[BACKEND] Optimize code style in rewrite-tensor-pointer and add more tests (triton-lang#4724)

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---

Hello, maintainers and reviewers!

While reading the
[RewriteTensorPointer.cpp](https://github.com/triton-lang/triton/blob/main/lib/Dialect/Triton/Transforms/RewriteTensorPointer.cpp)
pass, I noticed that the current implementation to be somewhat redundant
and the test is hard to understand, so I submitted this PR.

PR description：

- Use `llvm::make_early_inc_range` to ensure no issues arise during
visiting ops, instead of making a copy

```mlir
    for (auto &region : op->getRegions()) {
      for (auto &block : region) {
        SmallVector<Operation *> blockCopy;
        for (auto &nestedOp : block)
          blockCopy.push_back(&nestedOp);
        for (auto &nestedOp : blockCopy) {
          if (auto newOp = rewriteOp(nestedOp, eraser))

-> 

    for (Region &region : op->getRegions()) {
      for (Block &block : region) {
        for (Operation &nestedOp : llvm::make_early_inc_range(block)) {
          if (auto newOp = rewriteOp(&nestedOp, eraser)) {
            visitOperation(newOp, eraser);
          }
```

- Return directly from the parameter instead of constructing a new
SmallVector.

```mlir
  static SmallVector<Value>
  generateNewOperands(const SmallVector<Value> &oldOperands, unsigned index,
                      const SmallVector<Value> &newValues) {

->

  static void generateNewOperands(SmallVector<Value> &oldOperands,
                                  unsigned index, ArrayRef<Value> newValues) {
```


- delete some dead code

-  add detailed tests.

see test/Triton/rewrite-tensor-pointer.mlir

Co-authored-by: Keren Zhou <[email protected]>

Author: tfruan2000

lib/Dialect/Triton/Transforms/RewriteTensorPointer.cpp

@@ -1,7 +1,9 @@
 #include <memory>
 #include <stack>
 
+#include "mlir/Dialect/ControlFlow/IR/ControlFlow.h"
 #include "mlir/Dialect/ControlFlow/IR/ControlFlowOps.h"
+#include "mlir/Dialect/SCF/IR/SCF.h"
 #include "mlir/Pass/Pass.h"
 #include "mlir/Support/LLVM.h"
 #include "triton/Analysis/Utility.h"
@@ -171,10 +173,7 @@ struct RewritedInfo {
     auto otherTensorType = RankedTensorType::get(tensorShape, elementType);
 
     // Set zero padding value
-    TypedAttr attr =
-        elementType.isIntOrIndex()
-            ? cast<TypedAttr>(builder.getIntegerAttr(elementType, 0))
-            : cast<TypedAttr>(builder.getFloatAttr(elementType, 0));
+    TypedAttr attr = builder.getZeroAttr(elementType);
 
     // Float NaN padding case
     if (padding.value() == triton::PaddingOption::PAD_NAN) {
@@ -209,18 +208,20 @@ class RewriteTensorPointerPass
                        });
   }
 
-  static SmallVector<Value>
-  generateNewOperands(const SmallVector<Value> &oldOperands, unsigned index,
-                      const SmallVector<Value> &newValues) {
-    assert(index < oldOperands.size());
-    SmallVector<Value> newOperands;
-    for (int i = 0; i < index; ++i)
-      newOperands.push_back(oldOperands[i]);
-    for (auto value : newValues)
-      newOperands.push_back(value);
-    for (auto i = index + 1; i < oldOperands.size(); ++i)
-      newOperands.push_back(oldOperands[i]);
-    return newOperands;
+  static void generateNewOperands(SmallVector<Value> &oldOperands,
+                                  unsigned index, ArrayRef<Value> newValues) {
+    size_t size = oldOperands.size();
+    assert(index < size);
+    SmallVector<Value> operands = oldOperands;
+    oldOperands.reserve(size - 1 + newValues.size());
+    oldOperands.clear();
+    if (index != 0) {
+      oldOperands.append(operands.begin(), operands.begin() + index);
+    }
+    oldOperands.append(newValues.begin(), newValues.end());
+    if (index != size - 1) {
+      oldOperands.append(operands.begin() + index + 1, operands.end());
+    }
   }
 
   Operation *rewriteMakeTensorPtrOp(OpBuilder &builder,
@@ -358,7 +359,7 @@ class RewriteTensorPointerPass
     }
     auto rematerialize = [&](Block *block) {
       for (Operation &opInIf : block->getOperations()) {
-        auto newOp = builder.clone(opInIf, mapping);
+        builder.clone(opInIf, mapping);
       }
     };
     builder.setInsertionPointToStart(newOp.thenBlock());
@@ -403,8 +404,7 @@ class RewriteTensorPointerPass
       // Expand the tensor pointer into offsets
       assert(rewritedInfo.count(newIterOperands[i]));
       auto info = rewritedInfo[newIterOperands[i]];
-      newIterOperands =
-          generateNewOperands(newIterOperands, i, info.getOffsets());
+      generateNewOperands(newIterOperands, i, info.getOffsets());
       i += info.length() - 1;
       size += info.length() - 1;
     }
@@ -439,9 +439,7 @@ class RewriteTensorPointerPass
     // Clone body
     builder.setInsertionPointToStart(newForOp.getBody());
     for (auto &opInFor : *op.getBody()) {
-      auto *newOp = builder.clone(opInFor, mapping);
-      for (unsigned i = 0; i < opInFor.getNumResults(); ++i)
-        mapping.map(opInFor.getResult(i), newOp->getResult(i));
+      builder.clone(opInFor, mapping);
     }
 
     // Replace later usages
@@ -476,7 +474,7 @@ class RewriteTensorPointerPass
 
       assert(rewritedInfo.count(newOperands[i]));
       auto info = rewritedInfo[newOperands[i]];
-      newOperands = generateNewOperands(newOperands, i, info.getOffsets());
+      generateNewOperands(newOperands, i, info.getOffsets());
       i += info.length() - 1;
       size += info.length() - 1;
     }
@@ -492,15 +490,13 @@ class RewriteTensorPointerPass
     // Rewrite `make_tensor_ptr` and `advance` and make a tensor of pointers
     // Rewriting functions return the next operation to visit, if there is no
     // next one, simply return `nullptr`
-    std::pair<Value, RewritedInfo> rewrited;
     if (auto makeTensorPtrOp = dyn_cast<triton::MakeTensorPtrOp>(op)) {
       return rewriteMakeTensorPtrOp(builder, makeTensorPtrOp, eraser);
     } else if (auto advanceOp = dyn_cast<triton::AdvanceOp>(op)) {
       return rewriteAdvanceOp(builder, advanceOp, eraser);
     } else if (isa<triton::LoadOp>(op) || isa<triton::StoreOp>(op)) {
       return rewriteLoadStoreOp(builder, op, eraser);
-    } else if (op->getDialect()->getNamespace() == "scf" ||
-               op->getDialect()->getNamespace() == "cf") {
+    } else if (isa<scf::SCFDialect, cf::ControlFlowDialect>(op->getDialect())) {
       if (auto ifOp = dyn_cast<scf::IfOp>(op)) {
         return rewriteIfOp(builder, ifOp, eraser);
       }
@@ -524,18 +520,12 @@ class RewriteTensorPointerPass
   }
 
   void visitOperation(Operation *op, std::stack<Operation *> &eraser) {
-    for (auto &region : op->getRegions()) {
-      for (auto &block : region) {
-        // We need an extra copy because erasing operations may break the
-        // iterator behavior
-        SmallVector<Operation *> blockCopy;
-        for (auto &nestedOp : block)
-          blockCopy.push_back(&nestedOp);
-
-        // Rewrite and recursively visit
-        for (auto &nestedOp : blockCopy) {
-          if (auto newOp = rewriteOp(nestedOp, eraser))
+    for (Region &region : op->getRegions()) {
+      for (Block &block : region) {
+        for (Operation &nestedOp : llvm::make_early_inc_range(block)) {
+          if (auto newOp = rewriteOp(&nestedOp, eraser)) {
             visitOperation(newOp, eraser);
+          }
         }
       }
     }