[all-commits] [llvm/llvm-project] e8f07c: [MLIR][SCF] Define `-scf-rotate-while` pass (#99850)

[Victor Perez via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: e8f07cdb57602d71f8960c0499765bcb000745c2
      https://github.com/llvm/llvm-project/commit/e8f07cdb57602d71f8960c0499765bcb000745c2
  Author: Victor Perez <victor.perez at codeplay.com>
  Date:   2024-07-30 (Tue, 30 Jul 2024)

  Changed paths:
    M mlir/include/mlir/Dialect/SCF/Transforms/Patterns.h
    M mlir/include/mlir/Dialect/SCF/Transforms/Transforms.h
    M mlir/lib/Dialect/SCF/Transforms/CMakeLists.txt
    A mlir/lib/Dialect/SCF/Transforms/RotateWhileLoop.cpp
    M mlir/test/Dialect/SCF/wrap-while-loop-in-zero-trip-check.mlir
    M mlir/test/lib/Dialect/SCF/TestSCFWrapInZeroTripCheck.cpp

  Log Message:
  -----------
  [MLIR][SCF] Define `-scf-rotate-while` pass (#99850)

Define SCF dialect patterns rotating `scf.while` loops leveraging
existing `mlir::scf::wrapWhileLoopInZeroTripCheck`. `forceCreateCheck`
is always `false` as the pattern would lead to an infinite recursion
otherwise.

This pattern rotates `scf.while` ops, mutating them from "while" loops to
"do-while" loops. A guard checking the condition for the first iteration
is inserted. Note this guard can be optimized away if the compiler can
prove the loop will be executed at least once.

Using this pattern, the following while loop:

```mlir
scf.while (%arg0 = %init) : (i32) -> i64 {
  %val = .., %arg0 : i64
  %cond = arith.cmpi .., %arg0 : i32
  scf.condition(%cond) %val : i64
} do {
^bb0(%arg1: i64):
  %next = .., %arg1 : i32
  scf.yield %next : i32
}
```

Can be transformed into:

``` mlir
%pre_val = .., %init : i64
%pre_cond = arith.cmpi .., %init : i32
scf.if %pre_cond -> i64 {
  %res = scf.while (%arg1 = %va0) : (i64) -> i64 {
    // Original after block
    %next = .., %arg1 : i32
    // Original before block
    %val = .., %next : i64
    %cond = arith.cmpi .., %next : i32
    scf.condition(%cond) %val : i64
  } do {
  ^bb0(%arg2: i64):
    %scf.yield %arg2 : i32
  }
  scf.yield %res : i64
} else {
  scf.yield %pre_val : i64
}
```

The test pass for `wrapWhileLoopInZeroTripCheck` has been modified to
use the new pattern when `forceCreateCheck=false`.

---------

Signed-off-by: Victor Perez <victor.perez at codeplay.com>



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