FOO 1
>>>>
>>>> instead of generating a method like this:
>>>>
>>>> default int FOO() {
>>>>    return 1;
>>>> }
>>>>
>>>> We will now generate this:
>>>>
>>>> @NativeNumericConstant(1L)
>>>> int FOO();
>>>>
>>>> And then binder will then generate the implementation.
>>>>
>>>> Decoupling the generation of the constant methods from jextract has 
>>>> a big advantage: we can now support complex constant types, such as 
>>>> strings (which need to be turned to Pointer<Byte>) and pointer 
>>>> constants (e.g. (void*)0). Note that, whenever we need some 
>>>> 'constant' pointer, we need to allocate, which means we need a 
>>>> scope - which we don't have at extraction time.
>>>>
>>>> Efficiency-wise, the binder-generated implementation should be as 
>>>> good as the jextract one - it just ldc a constant (which can even 
>>>> be a pointer constant, via CP patching!) and then returns it.
>>>>
>>>> In order to support pointer constants of the kind:
>>>>
>>>> #define PTR (void*)0
>>>>
>>>> I also tweaked MacroParser, so that now two attempts can be made at 
>>>> evaluating the macro:
>>>>
>>>> 1) a first attempt is made using a snippet like this:
>>>>
>>>> __auto_type jextract$var = PTR;
>>>>
>>>> If this fails (and it does fail in this case, as clang cursor 
>>>> evaluation API doesn't detect this constant), then:
>>>>
>>>> 2) we look at the type of the cursor, if the type is a pointer 
>>>> type, then we trigger another snippet parse, this time of:
>>>>
>>>> __auto_type jextract$var = (long)PTR;
>>>>
>>>> The extra cast will effectively reinterpret the value as a numeric 
>>>> constant. Then we'll create a macro whose type is the pointer type 
>>>> determined at (1) and whose value is the one determined at (2).
>>>>
>>>>
>>>> Note that, since we only execute step (2) when the type of the 
>>>> cursor in (1) is a pointer type, we don't end up executing the 
>>>> second step very often. I also tried some of the examples, and the 
>>>> extraction time is the same as before this patch.
>>>>
>>>>
>>>> There is a slight issue with AsmCodeFactoryExt: ideally, we'd like 
>>>> for constant methods to be turned into static constants here; and 
>>>> we'd like to initialize such constants to the result of the 
>>>> computation of the bound constant method - that is, if the library 
>>>> has a method:
>>>>
>>>> @NativeNumericConstant(1L)
>>>> int FOO();
>>>>
>>>> Then, the static wrapper should have the following static field:
>>>>
>>>> static final int FOO = lib.FOO();
>>>>
>>>> However, if we do so, a test will fail, namely LibEnumTest, as that 
>>>> test uses the constants of the static wrapper as labels in a 
>>>> 'switch' statement; this only works if the constant field has the 
>>>> 'ConstantValue' attribute, and that in turn is only possible if the 
>>>> constant is 'simple' - using a condy-based ConstantValue would be a 
>>>> way out, but that is not something that is supported currently, 
>>>> neither by the VM nor by javac.
>>>>
>>>> So we have a choice here:
>>>>
>>>> 1) we extract the value of the constant, and we create a plain 
>>>> constant field - e.g.
>>>>
>>>> static final int FOO = 1;
>>>>
>>>> which will then work as before (as a true compile-time constant)
>>>>
>>>> 2) we aim for regularity, and we just translate as
>>>>
>>>> static final int FOO = lib.FOO();
>>>>
>>>>
>>>> The patch I've submitted does (1) for simple numeric constants and 
>>>> falls back to (2) for complex constants. I'm open to suggestions as 
>>>> to whether it's better to keep this behavior, or simplify it by 
>>>> always aiming for (2).
>>>>
>>>> Maurizio
>>>>
>>>>
>>>>
>>>>