[MLIR][NFC] Move test/Transforms/lower-affine.mlir -> test/Conversion

[bondhugula]

Summary

Move lower-affine.mlir from test/Transforms to
test/Conversion/AffineToStandard/. Other related NFC.

Signed-off-by: Uday Bondhugula <[e-mail]>

[ftynse]

Thanks for the cleanup!

mlir/docs/Passes.md

17

Nit: named maps and sets that are no longer in use (we may still have, e.g., memrefs with layout maps)

[bondhugula]

Address review comment

[bondhugula]

mlir/docs/Passes.md

17

Thanks!

mlir/docs/Passes.md

 # MLIR Passes
 
 This document describes the available MLIR passes and their contracts.
 
 [TOC]
 
-## Affine control lowering (`-lower-affine`)
+## Affine dialect lowering (`-lower-affine`)
 
-Convert operations related to affine control into a graph of blocks using
-operations from the standard dialect.
+Convert operations from the affine dialect into operations from the loop and
+standard dialects.
 
-Loop statements are converted to a subgraph of blocks (initialization, condition
-checking, subgraph of body blocks) with loop induction variable being passed as
-the block argument of the condition checking block. Conditional statements are
-converted to a subgraph of blocks (chain of condition checking with
-short-circuit logic, subgraphs of 'then' and 'else' body blocks). `affine.apply`
-operations are converted into sequences of primitive arithmetic operations that
-have the same effect, using operands of the `index` type. Consequently, named
-maps and sets may be removed from the module.
+`affine.for` operations are converted to `loop.for` operations that are free of
+certain structural restrictions (on their bounds and step). `affine.if` is
+similarly converted to the `loop.if` operation. `affine.apply` operations are
+converted into sequences of primitive arithmetic operations from the standard
+dialect that have the same effect, using operands of the `index` type.
+Consequently, named maps and sets thare are no longer in use may be removed from
+the module.
 
-For example, `%r = affine.apply (d0, d1)[s0] -> (d0 + 2*d1 + s0)(%d0, %d1)[%s0]`
+For example, `%r = affine.apply affine_map<(d0, d1)[s0] -> (d0 + 2*d1 +
+s0)>(%d0, %d1)[%s0]`
 can be converted into:
 
 ```mlir
 %d0 = <...>
 %d1 = <...>
 %s0 = <...>
 %0 = constant 2 : index
 %1 = muli %0, %d1

mlir/lib/Conversion/AffineToStandard/AffineToStandard.cpp

 /// Lowers If and For operations within a function into their lower level CFG
 /// equivalent blocks.
 std::unique_ptr<OpPassBase<FuncOp>> mlir::createLowerAffinePass() {
   return std::make_unique<LowerAffinePass>();
 }
 
 static PassRegistration<LowerAffinePass>
     pass("lower-affine",
-         "Lower If, For, AffineApply operations to primitive equivalents");
+         "Lower affine dialect operations to loop/standard dialect ones");