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[LoopUnroll] Do not pipeline epilog loops generated by loop unrolling #5027

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Merged
merged 3 commits into from
Nov 5, 2024
+15 −6
Merged

[LoopUnroll] Do not pipeline epilog loops generated by loop unrolling #5027

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8f28da9
[BACKEND] Do not pipeline epilog loops generated by loop unrolling
htyu Oct 31, 2024
3eb537b
Fix for constant-bound loop where no epilog will be generated.
htyu Oct 31, 2024
6e16e01
Simplified based on MLIR-side changes.
htyu Nov 5, 2024
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20 changes: 14 additions & 6 deletions lib/Dialect/Triton/Transforms/LoopUnroll.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -22,21 +22,22 @@

namespace mlir::triton {

static const char *loopUnrollFactorAttrName = "tt.loop_unroll_factor";

namespace {

class LoopUnrollPass : public TritonLoopUnrollBase<LoopUnrollPass> {

int getUnrollFactorOrDefault(scf::ForOp forOp) {
// Use the attribute attached to the loop if it exists otherwise set the
// factor to 1 to suppress the unrolling.
if (auto factor = forOp->getAttrOfType<IntegerAttr>(
mlir::triton::loopUnrollFactorAttrName))
if (auto factor =
forOp->getAttrOfType<IntegerAttr>(loopUnrollFactorAttrName))
return factor.getInt();
return 1;
}

const char *loopUnrollFactorAttrName = "tt.loop_unroll_factor";
const char *pipelineStagesAttrName = "tt.num_stages";

public:
LoopUnrollPass() = default;
LoopUnrollPass(const LoopUnrollPass &) {}
Expand All @@ -49,11 +50,18 @@ class LoopUnrollPass : public TritonLoopUnrollBase<LoopUnrollPass> {
loops.push_back(forOp);
});

auto ctx = getOperation()->getContext();
for (auto loop : loops) {
auto unrollFactor = getUnrollFactorOrDefault(loop);
loop->removeAttr(mlir::triton::loopUnrollFactorAttrName);
loop->removeAttr(loopUnrollFactorAttrName);
LDBG("Unrolling loop by " << unrollFactor << " times\n" << loop);
(void)loopUnrollByFactor(loop, unrollFactor);
auto resultLoops = loopUnrollByFactor(loop, unrollFactor);
// Do not pipeline the epilog loop.
if (succeeded(resultLoops) && resultLoops->epilogueLoopOp) {
(*resultLoops->epilogueLoopOp)
->setAttr(pipelineStagesAttrName,
mlir::IntegerAttr::get(IntegerType::get(ctx, 32), 1));
}
}
}
};
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1 change: 1 addition & 0 deletions test/Triton/loop-unroll.mlir
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Expand Up @@ -13,6 +13,7 @@ tt.func @add_kernel_unroll(%arg0: tensor<256x!tt.ptr<f32>>, %arg1: i32) {
// CHECK: scf.for
// CHECK: tt.load
// CHECK-NOT: tt.load
// CHECK: tt.num_stages = 1 : i32
%2:2 = scf.for %arg3 = %c1_i32 to %arg1 step %c1_i32 iter_args(%arg4 = %1, %arg5 = %arg0) -> (tensor<256xf32>, tensor<256x!tt.ptr<f32>>) : i32 {
%3 = tt.load %arg5 : tensor<256x!tt.ptr<f32>>
%4 = arith.addf %arg4, %3 : tensor<256xf32>
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