Yes, I am aware of both types of vector shift. Our target VLIW actually supports both and I have implemented all related patterns in our porting. But it would be still nice to allow programmer explicitly use vector shift, preferably both types.
Bingfeng > -----Original Message----- > From: Michael Meissner [mailto:meiss...@linux.vnet.ibm.com] > Sent: 24 February 2009 21:07 > To: Bingfeng Mei > Cc: gcc@gcc.gnu.org > Subject: Re: Native support for vector shift > > On Tue, Feb 24, 2009 at 06:15:37AM -0800, Bingfeng Mei wrote: > > Hello, > > For the targets that support vectors, we can write the > following code: > > > > typedef short V4H __attribute__ ((vector_size (8))); > > > > V4H tst(V4H a, V4H b){ > > return a + b; > > } > > > > Other operators such as -, *, |, &, ^ etc are also > supported. However, vector shift > > is not supported by frontend, including both scalar and > vector second operands. > > > > V4H tst(V4H a, V4H b){ > > return a << 3; > > } > > > > V4H tst(V4H a, V4H b){ > > return a << b; > > } > > > > Currently, we have to use intrinsics to support such shift. > Isn't syntax of vector > > shift intuitive enough to be supported natively? Someone > may argue it breaks the > > C language. But vector is a GCC extension anyway. Support > for vector add/sub/etc > > already break C syntax. Any thought? Sorry if this issue > had been raised in past. > > Note, internally there are two different types of vector > shift. Some machines > support a vector shift by a scalar, some machines support a > vector shift by a > vector. One future machine (x86_64 with -msse5) can support > both types of > vector shifts. > > The auto vectorizer now can deal with both types: > > for (i = 0; i < n; i++) > a[i] = b[i] << c > > will generate a vector shift by a scalar on machines with > that support, and > splat the scalar into a vector for the second set of machines. > > If the machine only has vector shift by a scalar, the auto > vectorizer will not > generate a vector shift for: > > for (i = 0; i < n; i++) > a[i] = b[i] << c[i] > > Internally, the compiler uses the standard shift names for > vector shift by a > scalar (i.e. ashl<type>, ashr<type>, lshl<type>), and a v > prefix for the vector > by vector shifts (i.e. vashl<type>, vashr<type>, vlshl<type>). > > The rotate patterns are also similar. > > -- > Michael Meissner, IBM > 4 Technology Place Drive, MS 2203A, Westford, MA, 01886, USA > meiss...@linux.vnet.ibm.com > >
