[MLIR][RemoveDeadValues] Privatize public function with NonLive arguments before RDV. #162038
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This diff also changes traversal order from forward to backward for region/block/ops. This order guanratees Liveness updates at a callsite can propagates to the defs of arguments. ``` ./bin/llvm-lit -v ../mlir/test/Transforms/remove-dead-values.mlir ```
Member
|
@llvm/pr-subscribers-mlir Author: xin liu (navyxliu) ChangesThis diff is REDO of #160242. ProblemLiveness analysis is inter-procedural. If there are some unused arguments in a public function, they propagate to callers. From the perspective of RemoveDeadValues, the signature of a public function is immutable. It can't cope with this situation. One side, it deletes outgoing arguments, on the other side it keeps the function intact. SolutionWe deploy two methods to fix this bug.
Test planFull diff: https://github.com/llvm/llvm-project/pull/162038.diff 4 Files Affected:
diff --git a/mlir/include/mlir/Analysis/DataFlow/LivenessAnalysis.h b/mlir/include/mlir/Analysis/DataFlow/LivenessAnalysis.h
index cf1fd6e2d48ca..be7e027b95f64 100644
--- a/mlir/include/mlir/Analysis/DataFlow/LivenessAnalysis.h
+++ b/mlir/include/mlir/Analysis/DataFlow/LivenessAnalysis.h
@@ -102,6 +102,9 @@ struct RunLivenessAnalysis {
const Liveness *getLiveness(Value val);
+ /// Return the configuration of the solver used for this analysis.
+ const DataFlowConfig &getSolverConfig() const { return solver.getConfig(); }
+
private:
/// Stores the result of the liveness analysis that was run.
DataFlowSolver solver;
diff --git a/mlir/include/mlir/IR/Visitors.h b/mlir/include/mlir/IR/Visitors.h
index 893f66ae33deb..5766d262796d6 100644
--- a/mlir/include/mlir/IR/Visitors.h
+++ b/mlir/include/mlir/IR/Visitors.h
@@ -39,6 +39,20 @@ struct ForwardIterator {
}
};
+/// This iterator enumerates the elements in "backward" order.
+struct BackwardIterator {
+ template <typename T>
+ static auto makeIterable(T &range) {
+ if constexpr (std::is_same<T, Operation>()) {
+ /// Make operations iterable: return the list of regions.
+ return llvm::reverse(range.getRegions());
+ } else {
+ /// Regions and block are already iterable.
+ return llvm::reverse(range);
+ }
+ }
+};
+
/// A utility class to encode the current walk stage for "generic" walkers.
/// When walking an operation, we can either choose a Pre/Post order walker
/// which invokes the callback on an operation before/after all its attached
diff --git a/mlir/lib/Transforms/RemoveDeadValues.cpp b/mlir/lib/Transforms/RemoveDeadValues.cpp
index e0c65b0e09774..ed5c6a8d2ead0 100644
--- a/mlir/lib/Transforms/RemoveDeadValues.cpp
+++ b/mlir/lib/Transforms/RemoveDeadValues.cpp
@@ -33,6 +33,7 @@
#include "mlir/Analysis/DataFlow/DeadCodeAnalysis.h"
#include "mlir/Analysis/DataFlow/LivenessAnalysis.h"
+#include "mlir/Dialect/Arith/IR/Arith.h"
#include "mlir/IR/Builders.h"
#include "mlir/IR/BuiltinAttributes.h"
#include "mlir/IR/Dialect.h"
@@ -118,8 +119,13 @@ struct RDVFinalCleanupList {
/// Return true iff at least one value in `values` is live, given the liveness
/// information in `la`.
static bool hasLive(ValueRange values, const DenseSet<Value> &nonLiveSet,
- RunLivenessAnalysis &la) {
+ const DenseSet<Value> &liveSet, RunLivenessAnalysis &la) {
for (Value value : values) {
+ if (liveSet.contains(value)) {
+ LDBG() << "Value " << value << " is marked live by CallOp";
+ return true;
+ }
+
if (nonLiveSet.contains(value)) {
LDBG() << "Value " << value << " is already marked non-live (dead)";
continue;
@@ -144,6 +150,7 @@ static bool hasLive(ValueRange values, const DenseSet<Value> &nonLiveSet,
/// Return a BitVector of size `values.size()` where its i-th bit is 1 iff the
/// i-th value in `values` is live, given the liveness information in `la`.
static BitVector markLives(ValueRange values, const DenseSet<Value> &nonLiveSet,
+ const DenseSet<Value> &liveSet,
RunLivenessAnalysis &la) {
BitVector lives(values.size(), true);
@@ -154,7 +161,9 @@ static BitVector markLives(ValueRange values, const DenseSet<Value> &nonLiveSet,
<< " is already marked non-live (dead) at index " << index;
continue;
}
-
+ if (liveSet.contains(value)) {
+ continue;
+ }
const Liveness *liveness = la.getLiveness(value);
// It is important to note that when `liveness` is null, we can't tell if
// `value` is live or not. So, the safe option is to consider it live. Also,
@@ -259,8 +268,19 @@ static SmallVector<OpOperand *> operandsToOpOperands(OperandRange operands) {
/// - Return-like
static void processSimpleOp(Operation *op, RunLivenessAnalysis &la,
DenseSet<Value> &nonLiveSet,
- RDVFinalCleanupList &cl) {
- if (!isMemoryEffectFree(op) || hasLive(op->getResults(), nonLiveSet, la)) {
+ DenseSet<Value> &liveSet, RDVFinalCleanupList &cl) {
+ for (Value val : op->getResults()) {
+ if (liveSet.contains(val)) {
+ LDBG() << "Simple op is used by a public function, "
+ "preserving it: "
+ << OpWithFlags(op, OpPrintingFlags().skipRegions());
+ liveSet.insert_range(op->getOperands());
+ return;
+ }
+ }
+
+ if (!isMemoryEffectFree(op) ||
+ hasLive(op->getResults(), nonLiveSet, liveSet, la)) {
LDBG() << "Simple op is not memory effect free or has live results, "
"preserving it: "
<< OpWithFlags(op, OpPrintingFlags().skipRegions());
@@ -288,7 +308,7 @@ static void processSimpleOp(Operation *op, RunLivenessAnalysis &la,
/// (6) Marking all its results as non-live values.
static void processFuncOp(FunctionOpInterface funcOp, Operation *module,
RunLivenessAnalysis &la, DenseSet<Value> &nonLiveSet,
- RDVFinalCleanupList &cl) {
+ DenseSet<Value> &liveSet, RDVFinalCleanupList &cl) {
LDBG() << "Processing function op: "
<< OpWithFlags(funcOp, OpPrintingFlags().skipRegions());
if (funcOp.isPublic() || funcOp.isExternal()) {
@@ -299,7 +319,7 @@ static void processFuncOp(FunctionOpInterface funcOp, Operation *module,
// Get the list of unnecessary (non-live) arguments in `nonLiveArgs`.
SmallVector<Value> arguments(funcOp.getArguments());
- BitVector nonLiveArgs = markLives(arguments, nonLiveSet, la);
+ BitVector nonLiveArgs = markLives(arguments, nonLiveSet, liveSet, la);
nonLiveArgs = nonLiveArgs.flip();
// Do (1).
@@ -352,7 +372,8 @@ static void processFuncOp(FunctionOpInterface funcOp, Operation *module,
for (SymbolTable::SymbolUse use : uses) {
Operation *callOp = use.getUser();
assert(isa<CallOpInterface>(callOp) && "expected a call-like user");
- BitVector liveCallRets = markLives(callOp->getResults(), nonLiveSet, la);
+ BitVector liveCallRets =
+ markLives(callOp->getResults(), nonLiveSet, liveSet, la);
nonLiveRets &= liveCallRets.flip();
}
@@ -379,6 +400,56 @@ static void processFuncOp(FunctionOpInterface funcOp, Operation *module,
}
}
+// Create a cheaper value with the same type of oldVal in front of CallOp.
+static Value createDummyArgument(CallOpInterface callOp, Value oldVal) {
+ OpBuilder builder(callOp.getOperation());
+ Type type = oldVal.getType();
+
+ // Create zero constant for any supported type
+ if (TypedAttr zeroAttr = builder.getZeroAttr(type)) {
+ return builder.create<arith::ConstantOp>(oldVal.getLoc(), type, zeroAttr);
+ }
+ return {};
+}
+
+static void processCallOp(CallOpInterface callOp, Operation *module,
+ RunLivenessAnalysis &la, DenseSet<Value> &nonLiveSet,
+ DenseSet<Value> &liveSet) {
+ if (!la.getSolverConfig().isInterprocedural())
+ return;
+
+ Operation *callableOp = callOp.resolveCallable();
+ auto funcOp = dyn_cast<FunctionOpInterface>(callableOp);
+ if (!funcOp || !funcOp.isPublic()) {
+ return;
+ }
+
+ LDBG() << "processCallOp to a public function: " << funcOp.getName();
+ // Get the list of unnecessary (non-live) arguments in `nonLiveArgs`.
+ SmallVector<Value> arguments(funcOp.getArguments());
+ BitVector nonLiveArgs = markLives(arguments, nonLiveSet, liveSet, la);
+ nonLiveArgs = nonLiveArgs.flip();
+
+ if (nonLiveArgs.count() > 0) {
+ LDBG() << funcOp.getName() << " contains NonLive arguments";
+ // The number of operands in the call op may not match the number of
+ // arguments in the func op.
+ SmallVector<OpOperand *> callOpOperands =
+ operandsToOpOperands(callOp.getArgOperands());
+
+ for (int index : nonLiveArgs.set_bits()) {
+ OpOperand *operand = callOpOperands[index];
+ Value oldVal = operand->get();
+ if (Value dummy = createDummyArgument(callOp, oldVal)) {
+ callOp->setOperand(operand->getOperandNumber(), dummy);
+ nonLiveSet.insert(oldVal);
+ } else {
+ liveSet.insert(oldVal);
+ }
+ }
+ }
+}
+
/// Process a region branch operation `regionBranchOp` using the liveness
/// information in `la`. The processing involves two scenarios:
///
@@ -411,12 +482,14 @@ static void processFuncOp(FunctionOpInterface funcOp, Operation *module,
static void processRegionBranchOp(RegionBranchOpInterface regionBranchOp,
RunLivenessAnalysis &la,
DenseSet<Value> &nonLiveSet,
+ DenseSet<Value> &liveSet,
RDVFinalCleanupList &cl) {
LDBG() << "Processing region branch op: "
<< OpWithFlags(regionBranchOp, OpPrintingFlags().skipRegions());
// Mark live results of `regionBranchOp` in `liveResults`.
auto markLiveResults = [&](BitVector &liveResults) {
- liveResults = markLives(regionBranchOp->getResults(), nonLiveSet, la);
+ liveResults =
+ markLives(regionBranchOp->getResults(), nonLiveSet, liveSet, la);
};
// Mark live arguments in the regions of `regionBranchOp` in `liveArgs`.
@@ -425,7 +498,7 @@ static void processRegionBranchOp(RegionBranchOpInterface regionBranchOp,
if (region.empty())
continue;
SmallVector<Value> arguments(region.front().getArguments());
- BitVector regionLiveArgs = markLives(arguments, nonLiveSet, la);
+ BitVector regionLiveArgs = markLives(arguments, nonLiveSet, liveSet, la);
liveArgs[®ion] = regionLiveArgs;
}
};
@@ -619,7 +692,7 @@ static void processRegionBranchOp(RegionBranchOpInterface regionBranchOp,
// attributed to something else.
// Do (1') and (2').
if (isMemoryEffectFree(regionBranchOp.getOperation()) &&
- !hasLive(regionBranchOp->getResults(), nonLiveSet, la)) {
+ !hasLive(regionBranchOp->getResults(), nonLiveSet, liveSet, la)) {
cl.operations.push_back(regionBranchOp.getOperation());
return;
}
@@ -698,7 +771,7 @@ static void processRegionBranchOp(RegionBranchOpInterface regionBranchOp,
static void processBranchOp(BranchOpInterface branchOp, RunLivenessAnalysis &la,
DenseSet<Value> &nonLiveSet,
- RDVFinalCleanupList &cl) {
+ DenseSet<Value> &liveSet, RDVFinalCleanupList &cl) {
LDBG() << "Processing branch op: " << *branchOp;
unsigned numSuccessors = branchOp->getNumSuccessors();
@@ -716,7 +789,7 @@ static void processBranchOp(BranchOpInterface branchOp, RunLivenessAnalysis &la,
// Do (2)
BitVector successorNonLive =
- markLives(operandValues, nonLiveSet, la).flip();
+ markLives(operandValues, nonLiveSet, liveSet, la).flip();
collectNonLiveValues(nonLiveSet, successorBlock->getArguments(),
successorNonLive);
@@ -876,26 +949,29 @@ void RemoveDeadValues::runOnOperation() {
// Tracks values eligible for erasure - complements liveness analysis to
// identify "droppable" values.
DenseSet<Value> deadVals;
+ // mark outgoing arguments to a public function LIVE. We also propagate
+ // liveness backward.
+ DenseSet<Value> liveVals;
// Maintains a list of Ops, values, branches, etc., slated for cleanup at the
// end of this pass.
RDVFinalCleanupList finalCleanupList;
- module->walk([&](Operation *op) {
+ module->walk<WalkOrder::PostOrder, BackwardIterator>([&](Operation *op) {
if (auto funcOp = dyn_cast<FunctionOpInterface>(op)) {
- processFuncOp(funcOp, module, la, deadVals, finalCleanupList);
+ processFuncOp(funcOp, module, la, deadVals, liveVals, finalCleanupList);
} else if (auto regionBranchOp = dyn_cast<RegionBranchOpInterface>(op)) {
- processRegionBranchOp(regionBranchOp, la, deadVals, finalCleanupList);
+ processRegionBranchOp(regionBranchOp, la, deadVals, liveVals,
+ finalCleanupList);
} else if (auto branchOp = dyn_cast<BranchOpInterface>(op)) {
- processBranchOp(branchOp, la, deadVals, finalCleanupList);
+ processBranchOp(branchOp, la, deadVals, liveVals, finalCleanupList);
} else if (op->hasTrait<::mlir::OpTrait::IsTerminator>()) {
// Nothing to do here because this is a terminator op and it should be
// honored with respect to its parent
} else if (isa<CallOpInterface>(op)) {
- // Nothing to do because this op is associated with a function op and gets
- // cleaned when the latter is cleaned.
+ processCallOp(cast<CallOpInterface>(op), module, la, deadVals, liveVals);
} else {
- processSimpleOp(op, la, deadVals, finalCleanupList);
+ processSimpleOp(op, la, deadVals, liveVals, finalCleanupList);
}
});
diff --git a/mlir/test/Transforms/remove-dead-values.mlir b/mlir/test/Transforms/remove-dead-values.mlir
index 56449469dc29f..ebb76a8835ceb 100644
--- a/mlir/test/Transforms/remove-dead-values.mlir
+++ b/mlir/test/Transforms/remove-dead-values.mlir
@@ -569,6 +569,24 @@ module @return_void_with_unused_argument {
call @fn_return_void_with_unused_argument(%arg0, %unused) : (i32, memref<4xi32>) -> ()
return %unused : memref<4xi32>
}
+
+ // the function signature is immutable because it is public.
+ func.func public @immutable_fn_with_unused_argument(%arg0: i32, %arg1: memref<4xf32>) -> () {
+ return
+ }
+
+ // CHECK-LABEL: func.func @main2
+ // CHECK: %[[MEM:.*]] = memref.alloc() : memref<4xf32>
+ // CHECK: %[[UNUSED:.*]] = arith.constant 0 : i32
+ // CHECK: call @immutable_fn_with_unused_argument(%[[UNUSED]], %[[MEM]]) : (i32, memref<4xf32>) -> ()
+ func.func @main2() -> () {
+ %one = arith.constant 1 : i32
+ %scalar = arith.addi %one, %one: i32
+ %mem = memref.alloc() : memref<4xf32>
+
+ call @immutable_fn_with_unused_argument(%scalar, %mem) : (i32, memref<4xf32>) -> ()
+ return
+ }
}
// -----
|
Member
|
@llvm/pr-subscribers-mlir-core Author: xin liu (navyxliu) ChangesThis diff is REDO of #160242. ProblemLiveness analysis is inter-procedural. If there are some unused arguments in a public function, they propagate to callers. From the perspective of RemoveDeadValues, the signature of a public function is immutable. It can't cope with this situation. One side, it deletes outgoing arguments, on the other side it keeps the function intact. SolutionWe deploy two methods to fix this bug.
Test planFull diff: https://github.com/llvm/llvm-project/pull/162038.diff 4 Files Affected:
diff --git a/mlir/include/mlir/Analysis/DataFlow/LivenessAnalysis.h b/mlir/include/mlir/Analysis/DataFlow/LivenessAnalysis.h
index cf1fd6e2d48ca..be7e027b95f64 100644
--- a/mlir/include/mlir/Analysis/DataFlow/LivenessAnalysis.h
+++ b/mlir/include/mlir/Analysis/DataFlow/LivenessAnalysis.h
@@ -102,6 +102,9 @@ struct RunLivenessAnalysis {
const Liveness *getLiveness(Value val);
+ /// Return the configuration of the solver used for this analysis.
+ const DataFlowConfig &getSolverConfig() const { return solver.getConfig(); }
+
private:
/// Stores the result of the liveness analysis that was run.
DataFlowSolver solver;
diff --git a/mlir/include/mlir/IR/Visitors.h b/mlir/include/mlir/IR/Visitors.h
index 893f66ae33deb..5766d262796d6 100644
--- a/mlir/include/mlir/IR/Visitors.h
+++ b/mlir/include/mlir/IR/Visitors.h
@@ -39,6 +39,20 @@ struct ForwardIterator {
}
};
+/// This iterator enumerates the elements in "backward" order.
+struct BackwardIterator {
+ template <typename T>
+ static auto makeIterable(T &range) {
+ if constexpr (std::is_same<T, Operation>()) {
+ /// Make operations iterable: return the list of regions.
+ return llvm::reverse(range.getRegions());
+ } else {
+ /// Regions and block are already iterable.
+ return llvm::reverse(range);
+ }
+ }
+};
+
/// A utility class to encode the current walk stage for "generic" walkers.
/// When walking an operation, we can either choose a Pre/Post order walker
/// which invokes the callback on an operation before/after all its attached
diff --git a/mlir/lib/Transforms/RemoveDeadValues.cpp b/mlir/lib/Transforms/RemoveDeadValues.cpp
index e0c65b0e09774..ed5c6a8d2ead0 100644
--- a/mlir/lib/Transforms/RemoveDeadValues.cpp
+++ b/mlir/lib/Transforms/RemoveDeadValues.cpp
@@ -33,6 +33,7 @@
#include "mlir/Analysis/DataFlow/DeadCodeAnalysis.h"
#include "mlir/Analysis/DataFlow/LivenessAnalysis.h"
+#include "mlir/Dialect/Arith/IR/Arith.h"
#include "mlir/IR/Builders.h"
#include "mlir/IR/BuiltinAttributes.h"
#include "mlir/IR/Dialect.h"
@@ -118,8 +119,13 @@ struct RDVFinalCleanupList {
/// Return true iff at least one value in `values` is live, given the liveness
/// information in `la`.
static bool hasLive(ValueRange values, const DenseSet<Value> &nonLiveSet,
- RunLivenessAnalysis &la) {
+ const DenseSet<Value> &liveSet, RunLivenessAnalysis &la) {
for (Value value : values) {
+ if (liveSet.contains(value)) {
+ LDBG() << "Value " << value << " is marked live by CallOp";
+ return true;
+ }
+
if (nonLiveSet.contains(value)) {
LDBG() << "Value " << value << " is already marked non-live (dead)";
continue;
@@ -144,6 +150,7 @@ static bool hasLive(ValueRange values, const DenseSet<Value> &nonLiveSet,
/// Return a BitVector of size `values.size()` where its i-th bit is 1 iff the
/// i-th value in `values` is live, given the liveness information in `la`.
static BitVector markLives(ValueRange values, const DenseSet<Value> &nonLiveSet,
+ const DenseSet<Value> &liveSet,
RunLivenessAnalysis &la) {
BitVector lives(values.size(), true);
@@ -154,7 +161,9 @@ static BitVector markLives(ValueRange values, const DenseSet<Value> &nonLiveSet,
<< " is already marked non-live (dead) at index " << index;
continue;
}
-
+ if (liveSet.contains(value)) {
+ continue;
+ }
const Liveness *liveness = la.getLiveness(value);
// It is important to note that when `liveness` is null, we can't tell if
// `value` is live or not. So, the safe option is to consider it live. Also,
@@ -259,8 +268,19 @@ static SmallVector<OpOperand *> operandsToOpOperands(OperandRange operands) {
/// - Return-like
static void processSimpleOp(Operation *op, RunLivenessAnalysis &la,
DenseSet<Value> &nonLiveSet,
- RDVFinalCleanupList &cl) {
- if (!isMemoryEffectFree(op) || hasLive(op->getResults(), nonLiveSet, la)) {
+ DenseSet<Value> &liveSet, RDVFinalCleanupList &cl) {
+ for (Value val : op->getResults()) {
+ if (liveSet.contains(val)) {
+ LDBG() << "Simple op is used by a public function, "
+ "preserving it: "
+ << OpWithFlags(op, OpPrintingFlags().skipRegions());
+ liveSet.insert_range(op->getOperands());
+ return;
+ }
+ }
+
+ if (!isMemoryEffectFree(op) ||
+ hasLive(op->getResults(), nonLiveSet, liveSet, la)) {
LDBG() << "Simple op is not memory effect free or has live results, "
"preserving it: "
<< OpWithFlags(op, OpPrintingFlags().skipRegions());
@@ -288,7 +308,7 @@ static void processSimpleOp(Operation *op, RunLivenessAnalysis &la,
/// (6) Marking all its results as non-live values.
static void processFuncOp(FunctionOpInterface funcOp, Operation *module,
RunLivenessAnalysis &la, DenseSet<Value> &nonLiveSet,
- RDVFinalCleanupList &cl) {
+ DenseSet<Value> &liveSet, RDVFinalCleanupList &cl) {
LDBG() << "Processing function op: "
<< OpWithFlags(funcOp, OpPrintingFlags().skipRegions());
if (funcOp.isPublic() || funcOp.isExternal()) {
@@ -299,7 +319,7 @@ static void processFuncOp(FunctionOpInterface funcOp, Operation *module,
// Get the list of unnecessary (non-live) arguments in `nonLiveArgs`.
SmallVector<Value> arguments(funcOp.getArguments());
- BitVector nonLiveArgs = markLives(arguments, nonLiveSet, la);
+ BitVector nonLiveArgs = markLives(arguments, nonLiveSet, liveSet, la);
nonLiveArgs = nonLiveArgs.flip();
// Do (1).
@@ -352,7 +372,8 @@ static void processFuncOp(FunctionOpInterface funcOp, Operation *module,
for (SymbolTable::SymbolUse use : uses) {
Operation *callOp = use.getUser();
assert(isa<CallOpInterface>(callOp) && "expected a call-like user");
- BitVector liveCallRets = markLives(callOp->getResults(), nonLiveSet, la);
+ BitVector liveCallRets =
+ markLives(callOp->getResults(), nonLiveSet, liveSet, la);
nonLiveRets &= liveCallRets.flip();
}
@@ -379,6 +400,56 @@ static void processFuncOp(FunctionOpInterface funcOp, Operation *module,
}
}
+// Create a cheaper value with the same type of oldVal in front of CallOp.
+static Value createDummyArgument(CallOpInterface callOp, Value oldVal) {
+ OpBuilder builder(callOp.getOperation());
+ Type type = oldVal.getType();
+
+ // Create zero constant for any supported type
+ if (TypedAttr zeroAttr = builder.getZeroAttr(type)) {
+ return builder.create<arith::ConstantOp>(oldVal.getLoc(), type, zeroAttr);
+ }
+ return {};
+}
+
+static void processCallOp(CallOpInterface callOp, Operation *module,
+ RunLivenessAnalysis &la, DenseSet<Value> &nonLiveSet,
+ DenseSet<Value> &liveSet) {
+ if (!la.getSolverConfig().isInterprocedural())
+ return;
+
+ Operation *callableOp = callOp.resolveCallable();
+ auto funcOp = dyn_cast<FunctionOpInterface>(callableOp);
+ if (!funcOp || !funcOp.isPublic()) {
+ return;
+ }
+
+ LDBG() << "processCallOp to a public function: " << funcOp.getName();
+ // Get the list of unnecessary (non-live) arguments in `nonLiveArgs`.
+ SmallVector<Value> arguments(funcOp.getArguments());
+ BitVector nonLiveArgs = markLives(arguments, nonLiveSet, liveSet, la);
+ nonLiveArgs = nonLiveArgs.flip();
+
+ if (nonLiveArgs.count() > 0) {
+ LDBG() << funcOp.getName() << " contains NonLive arguments";
+ // The number of operands in the call op may not match the number of
+ // arguments in the func op.
+ SmallVector<OpOperand *> callOpOperands =
+ operandsToOpOperands(callOp.getArgOperands());
+
+ for (int index : nonLiveArgs.set_bits()) {
+ OpOperand *operand = callOpOperands[index];
+ Value oldVal = operand->get();
+ if (Value dummy = createDummyArgument(callOp, oldVal)) {
+ callOp->setOperand(operand->getOperandNumber(), dummy);
+ nonLiveSet.insert(oldVal);
+ } else {
+ liveSet.insert(oldVal);
+ }
+ }
+ }
+}
+
/// Process a region branch operation `regionBranchOp` using the liveness
/// information in `la`. The processing involves two scenarios:
///
@@ -411,12 +482,14 @@ static void processFuncOp(FunctionOpInterface funcOp, Operation *module,
static void processRegionBranchOp(RegionBranchOpInterface regionBranchOp,
RunLivenessAnalysis &la,
DenseSet<Value> &nonLiveSet,
+ DenseSet<Value> &liveSet,
RDVFinalCleanupList &cl) {
LDBG() << "Processing region branch op: "
<< OpWithFlags(regionBranchOp, OpPrintingFlags().skipRegions());
// Mark live results of `regionBranchOp` in `liveResults`.
auto markLiveResults = [&](BitVector &liveResults) {
- liveResults = markLives(regionBranchOp->getResults(), nonLiveSet, la);
+ liveResults =
+ markLives(regionBranchOp->getResults(), nonLiveSet, liveSet, la);
};
// Mark live arguments in the regions of `regionBranchOp` in `liveArgs`.
@@ -425,7 +498,7 @@ static void processRegionBranchOp(RegionBranchOpInterface regionBranchOp,
if (region.empty())
continue;
SmallVector<Value> arguments(region.front().getArguments());
- BitVector regionLiveArgs = markLives(arguments, nonLiveSet, la);
+ BitVector regionLiveArgs = markLives(arguments, nonLiveSet, liveSet, la);
liveArgs[®ion] = regionLiveArgs;
}
};
@@ -619,7 +692,7 @@ static void processRegionBranchOp(RegionBranchOpInterface regionBranchOp,
// attributed to something else.
// Do (1') and (2').
if (isMemoryEffectFree(regionBranchOp.getOperation()) &&
- !hasLive(regionBranchOp->getResults(), nonLiveSet, la)) {
+ !hasLive(regionBranchOp->getResults(), nonLiveSet, liveSet, la)) {
cl.operations.push_back(regionBranchOp.getOperation());
return;
}
@@ -698,7 +771,7 @@ static void processRegionBranchOp(RegionBranchOpInterface regionBranchOp,
static void processBranchOp(BranchOpInterface branchOp, RunLivenessAnalysis &la,
DenseSet<Value> &nonLiveSet,
- RDVFinalCleanupList &cl) {
+ DenseSet<Value> &liveSet, RDVFinalCleanupList &cl) {
LDBG() << "Processing branch op: " << *branchOp;
unsigned numSuccessors = branchOp->getNumSuccessors();
@@ -716,7 +789,7 @@ static void processBranchOp(BranchOpInterface branchOp, RunLivenessAnalysis &la,
// Do (2)
BitVector successorNonLive =
- markLives(operandValues, nonLiveSet, la).flip();
+ markLives(operandValues, nonLiveSet, liveSet, la).flip();
collectNonLiveValues(nonLiveSet, successorBlock->getArguments(),
successorNonLive);
@@ -876,26 +949,29 @@ void RemoveDeadValues::runOnOperation() {
// Tracks values eligible for erasure - complements liveness analysis to
// identify "droppable" values.
DenseSet<Value> deadVals;
+ // mark outgoing arguments to a public function LIVE. We also propagate
+ // liveness backward.
+ DenseSet<Value> liveVals;
// Maintains a list of Ops, values, branches, etc., slated for cleanup at the
// end of this pass.
RDVFinalCleanupList finalCleanupList;
- module->walk([&](Operation *op) {
+ module->walk<WalkOrder::PostOrder, BackwardIterator>([&](Operation *op) {
if (auto funcOp = dyn_cast<FunctionOpInterface>(op)) {
- processFuncOp(funcOp, module, la, deadVals, finalCleanupList);
+ processFuncOp(funcOp, module, la, deadVals, liveVals, finalCleanupList);
} else if (auto regionBranchOp = dyn_cast<RegionBranchOpInterface>(op)) {
- processRegionBranchOp(regionBranchOp, la, deadVals, finalCleanupList);
+ processRegionBranchOp(regionBranchOp, la, deadVals, liveVals,
+ finalCleanupList);
} else if (auto branchOp = dyn_cast<BranchOpInterface>(op)) {
- processBranchOp(branchOp, la, deadVals, finalCleanupList);
+ processBranchOp(branchOp, la, deadVals, liveVals, finalCleanupList);
} else if (op->hasTrait<::mlir::OpTrait::IsTerminator>()) {
// Nothing to do here because this is a terminator op and it should be
// honored with respect to its parent
} else if (isa<CallOpInterface>(op)) {
- // Nothing to do because this op is associated with a function op and gets
- // cleaned when the latter is cleaned.
+ processCallOp(cast<CallOpInterface>(op), module, la, deadVals, liveVals);
} else {
- processSimpleOp(op, la, deadVals, finalCleanupList);
+ processSimpleOp(op, la, deadVals, liveVals, finalCleanupList);
}
});
diff --git a/mlir/test/Transforms/remove-dead-values.mlir b/mlir/test/Transforms/remove-dead-values.mlir
index 56449469dc29f..ebb76a8835ceb 100644
--- a/mlir/test/Transforms/remove-dead-values.mlir
+++ b/mlir/test/Transforms/remove-dead-values.mlir
@@ -569,6 +569,24 @@ module @return_void_with_unused_argument {
call @fn_return_void_with_unused_argument(%arg0, %unused) : (i32, memref<4xi32>) -> ()
return %unused : memref<4xi32>
}
+
+ // the function signature is immutable because it is public.
+ func.func public @immutable_fn_with_unused_argument(%arg0: i32, %arg1: memref<4xf32>) -> () {
+ return
+ }
+
+ // CHECK-LABEL: func.func @main2
+ // CHECK: %[[MEM:.*]] = memref.alloc() : memref<4xf32>
+ // CHECK: %[[UNUSED:.*]] = arith.constant 0 : i32
+ // CHECK: call @immutable_fn_with_unused_argument(%[[UNUSED]], %[[MEM]]) : (i32, memref<4xf32>) -> ()
+ func.func @main2() -> () {
+ %one = arith.constant 1 : i32
+ %scalar = arith.addi %one, %one: i32
+ %mem = memref.alloc() : memref<4xf32>
+
+ call @immutable_fn_with_unused_argument(%scalar, %mem) : (i32, memref<4xf32>) -> ()
+ return
+ }
}
// -----
|
Contributor
Author
|
hi, @joker-eph |
joker-eph
reviewed
Oct 6, 2025
This diff also tries to propagate liveness recursively.
|
✅ With the latest revision this PR passed the C/C++ code formatter. |
navyxliu
changed the title
Contributor
Author
|
cc @victor-eds |
joker-eph
reviewed
Oct 20, 2025
Collaborator
joker-eph
left a comment
joker-eph
left a comment
There was a problem hiding this comment.
I think this should be fine, I have some minor comments inline, PTAL
also return LogicalResult and exits early when it encounters an error.
one optimization I made is that I don't clone function body. The function body migrates to the new private function. After that, I create wrapper body for the original function.
Collaborator
|
Just notice this got closed: not an issue anymore? |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
3 participants
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Problem
Liveness analysis is inter-procedural. If there are some unused arguments in a public function, they propagate to callers. From the perspective of RemoveDeadValues, the signature of a public function is immutable. It can't cope with this situation. One side, it deletes outgoing arguments, on the other side it keeps the function intact.
Solution
We deploy a pre-process pass called 'privatize-public-function'. It attempts to split interface and implementation if and only if
We split interface and implementation.
the original function is interface, the function body is just a forwarding call to the implementation. The new function is private as implementation. It derives the function body.
If IR has changed, we invalidate LivenessAnalysis and recompute for the following remove-dead-values.
Test plan
Alternatives
createDummyArgument replaces arguments with dummies. eg. If the type can create a value with zero initializer, such as 'T x{0}'. The downside of this method is that we may not construct trivial values for all types, in particular the aggregate types.
We add another DenseSet called 'liveSet'. The initial values are the arguments of public functions. It propagates liveness backward just like Liveness analysis.