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[mlir][affine-loop-fusion] Fix a bug that AffineIfOp prevents fusion of the other loops 

The presence of AffineIfOp inside AffineFor prevents fusion of the other loops to happen. For example:

```
  affine.for %i0 = 0 to 10 {
    affine.store %cf7, %a[%i0] : memref<10xf32>
  }
  affine.for %i1 = 0 to 10 {
    %v0 = affine.load %a[%i1] : memref<10xf32>
    affine.store %v0, %b[%i1] : memref<10xf32>
  }
  affine.for %i2 = 0 to 10 {
    affine.if #set(%i2) {
      %v0 = affine.load %b[%i2] : memref<10xf32>
    }
  }
```

The first two loops were not be fused because of `affine.if` inside the last `affine.for`.

The issue seems to come from a conservative constraint that does not allow fusion if there are ops whose number of regions != 0 (affine.if is one of them).

This patch just removes such a constraint when`affine.if` is inside `affine.for`.  The existing `canFuseLoops` method is able to handle `affine.if` correctly.

Reviewed By: bondhugula, vinayaka-polymage

Differential Revision: https://reviews.llvm.org/D105963
This commit is contained in:
Tung D. Le 2021-07-30 15:22:21 +05:30 committed by Uday Bondhugula
parent 817f942a28
commit a2186277be
2 changed files with 90 additions and 12 deletions
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15
mlir/lib/Transforms/LoopFusion.cpp
View File

@ -70,19 +70,20 @@ mlir::createLoopFusionPass(unsigned fastMemorySpace,
namespace {
// LoopNestStateCollector walks loop nests and collects load and store
// operations, and whether or not an IfInst was encountered in the loop nest.
// operations, and whether or not a region holding op other than ForOp and IfOp
// was encountered in the loop nest.
struct LoopNestStateCollector {
SmallVector<AffineForOp, 4> forOps;
SmallVector<Operation *, 4> loadOpInsts;
SmallVector<Operation *, 4> storeOpInsts;
bool hasNonForRegion = false;
bool hasNonAffineRegionOp = false;
void collect(Operation *opToWalk) {
opToWalk->walk([&](Operation *op) {
if (isa<AffineForOp>(op))
forOps.push_back(cast<AffineForOp>(op));
else if (op->getNumRegions() != 0)
hasNonForRegion = true;
else if (op->getNumRegions() != 0 && !isa<AffineIfOp>(op))
hasNonAffineRegionOp = true;
else if (isa<AffineReadOpInterface>(op))
loadOpInsts.push_back(op);
else if (isa<AffineWriteOpInterface>(op))
@ -744,9 +745,9 @@ bool MemRefDependenceGraph::init(FuncOp f) {
// all loads and store accesses it contains.
LoopNestStateCollector collector;
collector.collect(&op);
// Return false if a non 'affine.for' region was found (not currently
// supported).
if (collector.hasNonForRegion)
// Return false if a region holding op other than 'affine.for' and
// 'affine.if' was found (not currently supported).
if (collector.hasNonAffineRegionOp)
return false;
Node node(nextNodeId++, &op);
for (auto *opInst : collector.loadOpInsts) {

87
mlir/test/Transforms/loop-fusion.mlir
View File

@ -445,8 +445,8 @@ func @should_fuse_no_top_level_access() {
#set0 = affine_set<(d0) : (1 == 0)>
// CHECK-LABEL: func @should_not_fuse_if_inst_at_top_level() {
func @should_not_fuse_if_inst_at_top_level() {
// CHECK-LABEL: func @should_not_fuse_if_op_at_top_level() {
func @should_not_fuse_if_op_at_top_level() {
%m = memref.alloc() : memref<10xf32>
%cf7 = constant 7.0 : f32
@ -473,8 +473,8 @@ func @should_not_fuse_if_inst_at_top_level() {
#set0 = affine_set<(d0) : (1 == 0)>
// CHECK-LABEL: func @should_not_fuse_if_inst_in_loop_nest() {
func @should_not_fuse_if_inst_in_loop_nest() {
// CHECK-LABEL: func @should_not_fuse_if_op_in_loop_nest() {
func @should_not_fuse_if_op_in_loop_nest() {
%m = memref.alloc() : memref<10xf32>
%cf7 = constant 7.0 : f32
%c4 = constant 4 : index
@ -488,7 +488,7 @@ func @should_not_fuse_if_inst_in_loop_nest() {
%v0 = affine.load %m[%i1] : memref<10xf32>
}
// IfOp in ForInst should prevent fusion.
// IfOp in ForOp should prevent fusion.
// CHECK: affine.for %{{.*}} = 0 to 10 {
// CHECK-NEXT: affine.store %{{.*}}, %{{.*}}[%{{.*}}] : memref<10xf32>
// CHECK-NEXT: }
@ -502,6 +502,83 @@ func @should_not_fuse_if_inst_in_loop_nest() {
// -----
#set = affine_set<(d0) : (d0 - 1 >= 0)>
// CHECK-LABEL: func @should_fuse_if_op_in_loop_nest_not_sandwiched() -> memref<10xf32> {
func @should_fuse_if_op_in_loop_nest_not_sandwiched() -> memref<10xf32> {
%a = memref.alloc() : memref<10xf32>
%b = memref.alloc() : memref<10xf32>
%cf7 = constant 7.0 : f32
affine.for %i0 = 0 to 10 {
affine.store %cf7, %a[%i0] : memref<10xf32>
}
affine.for %i1 = 0 to 10 {
%v0 = affine.load %a[%i1] : memref<10xf32>
affine.store %v0, %b[%i1] : memref<10xf32>
}
affine.for %i2 = 0 to 10 {
affine.if #set(%i2) {
%v0 = affine.load %b[%i2] : memref<10xf32>
}
}
// IfOp in ForOp should not prevent fusion if it does not in between the
// source and dest ForOp ops.
// CHECK: affine.for
// CHECK-NEXT: affine.store
// CHECK-NEXT: affine.load
// CHECK-NEXT: affine.store
// CHECK: affine.for
// CHECK-NEXT: affine.if
// CHECK-NEXT: affine.load
// CHECK-NOT: affine.for
// CHECK: return
return %a : memref<10xf32>
}
// -----
#set = affine_set<(d0) : (d0 - 1 >= 0)>
// CHECK-LABEL: func @should_not_fuse_if_op_in_loop_nest_between_src_and_dest() -> memref<10xf32> {
func @should_not_fuse_if_op_in_loop_nest_between_src_and_dest() -> memref<10xf32> {
%a = memref.alloc() : memref<10xf32>
%b = memref.alloc() : memref<10xf32>
%cf7 = constant 7.0 : f32
affine.for %i0 = 0 to 10 {
affine.store %cf7, %a[%i0] : memref<10xf32>
}
affine.for %i1 = 0 to 10 {
affine.if #set(%i1) {
affine.store %cf7, %a[%i1] : memref<10xf32>
}
}
affine.for %i3 = 0 to 10 {
%v0 = affine.load %a[%i3] : memref<10xf32>
affine.store %v0, %b[%i3] : memref<10xf32>
}
return %b : memref<10xf32>
// IfOp in ForOp which modifies the memref should prevent fusion if it is in
// between the source and dest ForOp.
// CHECK: affine.for
// CHECK-NEXT: affine.store
// CHECK: affine.for
// CHECK-NEXT: affine.if
// CHECK-NEXT: affine.store
// CHECK: affine.for
// CHECK-NEXT: affine.load
// CHECK-NEXT: affine.store
// CHECK: return
}
// -----
// CHECK-LABEL: func @permute_and_fuse() {
func @permute_and_fuse() {
%m = memref.alloc() : memref<10x20x30xf32>