[mlir][SideEffects] Replace HasNoSideEffect with the memory effect interfaces.

HasNoSideEffect can now be implemented using the MemoryEffectInterface, removing the need to check multiple things for the same information. This also removes an easy foot-gun for users as 'Operation::hasNoSideEffect' would ignore operations that dynamically, or recursively, have no side effects. This also leads to an immediate improvement in some of the existing users, such as DCE, now that they have access to more information.

Differential Revision: https://reviews.llvm.org/D76036

6 files changed, 34 insertions, 27 deletions

diff --git a/mlir/lib/Transforms/CSE.cpp b/mlir/lib/Transforms/CSE.cpp
index 3a76594..42ba715 100644
--- a/mlir/lib/Transforms/CSE.cpp
+++ b/mlir/lib/Transforms/CSE.cpp
@@ -127,6 +127,13 @@ LogicalResult CSE::simplifyOperation(ScopedMapTy &knownValues, Operation *op) {
   if (op->isKnownTerminator())
     return failure();
 
+  // If the operation is already trivially dead just add it to the erase list.
+  if (isOpTriviallyDead(op)) {
+    opsToErase.push_back(op);
+    ++numDCE;
+    return success();
+  }
+
   // Don't simplify operations with nested blocks. We don't currently model
   // equality comparisons correctly among other things. It is also unclear
   // whether we would want to CSE such operations.
@@ -135,16 +142,9 @@ LogicalResult CSE::simplifyOperation(ScopedMapTy &knownValues, Operation *op) {
 
   // TODO(riverriddle) We currently only eliminate non side-effecting
   // operations.
-  if (!op->hasNoSideEffect())
+  if (!MemoryEffectOpInterface::hasNoEffect(op))
     return failure();
 
-  // If the operation is already trivially dead just add it to the erase list.
-  if (op->use_empty()) {
-    opsToErase.push_back(op);
-    ++numDCE;
-    return success();
-  }
-
   // Look for an existing definition for the operation.
   if (auto *existing = knownValues.lookup(op)) {
     // If we find one then replace all uses of the current operation with the
diff --git a/mlir/lib/Transforms/LoopInvariantCodeMotion.cpp b/mlir/lib/Transforms/LoopInvariantCodeMotion.cpp
index a452e33..7300948 100644
--- a/mlir/lib/Transforms/LoopInvariantCodeMotion.cpp
+++ b/mlir/lib/Transforms/LoopInvariantCodeMotion.cpp
@@ -49,16 +49,18 @@ static bool canBeHoisted(Operation *op,
   if (auto memInterface = dyn_cast<MemoryEffectOpInterface>(op)) {
     if (!memInterface.hasNoEffect())
       return false;
-  } else if (!op->hasNoSideEffect() &&
-             !op->hasTrait<OpTrait::HasRecursiveSideEffects>()) {
+    // If the operation doesn't have side effects and it doesn't recursively
+    // have side effects, it can always be hoisted.
+    if (!op->hasTrait<OpTrait::HasRecursiveSideEffects>())
+      return true;
+
+    // Otherwise, if the operation doesn't provide the memory effect interface
+    // and it doesn't have recursive side effects we treat it conservatively as
+    // side-effecting.
+  } else if (!op->hasTrait<OpTrait::HasRecursiveSideEffects>()) {
     return false;
   }
 
-  // If the operation doesn't have side effects and it doesn't recursively
-  // have side effects, it can always be hoisted.
-  if (!op->hasTrait<OpTrait::HasRecursiveSideEffects>())
-    return true;
-
   // Recurse into the regions for this op and check whether the contained ops
   // can be hoisted.
   for (auto &region : op->getRegions()) {
diff --git a/mlir/lib/Transforms/Utils/FoldUtils.cpp b/mlir/lib/Transforms/Utils/FoldUtils.cpp
index f374d38..66535ec 100644
--- a/mlir/lib/Transforms/Utils/FoldUtils.cpp
+++ b/mlir/lib/Transforms/Utils/FoldUtils.cpp
@@ -126,6 +126,12 @@ void OperationFolder::notifyRemoval(Operation *op) {
   referencedDialects.erase(it);
 }
 
+/// Clear out any constants cached inside of the folder.
+void OperationFolder::clear() {
+  foldScopes.clear();
+  referencedDialects.clear();
+}
+
 /// Tries to perform folding on the given `op`. If successful, populates
 /// `results` with the results of the folding.
 LogicalResult OperationFolder::tryToFold(
diff --git a/mlir/lib/Transforms/Utils/GreedyPatternRewriteDriver.cpp b/mlir/lib/Transforms/Utils/GreedyPatternRewriteDriver.cpp
index f9a9be5..e40a4d9 100644
--- a/mlir/lib/Transforms/Utils/GreedyPatternRewriteDriver.cpp
+++ b/mlir/lib/Transforms/Utils/GreedyPatternRewriteDriver.cpp
@@ -10,9 +10,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "mlir/Dialect/StandardOps/IR/Ops.h"
-#include "mlir/IR/Builders.h"
 #include "mlir/IR/PatternMatch.h"
+#include "mlir/Interfaces/SideEffects.h"
 #include "mlir/Transforms/FoldUtils.h"
 #include "mlir/Transforms/RegionUtils.h"
 #include "llvm/ADT/DenseMap.h"
@@ -162,11 +161,8 @@ bool GreedyPatternRewriteDriver::simplify(MutableArrayRef<Region> regions,
       if (op == nullptr)
         continue;
 
-      // If the operation has no side effects, and no users, then it is
-      // trivially dead - remove it.
-      if (op->isKnownNonTerminator() && op->hasNoSideEffect() &&
-          op->use_empty()) {
-        // Be careful to update bookkeeping.
+      // If the operation is trivially dead - remove it.
+      if (isOpTriviallyDead(op)) {
         notifyOperationRemoved(op);
         op->erase();
         continue;
@@ -204,7 +200,10 @@ bool GreedyPatternRewriteDriver::simplify(MutableArrayRef<Region> regions,
 
     // After applying patterns, make sure that the CFG of each of the regions is
     // kept up to date.
-    changed |= succeeded(simplifyRegions(regions));
+    if (succeeded(simplifyRegions(regions))) {
+      folder.clear();
+      changed = true;
+    }
   } while (changed && ++i < maxIterations);
   // Whether the rewrite converges, i.e. wasn't changed in the last iteration.
   return !changed;
diff --git a/mlir/lib/Transforms/Utils/LoopUtils.cpp b/mlir/lib/Transforms/Utils/LoopUtils.cpp
index a02c71a..7095e55 100644
--- a/mlir/lib/Transforms/Utils/LoopUtils.cpp
+++ b/mlir/lib/Transforms/Utils/LoopUtils.cpp
@@ -887,7 +887,7 @@ static LogicalResult hoistOpsBetween(loop::ForOp outer, loop::ForOp inner) {
     }
     // Skip if op has side effects.
     // TODO(ntv): loads to immutable memory regions are ok.
-    if (!op.hasNoSideEffect()) {
+    if (!MemoryEffectOpInterface::hasNoEffect(&op)) {
       status = failure();
       continue;
     }
diff --git a/mlir/lib/Transforms/Utils/RegionUtils.cpp b/mlir/lib/Transforms/Utils/RegionUtils.cpp
index 78bb609b..162091c 100644
--- a/mlir/lib/Transforms/Utils/RegionUtils.cpp
+++ b/mlir/lib/Transforms/Utils/RegionUtils.cpp
@@ -12,6 +12,7 @@
 #include "mlir/IR/RegionGraphTraits.h"
 #include "mlir/IR/Value.h"
 #include "mlir/Interfaces/ControlFlowInterfaces.h"
+#include "mlir/Interfaces/SideEffects.h"
 
 #include "llvm/ADT/DepthFirstIterator.h"
 #include "llvm/ADT/PostOrderIterator.h"
@@ -196,9 +197,8 @@ static bool isOpIntrinsicallyLive(Operation *op) {
   if (!op->isKnownNonTerminator())
     return true;
   // If the op has a side effect, we treat it as live.
-  if (!op->hasNoSideEffect())
-    return true;
-  return false;
+  // TODO: Properly handle region side effects.
+  return !MemoryEffectOpInterface::hasNoEffect(op) || op->getNumRegions() != 0;
 }
 
 static void propagateLiveness(Region &region, LiveMap &liveMap);