mlir: share the CPU lowering front-end between the LLVM and C targets

src/xtc/backends/mlir/MlirTarget/MlirCTarget.py

@@ -32,6 +32,7 @@
 from xtc.itf.graph import Graph
 
 from .MlirTarget import MlirTarget
+from .cpu_lowering import cpu_frontend_lowering
 from ..MlirConfig import MlirConfig
 from ..MlirProgram import RawMlirProgram
 
@@ -265,31 +266,10 @@ def __init__(
         self._mlir_program = mlir_program
 
     def _lowering_pipeline(self) -> list[str]:
-        pipeline = [
-            "canonicalize",
-            "cse",
-            "sccp",
-        ]
-        if "sdist" in self._mlir_program.mlir_extensions:
-            pipeline += [
-                "sdist-lower-distribution",
-                "convert-sdist-to-std",
-                "cse",
-                "canonicalize",
-                "convert-sdist-utils-to-std",
-            ]
-        pipeline += [
-            # From complex control to the soup of basic blocks
-            "expand-strided-metadata",
-            "convert-linalg-to-loops",
-            "lower-affine",
-            "convert-vector-to-scf{full-unroll=true}",
-            "scf-forall-to-parallel",
-            "convert-scf-to-openmp",
-            "canonicalize",
-            "cse",
-            "sccp",
-            # "convert-scf-to-cf",
+        return cpu_frontend_lowering(
+            self._mlir_program.mlir_extensions, uplift_fma=False
+        ) + [
+            # convert-scf-to-cf is intentionally skipped: the C emitter keeps scf
             "canonicalize",
             "cse",
             "sccp",
@@ -299,7 +279,6 @@ def _lowering_pipeline(self) -> list[str]:
             "cse",
             "sccp",
         ]
-        return pipeline
 
     def run(self) -> None:
         pm = PassManager(context=self._mlir_program.mlir_context)

src/xtc/backends/mlir/MlirTarget/MlirLLVMTarget.py

@@ -33,6 +33,7 @@
 from xtc.itf.graph import Graph
 
 from .MlirTarget import MlirTarget
+from .cpu_lowering import cpu_frontend_lowering
 from ..MlirConfig import MlirConfig
 from ..MlirProgram import RawMlirProgram
 
@@ -277,32 +278,9 @@ def __init__(
         self._mlir_program = mlir_program
 
     def _lowering_pipeline(self) -> list[str]:
-        pipeline = [
-            "canonicalize",
-            "cse",
-            "sccp",
-        ]
-        if "sdist" in self._mlir_program.mlir_extensions:
-            pipeline += [
-                "sdist-lower-distribution",
-                "convert-sdist-to-std",
-                "cse",
-                "canonicalize",
-                "convert-sdist-utils-to-std",
-            ]
-        pipeline += [
-            # From complex control to the soup of basic blocks
-            "math-uplift-to-fma",
-            "expand-strided-metadata",
-            "convert-linalg-to-loops",
-            "lower-affine",
-            "func.func(lower-vector-mask)",
-            "convert-vector-to-scf{full-unroll=true}",
-            "scf-forall-to-parallel",
-            "convert-scf-to-openmp",
-            "canonicalize",
-            "cse",
-            "sccp",
+        return cpu_frontend_lowering(
+            self._mlir_program.mlir_extensions, uplift_fma=True
+        ) + [
             "convert-scf-to-cf",
             "canonicalize",
             "cse",
@@ -330,7 +308,6 @@ def _lowering_pipeline(self) -> list[str]:
             "cse",
             "sccp",
         ]
-        return pipeline
 
     def run(self) -> None:
         pm = PassManager(context=self._mlir_program.mlir_context)

src/xtc/backends/mlir/MlirTarget/cpu_lowering.py

@@ -0,0 +1,43 @@
+#
+# SPDX-License-Identifier: BSD-3-Clause
+# Copyright (c) 2024-2026 The XTC Project Authors
+#
+
+
+def cpu_frontend_lowering(mlir_extensions: list[str], *, uplift_fma: bool) -> list[str]:
+    """Shared CPU lowering prefix for the LLVM and C targets.
+
+    Lowers linalg/vector down to scf, before the target-specific transformations.
+
+    Args:
+        mlir_extensions: extensions required by the program
+        uplift_fma: whether to uplift ``mul``+``add`` to ``fma``
+
+    Returns:
+        The ordered list of pass names for the shared front-end lowering.
+    """
+    pipeline = ["canonicalize", "cse", "sccp"]
+    if "sdist" in mlir_extensions:
+        pipeline += [
+            "sdist-lower-distribution",
+            "convert-sdist-to-std",
+            "cse",
+            "canonicalize",
+            "convert-sdist-utils-to-std",
+        ]
+    if uplift_fma:
+        pipeline.append("math-uplift-to-fma")
+    pipeline += [
+        # From complex control to the soup of basic blocks
+        "expand-strided-metadata",
+        "convert-linalg-to-loops",
+        "lower-affine",
+        "func.func(lower-vector-mask)",
+        "convert-vector-to-scf{full-unroll=true}",
+        "scf-forall-to-parallel",
+        "convert-scf-to-openmp",
+        "canonicalize",
+        "cse",
+        "sccp",
+    ]
+    return pipeline