[PATCH] Gather and Scatter intrinsics.

[Elena Demikhovsky]

Hi hfinkel, anemet, nadav, reames,

Gather and Scatter are new introduced intrinsics, comming after recently implemented masked load and store.
This is the first patch for Gather and Scatter intrinsics. A'm asking to review the syntax (we discussed in mails), parsing and verification.

Gather and Scatter intrinsics allow to perform multiple memory accesses (read/write) in one vector instruction.
The intrinsics are not target specific and will have the following syntax:
Gather:
declare <16 x i32> @llvm.masked.gather.v16i32(<16 x i32*> <vector of ptrs>, i32 <alignment>, <16 x i1> <mask>, <16 x i32> <passthru>)
declare <8 x float> @llvm.masked.gather.v8f32(<8 x float*><vector of ptrs>, i32 <alignment>, <8 x i1>  <mask>, <8 x float><passthru>)

Scatter:
declare void @llvm.masked.scatter.v8i32(<8 x i32><vector value to be stored> , <8 x i32*><vector of ptrs> , i32 <alignment>, <8 x i1> <mask>)
declare void @llvm.masked.scatter.v16i32(<16 x i32> <vector value to be stored> , <16 x i32*> <vector of ptrs>, i32 <alignment>, <16 x i1><mask> )

Vector of ptrs - a set of source/destination addresses, to load/store the value. 
Mask - switches on/off vector lanes to prevent memory access for switched-off lanes
vector of ptrs, value and mask should have the same vector width.

These are code examples where gather / scatter should be used and will allow function vectorization
;void foo1(int * __restrict__ A, int * __restrict__ B, int * __restrict__ C) {
;  for (int i=0; i<SIZE; i++) {
;    A[i] = B[C[i]];
;  }
;}

;void foo3(int * __restrict__ A, int * __restrict__ B) {
;  for (int i=0; i<SIZE; i++) {
;    A[B[i]] = i+5;
;  }
;}

REPOSITORY
  rL LLVM

http://reviews.llvm.org/D7433

Files:
  include/llvm/IR/Intrinsics.h
  include/llvm/IR/Intrinsics.td
  lib/IR/Function.cpp
  lib/IR/Verifier.cpp
  utils/TableGen/IntrinsicEmitter.cpp

EMAIL PREFERENCES
  http://reviews.llvm.org/settings/panel/emailpreferences/
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