[CIR] Add live object analysis pass

Add a backward dataflow analysis that computes object liveness at each
program point using points-to information. The analysis determines when
objects are last used, supporting control flow constructs including
loops, gotos, and region-based operations. Includes diagnostic pass
for emitting last-use remarks and cir-opt integration.

Co-authored-by: Tommy McMichen <tommymcmichen@fb.com>

Author: bcardosolopes

clang/include/clang/CIR/Dialect/Passes.h

@@ -35,6 +35,7 @@ std::unique_ptr<Pass> createLoweringPreparePass(clang::ASTContext *astCtx);
 std::unique_ptr<Pass> createIdiomRecognizerPass();
 std::unique_ptr<Pass> createIdiomRecognizerPass(clang::ASTContext *astCtx);
 std::unique_ptr<Pass> createPointsToDiagnosticPass();
+std::unique_ptr<Pass> createLiveObjectDiagnosticPass();
 std::unique_ptr<Pass> createLibOptPass();
 std::unique_ptr<Pass> createLibOptPass(clang::ASTContext *astCtx);
 std::unique_ptr<Pass> createFlattenCFGPass();

clang/include/clang/CIR/Dialect/Passes.td

@@ -156,6 +156,15 @@ def PointsToDiagnostic : Pass<"cir-points-to-diagnostics"> {
   let dependentDialects = ["cir::CIRDialect"];
 }
 
+def LiveObjectDiagnostic : Pass<"cir-live-object-diagnostics"> {
+  let summary = "Dump live-object information";
+  let description = [{
+    Dump live-object information for all reads/writes in the function.
+  }];
+  let constructor = "mlir::createLiveObjectDiagnosticPass()";
+  let dependentDialects = ["cir::CIRDialect"];
+}
+
 def IdiomRecognizer : Pass<"cir-idiom-recognizer"> {
   let summary = "Raise calls to C/C++ libraries to CIR operations";
   let description = [{

clang/lib/CIR/Dialect/Transforms/CMakeLists.txt

@@ -16,6 +16,7 @@ add_clang_library(MLIRCIRTransforms
   CallConvLowering.cpp
   HoistAllocas.cpp
   PointsToAnalysis.cpp
+  LiveObjectAnalysis.cpp
   StdLibStatistics.cpp
 
   DEPENDS