[mlir] Implement pass utils for 1:N type conversions.

The current dialect conversion does not support 1:N type conversions.
This commit implements a (poor-man's) dialect conversion pass that does
just that. To keep the pass independent of the "real" dialect conversion
infrastructure, it provides a specialization of the TypeConverter class
that allows for N:1 target materializations, a specialization of the
RewritePattern and PatternRewriter classes that automatically add
appropriate unrealized casts supporting 1:N type conversions and provide
converted operands for implementing subclasses, and a conversion driver
that applies the provided patterns and replaces the unrealized casts
that haven't folded away with user-provided materializations.

The current pass is powerful enough to express many existing manual
solutions for 1:N type conversions or extend transforms that previously
didn't support them, out of which this patch implements call graph type
decomposition (which is currently implemented with a ValueDecomposer
that is only used there).

The goal of this pass is to illustrate the effect that 1:N type
conversions could have, gain experience in how patterns should be
written that achieve that effect, and get feedback on how the APIs of
the dialect conversion should be extended or changed to support such
patterns. The hope is that the "real" dialect conversion eventually
supports such patterns, at which point, this pass could be removed
again.

Reviewed By: springerm

Differential Revision: https://reviews.llvm.org/D144469

2 files changed, 3 insertions, 0 deletions

diff --git a/mlir/tools/mlir-opt/CMakeLists.txt b/mlir/tools/mlir-opt/CMakeLists.txt
index f84fbe631cf1..c43056906da8 100644
--- a/mlir/tools/mlir-opt/CMakeLists.txt
+++ b/mlir/tools/mlir-opt/CMakeLists.txt
@@ -33,6 +33,7 @@ if(MLIR_INCLUDE_TESTS)
     MLIRTestDialect
     MLIRTestDynDialect
     MLIRTestIR
+    MLIRTestOneToNTypeConversionPass
     MLIRTestPass
     MLIRTestPDLL
     MLIRTestReducer
diff --git a/mlir/tools/mlir-opt/mlir-opt.cpp b/mlir/tools/mlir-opt/mlir-opt.cpp
index e7ca06b4bef9..855c6a6e0f28 100644
--- a/mlir/tools/mlir-opt/mlir-opt.cpp
+++ b/mlir/tools/mlir-opt/mlir-opt.cpp
@@ -107,6 +107,7 @@ void registerTestMathAlgebraicSimplificationPass();
 void registerTestMathPolynomialApproximationPass();
 void registerTestMemRefDependenceCheck();
 void registerTestMemRefStrideCalculation();
+void registerTestOneToNTypeConversionPass();
 void registerTestOpaqueLoc();
 void registerTestPadFusion();
 void registerTestPDLByteCodePass();
@@ -218,6 +219,7 @@ void registerTestPasses() {
   mlir::test::registerTestMathPolynomialApproximationPass();
   mlir::test::registerTestMemRefDependenceCheck();
   mlir::test::registerTestMemRefStrideCalculation();
+  mlir::test::registerTestOneToNTypeConversionPass();
   mlir::test::registerTestOpaqueLoc();
   mlir::test::registerTestPadFusion();
   mlir::test::registerTestPDLByteCodePass();