Commits on Sep 5, 2024

1. [mlir][Transforms] Dialect conversion: Make materializations optional (… …

   …#104668)
   
   This commit makes source/target/argument materializations (via the
   `TypeConverter` API) optional.
   
   By default (`ConversionConfig::buildMaterializations = true`), the
   dialect conversion infrastructure tries to legalize all unresolved
   materializations right after the main transformation process has
   succeeded. If at least one unresolved materialization fails to resolve,
   the dialect conversion fails. (With an error message such as `failed to
   legalize unresolved materialization ...`.) Automatic materializations
   through the `TypeConverter` API can now be deactivated. In that case,
   every unresolved materialization will show up as a
   `builtin.unrealized_conversion_cast` op in the output IR.
   
   There used to be a complex and error-prone analysis in the dialect
   conversion that predicted the future uses of unresolved
   materializations. Based on that logic, some casts (that were deemed to
   unnecessary) were folded. This analysis was needed because folding
   happened at a point of time when some IR changes (e.g., op replacements)
   had not materialized yet.
   
   This commit removes that analysis. Any folding of cast ops now happens
   after all other IR changes have been materialized and the uses can
   directly be queried from the IR. This simplifies the analysis
   significantly. And certain helper data structures such as
   `inverseMapping` are no longer needed for the analysis. The folding
   itself is done by `reconcileUnrealizedCasts` (which also exists as a
   standalone pass).
   
   After casts have been folded, the remaining casts are materialized
   through the `TypeConverter`, as usual. This last step can be deactivated
   in the `ConversionConfig`.
   
   `ConversionConfig::buildMaterializations = false` can be used to debug
   error messages such as `failed to legalize unresolved materialization
   ...`. (It is also useful in case automatic materializations are not
   needed.) The materializations that failed to resolve can then be seen as
   `builtin.unrealized_conversion_cast` ops in the resulting IR. (This is
   better than running with `-debug`, because `-debug` shows IR where some
   IR changes have not been materialized yet.)
   
   Note: This is a reupload of #104668, but with correct handling of cyclic unrealized_conversion_casts that may be generated by the dialect conversion.

   

   matthias-springer committed Sep 5, 2024
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2. Add regression test

   

   matthias-springer committed Sep 5, 2024
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