[XLA] Add HLO alias analysis.

Add HloAliasAnalysis which identifies aliasing of buffers in the HLO graph. This analysis is module-scoped and will eventually replace the computation-scoped TuplePointsToAnalysis. Currently the analysis is unused, but later CLs will incrementally replace TuplePointsToAnalysis with HloAliasAnalysis (or potentially HloDataflowAnalysis).

This CL also includes a small change to HloDataflowAnalysis. When ssa_form is true, only while instructions (which update inplace) define phi values. Previously, subcomputations called from multiple kCall instructions would also define phi values. Effectively this is an inconsequential change because we always flatten the callgraph eliminating multiple callsites for the same subcomputation.

PiperOrigin-RevId: 158537805

tensorflow/compiler/xla/service/BUILD

@@ -1178,6 +1178,49 @@ cc_test(
  ],
 )
 
+cc_library(
+ name = "hlo_alias_analysis",
+ srcs = [
+ "hlo_alias_analysis.cc",
+ ],
+ hdrs = [
+ "hlo_alias_analysis.h",
+ ],
+ deps = [
+ ":call_graph",
+ ":hlo",
+ ":hlo_dataflow_analysis",
+ ":logical_buffer",
+ "//tensorflow/compiler/xla:shape_tree",
+ "//tensorflow/compiler/xla:shape_util",
+ "//tensorflow/compiler/xla:statusor",
+ "//tensorflow/compiler/xla:types",
+ "//tensorflow/compiler/xla:util",
+ "//tensorflow/compiler/xla:xla_data_proto",
+ "//tensorflow/core:lib",
+ ],
+)
+
+cc_test(
+ name = "hlo_alias_analysis_test",
+ srcs = ["hlo_alias_analysis_test.cc"],
+ deps = [
+ ":hlo",
+ ":hlo_alias_analysis",
+ ":hlo_matchers",
+ ":instruction_fusion",
+ "//tensorflow/compiler/xla:literal_util",
+ "//tensorflow/compiler/xla:shape_util",
+ "//tensorflow/compiler/xla:test",
+ "//tensorflow/compiler/xla:test_helpers",
+ "//tensorflow/compiler/xla:xla_data_proto",
+ "//tensorflow/compiler/xla/tests:hlo_test_base",
+ "//tensorflow/core:lib",
+ "//tensorflow/core:test",
+ "//tensorflow/core:test_main",
+ ],
+)
+
 cc_library(
  name = "tuple_points_to_analysis",
  srcs = [