为什么不能gcc或clang正确@encode SIMD矢量类型？ [英] Why can't gcc or clang properly @encode SIMD vector types?

问题描述

在使用向量类型和ObjC运行时做一些错误时，我遇到了一个非常令人困惑的问题。

  #import< Foundation / Foundation.h>对于任何SIMD向量类型， 
 
 int main（）{
 typedef int int4 __attribute __（（vector_size（16）））; 
 typedef float float4 __attribute __（（vector_size（16）））; 
 
 NSLog（@Int4：％s，@encode（int4））; 
 NSLog（@Float4：％s，@encode（float4））; 
} 
  

使用GCC或clang运行，我得到以下输出：

 
 2014-04-09 06：21：01.102 test [1707：507 ] Int4：
 2014-04-09 06：21：01.103 test [1707：507] Float4：
 

我期望，这将是这样的：

 
 2014-04-09 06：21：01.102 test [1707：507] Int4： ！[16,16i] 
 2014-04-09 06:21:01.103 test [1707：507] Float4：！[16,16f] 
 

根据文档此处：

向量     '！['后跟vector_size（组成向量的字节数），后跟逗号，后跟一个向量的对齐方式（以字节为单位），后面紧跟着']'后的元素类型

当试图从ObjC方法返回这些类型时，这变成了一个问题，而不是像！ ，16i] @：用于以下方法的编码：

   - （int4）foo; 
  

我只得到字符串 @：这导致 NSMethodSignature 和 NSInvocation 基本上废除他们的裤子和segfault。

有没有一些编译器选项，我可以启用恢复向量类型的正确编码？或者是这里唯一的解决方案是'不从ObjC方法返回向量'？

注意：返回该向量也没有帮助，因为指针到向量的编码只是 ^ ，然后贪婪匹配列表中的下一个参数，导致我的参数计数再次关闭。我想我可以把向量转换为 void * ，但那真的是一个丑陋的黑客。

解决方案

看起来这是一个已知问题，clang显然已经修改为在这种情况下显示警告： https://github.com/llvm-mirror/clang/commit/024d9c65e9d3887045c82be09e4f630f19da48b4

While doing some messing around with vector types and the ObjC runtime, I came across a very perplexing problem.

Neither clang or GCC will give the 'proper' type-encoding for any SIMD vector type, as far as I can tell.

#import <Foundation/Foundation.h>

int main() {
    typedef int int4 __attribute__((vector_size(16)));
    typedef float float4 __attribute__((vector_size(16)));

    NSLog(@"Int4: %s", @encode(int4));
    NSLog(@"Float4: %s", @encode(float4));
}

When compiled & run with either GCC or clang, I get the following output:

2014-04-09 06:21:01.102 test[1707:507] Int4:
2014-04-09 06:21:01.103 test[1707:507] Float4:

Instead of what I expect, which would be something like this:

2014-04-09 06:21:01.102 test[1707:507] Int4: ![16,16i]
2014-04-09 06:21:01.103 test[1707:507] Float4: ![16,16f]

As per the documentation here:

vectors      ‘![’ followed by the vector_size (the number of bytes composing the vector) followed by a comma, followed by the alignment (in bytes) of the vector, followed by the type of the elements followed by ‘]’

Which becomes a problem when attempting to return these types from an ObjC method, as instead of getting something logical like ![16,16i]@: for the encoding of the following method:

-(int4) foo;

I only get the string @:, which causes both NSMethodSignature and NSInvocation to essentially crap their pants, and segfault.

Is there some compiler option I can enable to restore the proper encoding of vector types? Or is the only solution here 'don't return vectors from an ObjC method'?

Note: Returning (or passing) a pointer to the vector doesn't help either, as the encoding for a pointer-to-vector is simply ^, which then greedily-matches the next argument in the list, causing my argument count to be off once again. I suppose I could cast the vector to a void *, but that really is an ugly hack at that point.

解决方案

Looks like this is a known issue, clang has apparently been modified to show a warning in this case: https://github.com/llvm-mirror/clang/commit/024d9c65e9d3887045c82be09e4f630f19da48b4

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