[Mlir-commits] [mlir] [SCF][Transform] Add support for scf.for in LoopFuseSibling op (PR #81495)

[Kunwar Grover]

================
@@ -970,3 +970,69 @@ scf::ForallOp mlir::fuseIndependentSiblingForallLoops(scf::ForallOp target,
 
   return fusedLoop;
 }
+
+scf::ForOp mlir::fuseIndependentSiblingForLoops(scf::ForOp target,
+                                                scf::ForOp source,
+                                                RewriterBase &rewriter) {
+  // Create fused init_args.
+  auto targetInitArgs = target.getInitArgs();
+  auto sourceInitArgs = source.getInitArgs();
+  SmallVector<Value> fusedInitArgs;
+  fusedInitArgs.reserve(targetInitArgs.size() + sourceInitArgs.size());
+  fusedInitArgs.append(sourceInitArgs.begin(), sourceInitArgs.end());
+  fusedInitArgs.append(targetInitArgs.begin(), targetInitArgs.end());
+
+  // Create a new scf::for op after the source loop.
+  rewriter.setInsertionPointAfter(source);
+  scf::ForOp fusedLoop = rewriter.create<scf::ForOp>(
+      source.getLoc(), source.getLowerBound(), source.getUpperBound(),
+      source.getStep(), fusedInitArgs);
+
+  SmallVector<Value> yieldResults;
+
+  // First merge source loop into the new (fused) for loop and then target loop.
+  rewriter.setInsertionPointToEnd(fusedLoop.getBody());
+  for (auto loopAndInitArgsBegin :
+       {std::pair(source, (unsigned int)0),
+        std::pair(target, source.getNumRegionIterArgs())}) {
+    auto origLoop = loopAndInitArgsBegin.first;
+    IRMapping mapping;
+
+    mapping.map(origLoop.getInductionVar(), fusedLoop.getInductionVar());
+    for (size_t i = 0; i < origLoop.getNumRegionIterArgs(); ++i) {
----------------
Groverkss wrote:

```suggestion
    for (size_t i = 0, e = origLoop.getNumRegionIterArgs(); i < e; ++i) {
```

https://llvm.org/docs/CodingStandards.html#don-t-evaluate-end-every-time-through-a-loop

https://github.com/llvm/llvm-project/pull/81495