From: Matthias Springer <springerm@google.com>
Date: Thu, 21 Oct 2021 12:45:34 +0000 (+0900)
Subject: [mlir][linalg][bufferize] Avoid creating copies that are never read
X-Git-Tag: upstream/15.0.7~28043
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=7a7e93f1225c21b842171d3463bf2158c681dabf;p=platform%2Fupstream%2Fllvm.git

[mlir][linalg][bufferize] Avoid creating copies that are never read

Differential Revision: https://reviews.llvm.org/D111956
---

diff --git a/mlir/lib/Dialect/Linalg/Transforms/ComprehensiveBufferize.cpp b/mlir/lib/Dialect/Linalg/Transforms/ComprehensiveBufferize.cpp
index eb54cee..d31ec52 100644
--- a/mlir/lib/Dialect/Linalg/Transforms/ComprehensiveBufferize.cpp
+++ b/mlir/lib/Dialect/Linalg/Transforms/ComprehensiveBufferize.cpp
@@ -615,11 +615,12 @@ static OpResult getAliasingOpResult(OpOperand &opOperand) {
 // Predeclaration of function.
 static bool bufferizesToMemoryRead(OpOperand &opOperand);
 
-/// scf::ForOp alone doesn't bufferize to a memory read, one of the uses of its
-/// matching bbArg may.
-static bool bufferizesToMemoryRead(scf::ForOp forOp, OpOperand &opOperand) {
+/// Return true if the given value is read by an op that bufferizes to a memory
+/// read. Also takes into account ops that create an alias but do not read by
+/// themselves (e.g., ExtractSliceOp).
+static bool isValueRead(Value value) {
   SmallVector<OpOperand *> workingSet;
-  for (OpOperand &use : forOp.getRegionIterArgForOpOperand(opOperand).getUses())
+  for (OpOperand &use : value.getUses())
     workingSet.push_back(&use);
 
   while (!workingSet.empty()) {
@@ -647,8 +648,10 @@ static bool bufferizesToMemoryRead(OpOperand &opOperand) {
   // may.
   if (isa<ExtractSliceOp>(opOperand.getOwner()))
     return false;
+  // scf::ForOp alone doesn't bufferize to a memory read, one of the uses of its
+  // matching bbArg may.
   if (auto forOp = dyn_cast<scf::ForOp>(opOperand.getOwner()))
-    return bufferizesToMemoryRead(forOp, opOperand);
+    return isValueRead(forOp.getRegionIterArgForOpOperand(opOperand));
   // TiledLoop alone doesn't bufferize to a memory read, one of the uses of its
   // matching bbArg may.
   if (auto tiledLoopOp = dyn_cast<TiledLoopOp>(opOperand.getOwner())) {
@@ -1437,7 +1440,13 @@ static Value getResultBuffer(OpBuilder &b, OpResult result,
     // Allocate the result buffer.
     Value resultBuffer =
         createNewAllocDeallocPairForShapedValue(b, loc, operand, aliasInfo);
-    if (!skipCopy && !isInitTensorOp(operand)) {
+    // Do not copy the result of an InitTensorOp.
+    if (isInitTensorOp(operand))
+      skipCopy = true;
+    // Do not copy if the copied data is never read.
+    if (!isValueRead(result))
+      skipCopy = true;
+    if (!skipCopy) {
       // Set insertion point now that potential alloc/dealloc are introduced.
       b.setInsertionPoint(op);
       b.create<CopyOp>(loc, operandBuffer, resultBuffer);
@@ -2002,7 +2011,9 @@ static LogicalResult bufferize(OpBuilder &b, ExtractSliceOp extractSliceOp,
 
   /// If not inplaceable, copy.
   if (alloc) {
-    b.create<CopyOp>(extractSliceOp.getLoc(), subView, alloc);
+    // Do not copy if the copied data is never read.
+    if (isValueRead(extractSliceOp.result()))
+      b.create<CopyOp>(extractSliceOp.getLoc(), subView, alloc);
     subView = alloc;
   }
 
diff --git a/mlir/test/Dialect/Linalg/comprehensive-module-bufferize.mlir b/mlir/test/Dialect/Linalg/comprehensive-module-bufferize.mlir
index 693974c..b012409 100644
--- a/mlir/test/Dialect/Linalg/comprehensive-module-bufferize.mlir
+++ b/mlir/test/Dialect/Linalg/comprehensive-module-bufferize.mlir
@@ -720,9 +720,6 @@ func @matmul(
         tensor<256x192xf32> to tensor<256x16xf32>
 
       // %4 does not match an insert_slice, it cannot be bufferized inplace and needs to alloc.
-      // CHECK: %[[T:.*]] = memref.subview %[[C]][%[[I]], %[[J]]] [8, 16] [1, 1]
-      // TODO: %4 is never read but just overwritten, this copy can be elided.
-      // CHECK: linalg.copy(%[[T]], %[[ALLOC]])
       %4 = tensor.extract_slice %C[%arg3, %arg5] [8, 16] [1, 1] :
         tensor<128x192xf32> to tensor<8x16xf32>
 
@@ -748,6 +745,7 @@ func @matmul(
       // insert_slice is inplace but its source comes from an equivalent buffer
       // that is not in place. So we must insert a copy of the small buffer into
       // the bigger buffer.
+      // CHECK: %[[T:.*]] = memref.subview %[[C]][%[[I]], %[[J]]] [8, 16] [1, 1]
       // CHECK: linalg.copy(%[[ALLOC]], %[[T]])
       %7 = tensor.insert_slice %6 into %arg6[%arg3, %arg5] [8, 16] [1, 1] :
         tensor<8x16xf32> into tensor<128x192xf32>
@@ -819,9 +817,6 @@ func @buffer_forwarding_conflict(
   // insert_slice. InitTensorOp replaces the init_tensor with an out-of-place
   // extract_slice.
   // CHECK: %[[EXTRACT_SLICE_ALLOC:.*]] = memref.alloc(%[[sz]])
-  // CHECK: %[[T_SUBVIEW:.*]] =  memref.subview %[[FUNC_ARG]][42] [%[[sz]]] [1]
-  // TODO: This copy can be avoided because the copied data is never read.
-  // CHECK: linalg.copy(%[[T_SUBVIEW]], %[[EXTRACT_SLICE_ALLOC]])
   %a = linalg.init_tensor[%sz] : tensor<?xf32>
 
   //     CHECK: linalg.fill({{.*}}, %[[EXTRACT_SLICE_ALLOC]]) : f32, memref<?xf32>
@@ -832,6 +827,7 @@ func @buffer_forwarding_conflict(
   //     CHECK: linalg.copy(%[[EXTRACT_SLICE_ALLOC]], %[[SV0_ALLOC]]) : memref<?xf32>, memref<?xf32>
   %r0 = tensor.insert_slice %f into %t[0][%sz][1]: tensor<?xf32> into tensor<?xf32>
 
+  //     CHECK: %[[T_SUBVIEW:.*]] =  memref.subview %[[FUNC_ARG]][42] [%[[sz]]] [1]
   //     CHECK: linalg.copy(%[[EXTRACT_SLICE_ALLOC]], %[[T_SUBVIEW]])
   %r1 = tensor.insert_slice %f into %t[42][%sz][1]: tensor<?xf32> into tensor<?xf32>