diff --git a/mlir/lib/Dialect/Affine/IR/AffineOps.cpp b/mlir/lib/Dialect/Affine/IR/AffineOps.cpp index e0a53cd52f143..be9ca0657a98f 100644 --- a/mlir/lib/Dialect/Affine/IR/AffineOps.cpp +++ b/mlir/lib/Dialect/Affine/IR/AffineOps.cpp @@ -2610,6 +2610,21 @@ static std::optional getTrivialConstantTripCount(AffineForOp forOp) { return ub - lb <= 0 ? 0 : (ub - lb + step - 1) / step; } +/// Calculate the constant value of the loop's induction variable for its last +/// trip. +static std::optional +getConstantInductionVarForLastTrip(AffineForOp forOp) { + std::optional tripCount = getTrivialConstantTripCount(forOp); + if (!tripCount.has_value()) + return std::nullopt; + if (tripCount.value() == 0) + return std::nullopt; + int64_t lb = forOp.getConstantLowerBound(); + int64_t step = forOp.getStepAsInt(); + int64_t lastTripIv = lb + (tripCount.value() - 1) * step; + return lastTripIv; +} + /// Fold the empty loop. static SmallVector AffineForEmptyLoopFolder(AffineForOp forOp) { if (!llvm::hasSingleElement(*forOp.getBody())) @@ -2622,7 +2637,7 @@ static SmallVector AffineForEmptyLoopFolder(AffineForOp forOp) { // results. return forOp.getInits(); } - SmallVector replacements; + SmallVector replacements; auto yieldOp = cast(forOp.getBody()->getTerminator()); auto iterArgs = forOp.getRegionIterArgs(); bool hasValDefinedOutsideLoop = false; @@ -2630,10 +2645,14 @@ static SmallVector AffineForEmptyLoopFolder(AffineForOp forOp) { for (unsigned i = 0, e = yieldOp->getNumOperands(); i < e; ++i) { Value val = yieldOp.getOperand(i); BlockArgument *iterArgIt = llvm::find(iterArgs, val); - // TODO: It should be possible to perform a replacement by computing the - // last value of the IV based on the bounds and the step. - if (val == forOp.getInductionVar()) + if (val == forOp.getInductionVar()) { + if (auto lastTripIv = getConstantInductionVarForLastTrip(forOp)) { + replacements.push_back(IntegerAttr::get( + IndexType::get(forOp.getContext()), lastTripIv.value())); + continue; + } return {}; + } if (iterArgIt == iterArgs.end()) { // `val` is defined outside of the loop. assert(forOp.isDefinedOutsideOfLoop(val) && @@ -2656,7 +2675,7 @@ static SmallVector AffineForEmptyLoopFolder(AffineForOp forOp) { // out of order. if (tripCount.has_value() && tripCount.value() >= 2 && iterArgsNotInOrder) return {}; - return llvm::to_vector_of(replacements); + return llvm::to_vector(replacements); } /// Canonicalize the bounds of the given loop. diff --git a/mlir/test/Dialect/Affine/canonicalize.mlir b/mlir/test/Dialect/Affine/canonicalize.mlir index 1169cd1c29d74..997f23b4bd669 100644 --- a/mlir/test/Dialect/Affine/canonicalize.mlir +++ b/mlir/test/Dialect/Affine/canonicalize.mlir @@ -609,6 +609,19 @@ func.func @fold_zero_iter_loops(%in : index) -> index { // ----- +// CHECK-LABEL: func @fold_empty_loop_iv +// CHECK-SAME: %[[INIT:.*]]: index +func.func @fold_empty_loop_iv(%init: index) -> (index, index) { + %res:2 = affine.for %i = 0 to 10 step 1 iter_args(%arg0 = %init, %arg1 = %init) -> (index, index) { + affine.yield %i, %arg1 : index, index + } + // CHECK: %[[C9:.*]] = arith.constant 9 : index + // CHECK: return %[[C9]], %[[INIT]] : index, index + return %res#0, %res#1 : index, index +} + +// ----- + // CHECK-DAG: #[[$SET:.*]] = affine_set<(d0, d1)[s0] : (d0 >= 0, -d0 + 1022 >= 0, d1 >= 0, -d1 + s0 - 2 >= 0)> // CHECK-LABEL: func @canonicalize_affine_if