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[mlir][scf] Always remove for iter args that are loop invariant #121555

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merged 2 commits into from
Jan 3, 2025
Merged

[mlir][scf] Always remove for iter args that are loop invariant #121555

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4ded631
[mlir][scf] Always remove for iter args that are loop invariant
jeffniu-openai Jan 3, 2025
d268464
update doc
jeffniu-openai Jan 3, 2025
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31 changes: 14 additions & 17 deletions mlir/lib/Dialect/SCF/IR/SCF.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -839,8 +839,7 @@ mlir::scf::replaceAndCastForOpIterArg(RewriterBase &rewriter, scf::ForOp forOp,
namespace {
// Fold away ForOp iter arguments when:
// 1) The op yields the iter arguments.
// 2) The iter arguments have no use and the corresponding outer region
// iterators (inputs) are yielded.
// 2) The argument's corresponding outer region iterators (inputs) are yielded.
// 3) The iter arguments have no use and the corresponding (operation) results
// have no use.
//
Expand Down Expand Up @@ -872,30 +871,28 @@ struct ForOpIterArgsFolder : public OpRewritePattern<scf::ForOp> {
newIterArgs.reserve(forOp.getInitArgs().size());
newYieldValues.reserve(numResults);
newResultValues.reserve(numResults);
for (auto it : llvm::zip(forOp.getInitArgs(), // iter from outside
forOp.getRegionIterArgs(), // iter inside region
forOp.getResults(), // op results
forOp.getYieldedValues() // iter yield
)) {
for (auto [init, arg, result, yielded] :
llvm::zip(forOp.getInitArgs(), // iter from outside
forOp.getRegionIterArgs(), // iter inside region
forOp.getResults(), // op results
forOp.getYieldedValues() // iter yield
)) {
// Forwarded is `true` when:
// 1) The region `iter` argument is yielded.
// 2) The region `iter` argument has no use, and the corresponding iter
// operand (input) is yielded.
// 2) The region `iter` argument the corresponding input is yielded.
// 3) The region `iter` argument has no use, and the corresponding op
// result has no use.
bool forwarded = ((std::get<1>(it) == std::get<3>(it)) ||
(std::get<1>(it).use_empty() &&
(std::get<0>(it) == std::get<3>(it) ||
std::get<2>(it).use_empty())));
bool forwarded = (arg == yielded) || (init == yielded) ||
(arg.use_empty() && result.use_empty());
keepMask.push_back(!forwarded);
canonicalize |= forwarded;
if (forwarded) {
newBlockTransferArgs.push_back(std::get<0>(it));
newResultValues.push_back(std::get<0>(it));
newBlockTransferArgs.push_back(init);
newResultValues.push_back(init);
continue;
}
newIterArgs.push_back(std::get<0>(it));
newYieldValues.push_back(std::get<3>(it));
newIterArgs.push_back(init);
newYieldValues.push_back(yielded);
newBlockTransferArgs.push_back(Value()); // placeholder with null value
newResultValues.push_back(Value()); // placeholder with null value
}
Expand Down
22 changes: 18 additions & 4 deletions mlir/test/Dialect/SCF/canonicalize.mlir
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Expand Up @@ -408,6 +408,20 @@ func.func @for_yields_4() -> i32 {

// -----

// CHECK-LABEL: @constant_iter_arg
func.func @constant_iter_arg(%arg0: index, %arg1: index, %arg2: index) {
%c0_i32 = arith.constant 0 : i32
// CHECK: scf.for %arg3 = %arg0 to %arg1 step %arg2 {
%0 = scf.for %i = %arg0 to %arg1 step %arg2 iter_args(%arg3 = %c0_i32) -> i32 {
// CHECK-NEXT: "test.use"(%c0_i32)
"test.use"(%arg3) : (i32) -> ()
scf.yield %c0_i32 : i32
}
return
}

// -----

// CHECK-LABEL: @replace_true_if
func.func @replace_true_if() {
%true = arith.constant true
Expand Down Expand Up @@ -1789,7 +1803,7 @@ module {
}
// CHECK-LABEL: @fold_iter_args_not_being_modified_within_scfforall
// CHECK-SAME: (%{{.*}}: index, %[[ARG1:.*]]: tensor<?xf32>, %[[ARG2:.*]]: tensor<?xf32>) -> (tensor<?xf32>, tensor<?xf32>) {
// CHECK: %[[RESULT:.*]] = scf.forall
// CHECK: %[[RESULT:.*]] = scf.forall
// CHECK-SAME: shared_outs(%[[ITER_ARG_5:.*]] = %[[ARG2]]) -> (tensor<?xf32>) {
// CHECK: %[[OPERAND0:.*]] = tensor.extract_slice %[[ARG1]]
// CHECK: %[[OPERAND1:.*]] = tensor.extract_slice %[[ITER_ARG_5]]
Expand Down Expand Up @@ -1832,7 +1846,7 @@ module {
}
// CHECK-LABEL: @fold_iter_args_with_no_use_of_result_scfforall
// CHECK-SAME: (%{{.*}}: index, %[[ARG1:.*]]: tensor<?xf32>, %[[ARG2:.*]]: tensor<?xf32>, %[[ARG3:.*]]: tensor<?xf32>) -> tensor<?xf32> {
// CHECK: %[[RESULT:.*]] = scf.forall
// CHECK: %[[RESULT:.*]] = scf.forall
// CHECK-SAME: shared_outs(%[[ITER_ARG_6:.*]] = %[[ARG2]]) -> (tensor<?xf32>) {
// CHECK: %[[OPERAND0:.*]] = tensor.extract_slice %[[ARG1]]
// CHECK: %[[OPERAND1:.*]] = tensor.extract_slice %[[ARG3]]
Expand All @@ -1856,7 +1870,7 @@ func.func @index_switch_fold() -> (f32, f32) {
%y = arith.constant 42.0 : f32
scf.yield %y : f32
}

%switch_cst_2 = arith.constant 2: index
%1 = scf.index_switch %switch_cst_2 -> f32
case 0 {
Expand All @@ -1867,7 +1881,7 @@ func.func @index_switch_fold() -> (f32, f32) {
%y = arith.constant 42.0 : f32
scf.yield %y : f32
}

return %0, %1 : f32, f32
}

Expand Down
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