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"Rotem, Nadav" <nadav.rotem at intel.com> writes: > I can think of two ways to represent masks in x86: sparse and > packed. In the sparse method, the masks are kept in <4 x 32bit> > registers, which are mapped to xmm registers. This is the ‘native’ way > of using masks. This argues for the sparse representation, I think. > _Sparse_ After my discussion with

...ers, Nadav -----Original Message----- From: Rotem, Nadav Sent: Thursday, March 10, 2011 11:04 To: 'David A. Greene' Cc: llvmdev at cs.uiuc.edu Subject: RE: [LLVMdev] Vector select/compare support in LLVM Hi David, The MOVMSKPS instruction is cheap (2 cycles). Not to be confused with VMASKMOV, the AVX masked move, which is expensive. One of the arguments for packing masks is that it reduces vector-registers pressure. Auto-vectorizing compilers maintain multiple masks for different execution paths (for each loop nesting, etc). Saving masks in xmm registers may result in vector-regist...

Hello, I started working on adding vector support for the SELECT and CMP instructions in the codegen (bugs: 3384, 1784, 2314).  Currently, the codegen scalarizes vector CMPs into multiple scalar CMPs.  It is easy to add similar scalarization support to the SELECT instruction.  However, using multiple scalar operations is slower than using vector operations. In LLVM, vector-compare operations

...> From: Rotem, Nadav > Sent: Thursday, March 10, 2011 11:04 > To: 'David A. Greene' > Cc: llvmdev at cs.uiuc.edu > Subject: RE: [LLVMdev] Vector select/compare support in LLVM > > Hi David, > > The MOVMSKPS instruction is cheap (2 cycles). Not to be confused with VMASKMOV, the AVX masked move, which is expensive. > > One of the arguments for packing masks is that it reduces vector-registers pressure. Auto-vectorizing compilers maintain multiple masks for different execution paths (for each loop nesting, etc). Saving masks in xmm registers may result in vecto...

Hi David, The MOVMSKPS instruction is cheap (2 cycles). Not to be confused with VMASKMOV, the AVX masked move, which is expensive. One of the arguments for packing masks is that it reduces vector-registers pressure. Auto-vectorizing compilers maintain multiple masks for different execution paths (for each loop nesting, etc). Saving masks in xmm registers may result in vector-regist...