[mlir][scf] scf.while uplifting: optimize op matching (#88813)

Instead of iterating over potential induction var uses looking for
suitable `arith.addi`, try to trace it back from yield argument.

Author: Hardcode84

mlir/lib/Dialect/SCF/Transforms/UpliftWhileToFor.cpp

@@ -101,38 +101,30 @@ FailureOr<scf::ForOp> mlir::scf::upliftWhileToForLoop(RewriterBase &rewriter,
 
   Block *afterBody = loop.getAfterBody();
   scf::YieldOp afterTerm = loop.getYieldOp();
-  auto argNumber = inductionVar.getArgNumber();
-  auto afterTermIndArg = afterTerm.getResults()[argNumber];
+  unsigned argNumber = inductionVar.getArgNumber();
+  Value afterTermIndArg = afterTerm.getResults()[argNumber];
 
-  auto inductionVarAfter = afterBody->getArgument(argNumber);
-
-  Value step;
+  Value inductionVarAfter = afterBody->getArgument(argNumber);
 
   // Find suitable `addi` op inside `after` block, one of the args must be an
   // Induction var passed from `before` block and second arg must be defined
   // outside of the loop and will be considered step value.
   // TODO: Add `subi` support?
-  for (auto &use : inductionVarAfter.getUses()) {
-    auto owner = dyn_cast<arith::AddIOp>(use.getOwner());
-    if (!owner)
-      continue;
-
-    auto other =
-        (inductionVarAfter == owner.getLhs() ? owner.getRhs() : owner.getLhs());
-    if (!dom.properlyDominates(other, loop))
-      continue;
-
-    if (afterTermIndArg != owner.getResult())
-      continue;
+  auto addOp = afterTermIndArg.getDefiningOp<arith::AddIOp>();
+  if (!addOp)
+    return rewriter.notifyMatchFailure(loop, "Didn't found suitable 'addi' op");
 
-    step = other;
-    break;
+  Value step;
+  if (addOp.getLhs() == inductionVarAfter) {
+    step = addOp.getRhs();
+  } else if (addOp.getRhs() == inductionVarAfter) {
+    step = addOp.getLhs();
   }
 
-  if (!step)
-    return rewriter.notifyMatchFailure(loop, "Didn't found suitable 'addi' op");
+  if (!step || !dom.properlyDominates(step, loop))
+    return rewriter.notifyMatchFailure(loop, "Invalid 'addi' form");
 
-  auto lb = loop.getInits()[argNumber];
+  Value lb = loop.getInits()[argNumber];
 
   assert(lb.getType().isIntOrIndex());
   assert(lb.getType() == ub.getType());