Merge triton-mlir branch - Complete rewrite of the backend from scratch (#1004)

This PR merges the `triton-mlir` branch, in which we have been quietly
rewriting the Triton backend from scratch to increase maintainability,
stability and ultimately performance. Changes to the runtime are
minimal, and this new version aims to remain backward-compatible with
the previous commit. The legacy backend is now officially deprecated,
but can still be accessed via the `legacy-backend` tag.

Co-authored-by: Keren Zhou <kerenzhou@openai.com>
Co-authored-by: Yan Chunwei <yanchunwei@outlook.com>
Co-authored-by: goostavz <109190422+goostavz@users.noreply.github.com>
Co-authored-by: Shintaro Iwasaki <siwasaki@fb.com>
Co-authored-by: Yan Da <dyanab@connect.ust.hk>
Co-authored-by: Jun Yang <yangjunpro@gmail.com>
Co-authored-by: Ian Bearman <ianb@microsoft.com>
Co-authored-by: Jason Ansel <jansel@jansel.net>
Co-authored-by: Qingyi Liu <qingyil@nvidia.com>
Co-authored-by: ben-zhang-609 <110140741+ben-zhang-609@users.noreply.github.com>
Co-authored-by: Chenggang Zhao <lyricz@yeah.net>
Co-authored-by: ben-zhang-609 <benzh609@gmail.com>
Co-authored-by: dongdongl <dongdongl@nvidia.com>

lib/Conversion/TritonGPUToLLVM/ElementwiseOpToLLVM.h

@@ -0,0 +1,16 @@
+#ifndef TRITON_CONVERSION_TRITONGPU_TO_ELEMENTWISE_OP_H
+#define TRITON_CONVERSION_TRITONGPU_TO_ELEMENTWISE_OP_H
+
+#include "TritonGPUToLLVMBase.h"
+
+using namespace mlir;
+using namespace mlir::triton;
+
+void populateElementwiseOpToLLVMPatterns(mlir::LLVMTypeConverter &typeConverter,
+                                         RewritePatternSet &patterns,
+                                         int numWarps,
+                                         AxisInfoAnalysis &axisInfoAnalysis,
+                                         const Allocation *allocation,
+                                         Value smem, PatternBenefit benefit);
+
+#endif