[Mlir-commits] [mlir] [mlir][scf] Fold away `scf.for` iter args cycles (PR #173436)

[Matthias Springer]

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@@ -1236,12 +1236,101 @@ struct ForOpTensorCastFolder : public OpRewritePattern<ForOp> {
   }
 };
 
+/// Rewriting pattern that folds away cycles in the yield of a scf.for op.
+///
+/// ```
+/// %res:2 = scf.for ... iter_args(%arg0 = %init, %arg1 = %init) {
+///   ...
+///   use %arg0, %arg1
+///   scf.yield %arg1, %arg0
+/// }
+/// return %res#0, %res#1
+/// ```
+///
+/// folds into:
+///
+/// ```
+/// scf.for ... iter_args() {
+///   ...
+///   use %init, %init
+///   scf.yield
+/// }
+/// return %init, %init
+/// ```
+struct ForOpYieldCyclesFolder : public OpRewritePattern<ForOp> {
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matthias-springer wrote:

I was hoping that the pattern would get much simpler, but looks like it may not be possible to simplify much more. Thanks.

https://github.com/llvm/llvm-project/pull/173436