[codegen 1.5] Implement ChannelToPortIoLoweringPass.

This pass transforms channel operations (Send/Receive) within a `ScheduledBlock` into either block ports or FIFO instantiations.

We also add support for zero-latency, skid, and single-flop buffering on streaming I/O channels. We port helper functions from codegen 1.0 to add registers and the necessary control logic for Ready/Valid/Data interfaces, though we make it simpler by constructing skid buffers as the combination of a zero-latency & register buffer.

Features not yet supported:
- Gating received data (for predicated or non-blocking receives)

PiperOrigin-RevId: 850524913

Author: ericastor

xls/codegen_v_1_5/BUILD

@@ -99,9 +99,62 @@ cc_library(
     hdrs = ["channel_to_port_io_lowering_pass.h"],
     deps = [
         ":block_conversion_pass",
+        "//xls/codegen:conversion_utils",
+        "//xls/codegen:ram_configuration",
+        "//xls/common:casts",
+        "//xls/common/status:ret_check",
+        "//xls/common/status:status_macros",
+        "//xls/ir",
+        "//xls/ir:bits",
+        "//xls/ir:channel",
+        "//xls/ir:node_util",
+        "//xls/ir:op",
+        "//xls/ir:register",
+        "//xls/ir:source_location",
+        "//xls/ir:value",
+        "//xls/ir:value_utils",
+        "//xls/passes:bdd_query_engine",
+        "//xls/passes:pass_base",
+        "//xls/public:function_builder",
+        "@com_google_absl//absl/algorithm:container",
+        "@com_google_absl//absl/base:core_headers",
+        "@com_google_absl//absl/container:btree",
+        "@com_google_absl//absl/container:flat_hash_map",
+        "@com_google_absl//absl/container:flat_hash_set",
+        "@com_google_absl//absl/container:inlined_vector",
+        "@com_google_absl//absl/log:check",
+        "@com_google_absl//absl/status",
+        "@com_google_absl//absl/status:statusor",
+        "@com_google_absl//absl/strings",
+        "@com_google_absl//absl/strings:str_format",
+        "@com_google_absl//absl/types:span",
+        "@cppitertools",
+    ],
+)
+
+cc_test(
+    name = "channel_to_port_io_lowering_pass_test",
+    srcs = ["channel_to_port_io_lowering_pass_test.cc"],
+    deps = [
+        ":block_conversion_pass",
+        ":channel_to_port_io_lowering_pass",
+        ":scheduled_block_conversion_pass",
+        "//xls/codegen:codegen_options",
+        "//xls/common:xls_gunit_main",
+        "//xls/common/status:matchers",
+        "//xls/common/status:status_macros",
         "//xls/ir",
+        "//xls/ir:bits",
+        "//xls/ir:channel",
+        "//xls/ir:channel_ops",
+        "//xls/ir:function_builder",
+        "//xls/ir:ir_matcher",
+        "//xls/ir:ir_test_base",
+        "//xls/ir:op",
+        "//xls/ir:value",
         "//xls/passes:pass_base",
         "@com_google_absl//absl/status:statusor",
+        "@googletest//:gtest",
     ],
 )