[Mlir-commits] [mlir] [MLIR][SCF] Canonicalize redundant scf.if from scf.while before region into after region (PR #169892)

[Ming Yan]

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@@ -3687,6 +3688,127 @@ LogicalResult scf::WhileOp::verify() {
 }
 
 namespace {
+/// Move a scf.if op that is directly before the scf.condition op in the while
+/// before region, and whose condition matches the condition of the
+/// scf.condition op, down into the while after region.
+///
+/// scf.while (..) : (...) -> ... {
+///  %additional_used_values = ...
+///  %cond = ...
+///  ...
+///  %res = scf.if %cond -> (...) {
+///    use(%additional_used_values)
+///    ... // then block
+///    scf.yield %then_value
+///  } else {
+///    scf.yield %else_value
+///  }
+///  scf.condition(%cond) %res, ...
+/// } do {
+/// ^bb0(%res_arg, ...):
+///    use(%res_arg)
+///    ...
+///
+/// becomes
+/// scf.while (..) : (...) -> ... {
+///  %additional_used_values = ...
+///  %cond = ...
+///  ...
+///  scf.condition(%cond) %else_value, ..., %additional_used_values
+/// } do {
+/// ^bb0(%res_arg ..., %additional_args): :
+///    use(%additional_args)
+///    ... // if then block
+///    use(%then_value)
+///    ...
+struct WhileMoveIfDown : public OpRewritePattern<scf::WhileOp> {
+  using OpRewritePattern<scf::WhileOp>::OpRewritePattern;
+
+  LogicalResult matchAndRewrite(scf::WhileOp op,
+                                PatternRewriter &rewriter) const override {
+    auto conditionOp =
+        cast<scf::ConditionOp>(op.getBeforeBody()->getTerminator());
+    auto ifOp = dyn_cast_or_null<scf::IfOp>(conditionOp->getPrevNode());
+
+    // Check that the ifOp is directly before the conditionOp and that it
+    // matches the condition of the conditionOp. Also ensure that the ifOp has
+    // no else block with content, as that would complicate the transformation.
+    // TODO: support else blocks with content.
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NexMing wrote:

Yes.

https://github.com/llvm/llvm-project/pull/169892