[BACKEND] add dot conversion (mma version=2) (#672)

LLVM Conversion for Dot op.

Due to the lack of `convert_layout`, currently, the dot only supports
the following combination of operands

- `$a` in shared layout
- `$b` in shared layout
- `$c` in MMA layout(but only Splat-like, leaving the generic cases to
`convert_layout`)

This PR focus on `mma.16816` related logic support, leaving the other
cases to the following PR.

Co-authored-by: Philippe Tillet <phil@openai.com>

lib/Analysis/Allocation.cpp

@@ -43,6 +43,7 @@ getScratchConfigForCvtLayout(triton::gpu::ConvertLayoutOp op, unsigned &inVec,
       return 0;
     }
   };
+  // blocked -> blocked
   if (srcLayout.isa<BlockedEncodingAttr>() &&
       dstLayout.isa<BlockedEncodingAttr>()) {
     auto srcBlockedLayout = srcLayout.cast<BlockedEncodingAttr>();
@@ -65,6 +66,14 @@ getScratchConfigForCvtLayout(triton::gpu::ConvertLayoutOp op, unsigned &inVec,
     }
     paddedRepShape[outOrd[0]] += pad;
   }
+  // blocked -> shared
+  if (srcLayout.isa<BlockedEncodingAttr>() &&
+      dstLayout.isa<SharedEncodingAttr>()) {
+    auto sharedLayout = dstLayout.cast<SharedEncodingAttr>();
+    for (int v : dstTy.getShape())
+      paddedRepShape.push_back(v);
+  }
+
   return paddedRepShape;
 }
 
@@ -131,9 +140,8 @@ private:
       auto dstTy = cvtLayout.result().getType().cast<RankedTensorType>();
       auto srcEncoding = srcTy.getEncoding();
       auto dstEncoding = dstTy.getEncoding();
-      if (srcEncoding.isa<SharedEncodingAttr>() ||
-          dstEncoding.isa<SharedEncodingAttr>()) {
-        // Only blocked -> blocked conversion requires for scratch allocation
+      if (srcEncoding.isa<SharedEncodingAttr>()) {
+        // only block->block and block->shared is supported now
         return;
       }
       // ConvertLayoutOp with both input/output non-shared_layout