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[flang][StackArrays] track pointers through fir.convert #121919

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Merged
merged 1 commit into from
Jan 8, 2025
Merged

[flang][StackArrays] track pointers through fir.convert #121919

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37 changes: 22 additions & 15 deletions flang/lib/Optimizer/Transforms/StackArrays.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -330,6 +330,18 @@ std::optional<AllocationState> LatticePoint::get(mlir::Value val) const {
return it->second;
}

static mlir::Value lookThroughDeclaresAndConverts(mlir::Value value) {
while (mlir::Operation *op = value.getDefiningOp()) {
if (auto declareOp = llvm::dyn_cast<fir::DeclareOp>(op))
value = declareOp.getMemref();
else if (auto convertOp = llvm::dyn_cast<fir::ConvertOp>(op))
value = convertOp->getOperand(0);
else
return value;
}
return value;
}

mlir::LogicalResult AllocationAnalysis::visitOperation(
mlir::Operation *op, const LatticePoint &before, LatticePoint *after) {
LLVM_DEBUG(llvm::dbgs() << "StackArrays: Visiting operation: " << *op
Expand Down Expand Up @@ -363,10 +375,10 @@ mlir::LogicalResult AllocationAnalysis::visitOperation(
mlir::Value operand = op->getOperand(0);

// Note: StackArrays is scheduled in the pass pipeline after lowering hlfir
// to fir. Therefore, we only need to handle `fir::DeclareOp`s.
if (auto declareOp =
llvm::dyn_cast_if_present<fir::DeclareOp>(operand.getDefiningOp()))
operand = declareOp.getMemref();
// to fir. Therefore, we only need to handle `fir::DeclareOp`s. Also look
// past converts in case the pointer was changed between different pointer
// types.
operand = lookThroughDeclaresAndConverts(operand);

std::optional<AllocationState> operandState = before.get(operand);
if (operandState && *operandState == AllocationState::Allocated) {
Expand Down Expand Up @@ -535,17 +547,12 @@ AllocMemConversion::matchAndRewrite(fir::AllocMemOp allocmem,

// remove freemem operations
llvm::SmallVector<mlir::Operation *> erases;
for (mlir::Operation *user : allocmem.getOperation()->getUsers()) {
if (auto declareOp = mlir::dyn_cast_if_present<fir::DeclareOp>(user)) {
for (mlir::Operation *user : declareOp->getUsers()) {
if (mlir::isa<fir::FreeMemOp>(user))
erases.push_back(user);
}
}

if (mlir::isa<fir::FreeMemOp>(user))
erases.push_back(user);
}
mlir::Operation *parent = allocmem->getParentOp();
// TODO: this shouldn't need to be re-calculated for every allocmem
parent->walk([&](fir::FreeMemOp freeOp) {
if (lookThroughDeclaresAndConverts(freeOp->getOperand(0)) == allocmem)
erases.push_back(freeOp);
});

// now we are done iterating the users, it is safe to mutate them
for (mlir::Operation *erase : erases)
Expand Down
20 changes: 19 additions & 1 deletion flang/test/Transforms/stack-arrays.fir
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Expand Up @@ -379,7 +379,8 @@ func.func @placement_loop_declare() {
%3 = arith.addi %c1, %c2 : index
// operand is now available
%4 = fir.allocmem !fir.array<?xi32>, %3
%5 = fir.declare %4 {uniq_name = "temp"} : (!fir.heap<!fir.array<?xi32>>) -> !fir.heap<!fir.array<?xi32>>
%shape = fir.shape %3 : (index) -> !fir.shape<1>
%5 = fir.declare %4(%shape) {uniq_name = "temp"} : (!fir.heap<!fir.array<?xi32>>, !fir.shape<1>) -> !fir.heap<!fir.array<?xi32>>
// ...
fir.freemem %5 : !fir.heap<!fir.array<?xi32>>
fir.result %3, %c1_i32 : index, i32
Expand All @@ -400,3 +401,20 @@ func.func @placement_loop_declare() {
// CHECK-NEXT: }
// CHECK-NEXT: return
// CHECK-NEXT: }

// Can we look through fir.convert and fir.declare?
func.func @lookthrough() {
%0 = fir.allocmem !fir.array<42xi32>
%c42 = arith.constant 42 : index
%shape = fir.shape %c42 : (index) -> !fir.shape<1>
%1 = fir.declare %0(%shape) {uniq_name = "name"} : (!fir.heap<!fir.array<42xi32>>, !fir.shape<1>) -> !fir.heap<!fir.array<42xi32>>
%2 = fir.convert %1 : (!fir.heap<!fir.array<42xi32>>) -> !fir.ref<!fir.array<42xi32>>
// use the ref so the converts aren't folded
%3 = fir.load %2 : !fir.ref<!fir.array<42xi32>>
%4 = fir.convert %2 : (!fir.ref<!fir.array<42xi32>>) -> !fir.heap<!fir.array<42xi32>>
fir.freemem %4 : !fir.heap<!fir.array<42xi32>>
return
}
// CHECK: func.func @lookthrough() {
// CHECK: fir.alloca !fir.array<42xi32>
// CHECK-NOT: fir.freemem
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