[Revert] [Coalesce] Fix the default order to be row major (triton-lang#5707) triton-lang#7143 (triton-lang#7380)

Revert of triton-lang#7143
As per #832 (comment)
Trying to resolve #832 on the
release 3.4.x branch

Author: atalman

include/triton/Dialect/TritonGPU/Transforms/Utility.h

@@ -35,11 +35,9 @@ SmallVector<unsigned, 3> mmaVersionToInstrShape(int version,
 // Return true if the Load uses block pointer.
 bool isLoadFromTensorPtr(triton::LoadOp op);
 
-// Gets the order of a tensor from its contiguity. Places the dimensions with
-// the largest contiguity as the inner most dimension. If the contiguity is
-// all ones, returns the order {dim - 1, dim - 2, ..., 0}
-SmallVector<unsigned, 4>
-getOrderFromContiguity(const SmallVector<int64_t> &contiguity);
+// Return an array of indices enumerating the elements of 'arr' in descending
+// order (so that result[i] is the index of the i-th largest element of 'arr')
+SmallVector<unsigned, 4> argSort(const SmallVector<int64_t> &arr);
 
 // Return the operand used to access the memory in the operation
 Value getMemAccessPtr(Operation *op);

lib/Dialect/TritonGPU/Transforms/Coalesce.cpp

@@ -38,7 +38,7 @@ struct CoalescePass : public impl::TritonGPUCoalesceBase<CoalescePass> {
     });
 
     auto contiguity = axisInfoAnalysis.getAxisInfo(ptr)->getContiguity();
-    SmallVector<unsigned> order = getOrderFromContiguity(contiguity);
+    SmallVector<unsigned> order = argSort(contiguity);
     LDBG("order=[" << triton::join(order, ", ") << "]");
 
     auto matchesShape = [&refTensorType](const Value &val) {
@@ -55,8 +55,8 @@ struct CoalescePass : public impl::TritonGPUCoalesceBase<CoalescePass> {
         Value val = getMemAccessPtr(use);
         if (!val || !matchesShape(val) || memAccessesSameOrder.contains(use))
           continue;
-        auto currOrder = getOrderFromContiguity(
-            axisInfoAnalysis.getAxisInfo(val)->getContiguity());
+        auto currOrder =
+            argSort(axisInfoAnalysis.getAxisInfo(val)->getContiguity());
         if (order == currOrder) {
           LDBG("multi-root-slice: insert to memAccessesSameOrder " << *use);
           memAccessesSameOrder.insert(use);

lib/Dialect/TritonGPU/Transforms/Utility.cpp

@@ -92,11 +92,9 @@ bool isLoadFromTensorPtr(triton::LoadOp op) {
   return mlir::triton::isTensorPointerType(op.getPtr().getType());
 }
 
-SmallVector<unsigned, 4>
-getOrderFromContiguity(const SmallVector<int64_t> &arr) {
+SmallVector<unsigned, 4> argSort(const SmallVector<int64_t> &arr) {
   SmallVector<unsigned, 4> ret(arr.size());
   std::iota(ret.begin(), ret.end(), 0);
-  std::reverse(ret.begin(), ret.end());
   std::stable_sort(ret.begin(), ret.end(),
                    [&](unsigned x, unsigned y) { return arr[x] > arr[y]; });
   return ret;

test/TritonGPU/coalesce.mlir

@@ -199,17 +199,3 @@ tt.func @coalesce_poison(%arg0: !tt.ptr<f16> {tt.divisibility = 16 : i32}, %arg1
 }
 
 }
-
-// -----
-
-#blocked = #ttg.blocked<{sizePerThread = [1, 1, 1], threadsPerWarp = [2, 4, 4], warpsPerCTA = [4, 1, 1], order = [2, 1, 0]}>
-module attributes {"ttg.num-ctas" = 1 : i32, "ttg.num-warps" = 4 : i32, ttg.target = "cuda:100", "ttg.threads-per-warp" = 32 : i32} {
-  tt.func public @load_3D_contig_1(%arg: !tt.ptr<i8> {tt.divisibility = 16 : i32}) attributes {noinline = false} {
-    %50 = tt.splat %arg : !tt.ptr<i8> -> tensor<32x4x4x!tt.ptr<i8>, #blocked>
-    // This checks that the pass picks the row-major ordering by default for elements with contiguity 1.
-    // CHECK: #blocked = #ttg.blocked<{sizePerThread = [1, 1, 1], threadsPerWarp = [2, 4, 4], warpsPerCTA = [4, 1, 1], order = [2, 1, 0]}>
-    // CHECK:  tt.load %1 : tensor<32x4x4x!tt.ptr<i8>, #blocked>
-    %108 = tt.load %50 : tensor<32x4x4x!tt.ptr<i8>, #blocked>
-    tt.return
-  }
-}