Added some ASCII art for encoding documentation

include/triton/Dialect/TritonGPU/IR/TritonGPUAttrDefs.td

@@ -10,15 +10,30 @@ def TritonGPUSharedEncodingAttr : TritonGPU_Attr<"TritonGPUSharedEncoding"> {
   let mnemonic = "shared (memory) encoding";
 
   let description = [{
-    Example:
+An encoding for tensors whose elements may be simultaneously accessed by different warps in the programs, via shared memory.
 
-    ```mlir
-    #SMEM = #triton_gpu.encoding<{
-      vec = 8,
-      perPhase = 8,
-      maxPhase = 1
-    }>
-    ```
+In order to avoid shared memory bank conflicts, elements may be stored in a swizzled layout.
+For example, a swizzled row-major layout stores would store data as follows:
+
+A_{0, 0}  A_{0, 1}  A_{0, 2}  A_{0, 3} ...   [phase 0] \ per_phase = 2
+A_{1, 0}  A_{0, 1}  A_{1, 2}  A_{1, 3} ...   [phase 0] /
+
+groups of vec=2 elements
+are stored contiguously
+_ _ _ _ /\_ _ _ _
+A_{2, 2}  A_{2, 3}  A_{2, 0}  A_{2, 1} ...   [phase 1] \ per phase = 2
+A_{3, 2}  A_{3, 3}  A_{3, 0}  A_{3, 1} ...   [phase 1] /
+
+
+And the associated TritonGPU MLIR
+
+```mlir
+#SMEM = #triton_gpu.encoding<{
+  vec = 2,
+  perPhase = 2,
+  maxPhase = 4
+}>
+```
   }];
 
   let parameters = (
@@ -31,14 +46,41 @@ def TritonGPUSharedEncodingAttr : TritonGPU_Attr<"TritonGPUSharedEncoding"> {
 def TritonGPUCoalescedEncodingAttr : TritonGPU_Attr<"TritonGPUCoalescedEncoding"> {
   let mnemonic = "coalesced encoding";
 
-  let description = [{}];
+  let description = [{
+An encoding where each warp owns a contiguous portion of the target tensor. This is typically the kind of data layout
+consumed (and returned) by LoadInst.
+For example, a row-major coalesced layout may distribute a 32x16 tensor over 2 warps (i.e. 64 threads) as follows:
+
+                          thread tile size 2
+                        - - - - - - /\ - - - - - -
+block|  thread      || A_{0,  0}[T0]   A_{0,  1}[T0]   ... A_{0,  6}[T3]  A_{0,  7}[T3]      A_{0,  8}[T0]  A_{0,  9}[T0]  ... A_{0,  14}[T3]  A_{0,  15}[T3]
+tile |  tile size 2 || A_{1,  0}[T0]   A_{1,  1}[T0]   ... A_{1,  6}[T3]  A_{1,  7}[T3]      A_{1,  8}[T0]  A_{1,  9}[T0]  ... A_{1,  14}[T3]  A_{1,  15}[T3]
+size }  ....
+16   |                 A_{30, 0}[T60]  A_{14, 1}[T60]  ... A_{14, 6}[T63] A_{14, 7}[T63]     A_{14, 8}[T60] A_{14, 9}[T60] ... A_{14, 14}[T63] A_{14, 15}[T63]
+     |                 A_{31, 0}[T60]  A_{15, 1}[T60]  ... A_{15, 6}[T63] A_{15, 7}[T63]     A_{15, 8}[T60] A_{15, 9}[T60] ... A_{15, 14}[T63] A_{15, 15}[T63]
+                      -----------------------------/\-----------------------------------
+                                            block tile size 8
+
+                      A_{16, 0}[T0]   A_{16, 1}[T0]   ... A_{16, 6}[T3]  A_{16, 7}[T3]       A_{16, 8}[T0]  A_{16, 9}[T0]  ... A_{16, 14}[T3]  A_{16, 15}[T3]
+                      A_{17, 0}[T4]   A_{17, 1}[T4]   ... A_{17, 6}[T7]  A_{17, 7}[T7]       A_{17, 8}[T4]  A_{17, 9}[T4]  ... A_{17, 14}[T7]  A_{17, 15}[T7]
+                      ....
+                      A_{30, 0}[T56]  A_{30, 1}[T56]  ... A_{30, 6}[T59] A_{30, 7}[T59]      A_{30, 8}[T56] A_{30, 9}[T56] ... A_{30, 14}[T59] A_{30, 15}[T59]
+                      A_{31, 0}[T60]  A_{31, 1}[T60]  ... A_{31, 6}[T63] A_{31, 7}[T63]      A_{31, 8}[T60] A_{31, 9}[T60] ... A_{31, 14}[T63] A_{31, 15}[T63]
+      
+And the associated TritonGPU MLIR
+#SMEM = #triton_gpu.encoding<{
+  threadTileSize = {2, 2}
+  blockTileSize = {16, 8}
+}>
+ 
+// note to Da: In current Triton codebase, `nanoTileSize = threadTileSize`,  and `macro-tile size = blockTileSize / threadTileSize`
+   probably clearer to have easier semantics (i.e., size of each tile owned by a thread or a block)
+}];
 
   let parameters = (
     ins
-    ArrayRefParameter<"unsigned">:$nanoTileSize,
-    ArrayRefParameter<"unsigned">:$microTileSize,
-    ArrayRefParameter<"unsigned">:$shapePerCTA,
-    ArrayRefParameter<"unsigned">:$reptitions
+    ArrayRefParameter<"unsigned">:$threadTileSize,
+    ArrayRefParameter<"unsigned">:$blockTileSize,
   );
 
   // let genVerifyDecl = 1;
@@ -47,7 +89,7 @@ def TritonGPUCoalescedEncodingAttr : TritonGPU_Attr<"TritonGPUCoalescedEncoding"
 def TritonGPUMmaEncodingAttr : TritonGPU_Attr<"TritonGPUMmaEncoding"> {
   let mnemonic = "mma encoding";
 
-  let description = [{}];
+  let description = [{TODO: I think we may be able to implement it as a special-case of Coalesced encoding with maybe one more warpTileSize attribute!}];
 
   let parameters = (
     ins