[Mlir-commits] [mlir] [Tensor] Simplify tenor.pad tiling length calculations. (PR #119039)

[Nirvedh Meshram]

https://github.com/nirvedhmeshram created https://github.com/llvm/llvm-project/pull/119039

The current calculations calculate ending location of the tiled length and then subtract the new offset from that location. It is possible to directly caculate length. Along with require less operations (which can matter in dynamic case) this also has the advantage that the values are upper bounded by length rather than source size which is more friendly for range analysis. I believe the change is already being tested by 
`test/Dialect/Linalg/subtensor-of-padtensor.mlir` and `test/Dialect/Linalg/tile-and-fuse-tensors.mlir`

>From 6d7024d91a1522d6e53f77a036a1aebda862fbbe Mon Sep 17 00:00:00 2001
From: Nirvedh <nirvedh at gmail.com>
Date: Thu, 5 Dec 2024 18:46:50 -0600
Subject: [PATCH] [Tensor] Simplify tenor.pad tiling length calculations.

Signed-off-by: Nirvedh <nirvedh at gmail.com>
---
 .../Tensor/IR/TensorTilingInterfaceImpl.cpp   | 22 ++++++-------------
 1 file changed, 7 insertions(+), 15 deletions(-)

diff --git a/mlir/lib/Dialect/Tensor/IR/TensorTilingInterfaceImpl.cpp b/mlir/lib/Dialect/Tensor/IR/TensorTilingInterfaceImpl.cpp
index 68c3d1cabb11cb..e647e53bc33af6 100644
--- a/mlir/lib/Dialect/Tensor/IR/TensorTilingInterfaceImpl.cpp
+++ b/mlir/lib/Dialect/Tensor/IR/TensorTilingInterfaceImpl.cpp
@@ -746,11 +746,6 @@ FailureOr<TilingResult> tensor::bubbleUpPadSlice(OpBuilder &b,
   Location loc = padOp->getLoc();
   AffineExpr dim0, dim1;
   bindDims(b.getContext(), dim0, dim1);
-  // Add two integers.
-  auto addMap = AffineMap::get(2, 0, {dim0 + dim1});
-  auto add = [&](OpFoldResult v1, OpFoldResult v2) {
-    return affine::makeComposedFoldedAffineApply(b, loc, addMap, {v1, v2});
-  };
   // Subtract two integers.
   auto subMap = AffineMap::get(2, 0, {dim0 - dim1});
   auto sub = [&](OpFoldResult v1, OpFoldResult v2) {
@@ -825,16 +820,13 @@ FailureOr<TilingResult> tensor::bubbleUpPadSlice(OpBuilder &b,
     // The original read could also have stopped in the high padding zone.
     // In that case, set the end positition of the read should be the end of
     // the source tensor. (Similar to newOffset.)
-    //
-    // endLoc = min(max(offset - low + length, 0), srcSize)
-    //
-    // The new ExtractSliceOp length is `endLoc - newOffset`.
-    //
-    // Optimization: If low = 0, then the formula can be simplified.
-    OpFoldResult endLoc =
-        hasLowPad ? min(max(add(sub(offset, low), length), zero), srcSize)
-                  : min(add(offset, length), srcSize);
-    OpFoldResult newLength = sub(endLoc, newOffset);
+    // srcSize - newOffset represents how much length we have available
+    // and length - newLow represents how much length we want at most.
+    OpFoldResult newLength = min(sub(srcSize, newOffset), sub(length, newLow));
+    // Optimization: If low = 0, then newLow = 0. then newLength >= 0 assuming
+    // length >= 0.
+    if (hasLowPad)
+      newLength = max(newLength, zero);
     newLengths.push_back(newLength);
 
     // Check if newLength is zero. In that case, no SubTensorOp should be