[flang] Erase fir.local ops before lowering fir to llvm (#143687)

`fir.local` ops are not supposed to have any uses at this point (i.e.
during lowering to LLVM). In case of serialization, the
`fir.do_concurrent` users are expected to have been lowered to
`fir.do_loop` nests. In case of parallelization, the `fir.do_concurrent`
users are expected to have been lowered to the target parallel model
(e.g. OpenMP).

This hopefully resolved a build issue introduced by
https://github.com/llvm/llvm-project/pull/142567 (see for example:
https://lab.llvm.org/buildbot/#/builders/199/builds/4009).

flang/lib/Optimizer/CodeGen/CodeGen.cpp

@@ -3294,6 +3294,30 @@ struct LoadOpConversion : public fir::FIROpConversion<fir::LoadOp> {
   }
 };
 
+struct LocalitySpecifierOpConversion
+    : public fir::FIROpConversion<fir::LocalitySpecifierOp> {
+  using FIROpConversion::FIROpConversion;
+  llvm::LogicalResult
+  matchAndRewrite(fir::LocalitySpecifierOp localizer, OpAdaptor adaptor,
+                  mlir::ConversionPatternRewriter &rewriter) const override {
+#ifdef EXPENSIVE_CHECKS
+    auto uses = mlir::SymbolTable::getSymbolUses(
+        localizer, localizer->getParentOfType<mlir::ModuleOp>());
+
+    // `fir.local` ops are not supposed to have any uses at this point (i.e.
+    // during lowering to LLVM). In case of serialization, the
+    // `fir.do_concurrent` users are expected to have been lowered to
+    // `fir.do_loop` nests. In case of parallelization, the `fir.do_concurrent`
+    // users are expected to have been lowered to the target parallel model
+    // (e.g. OpenMP).
+    assert(uses && uses->empty());
+#endif
+
+    rewriter.eraseOp(localizer);
+    return mlir::success();
+  }
+};
+
 /// Lower `fir.no_reassoc` to LLVM IR dialect.
 /// TODO: how do we want to enforce this in LLVM-IR? Can we manipulate the fast
 /// math flags?
@@ -4249,15 +4273,15 @@ void fir::populateFIRToLLVMConversionPatterns(
       FieldIndexOpConversion, FirEndOpConversion, FreeMemOpConversion,
       GlobalLenOpConversion, GlobalOpConversion, InsertOnRangeOpConversion,
       IsPresentOpConversion, LenParamIndexOpConversion, LoadOpConversion,
-      MulcOpConversion, NegcOpConversion, NoReassocOpConversion,
-      SelectCaseOpConversion, SelectOpConversion, SelectRankOpConversion,
-      SelectTypeOpConversion, ShapeOpConversion, ShapeShiftOpConversion,
-      ShiftOpConversion, SliceOpConversion, StoreOpConversion,
-      StringLitOpConversion, SubcOpConversion, TypeDescOpConversion,
-      TypeInfoOpConversion, UnboxCharOpConversion, UnboxProcOpConversion,
-      UndefOpConversion, UnreachableOpConversion, XArrayCoorOpConversion,
-      XEmboxOpConversion, XReboxOpConversion, ZeroOpConversion>(converter,
-                                                                options);
+      LocalitySpecifierOpConversion, MulcOpConversion, NegcOpConversion,
+      NoReassocOpConversion, SelectCaseOpConversion, SelectOpConversion,
+      SelectRankOpConversion, SelectTypeOpConversion, ShapeOpConversion,
+      ShapeShiftOpConversion, ShiftOpConversion, SliceOpConversion,
+      StoreOpConversion, StringLitOpConversion, SubcOpConversion,
+      TypeDescOpConversion, TypeInfoOpConversion, UnboxCharOpConversion,
+      UnboxProcOpConversion, UndefOpConversion, UnreachableOpConversion,
+      XArrayCoorOpConversion, XEmboxOpConversion, XReboxOpConversion,
+      ZeroOpConversion>(converter, options);
 
   // Patterns that are populated without a type converter do not trigger
   // target materializations for the operands of the root op.

flang/test/Fir/local.fir

@@ -0,0 +1,10 @@
+// RUN: fir-opt --fir-to-llvm-ir %s | FileCheck %s
+
+// Tests that `fir.local` ops are dropped from the module before LLVM lowering.
+
+fir.local {type = local} @local_privatizer : i32
+func.func @foo() {
+  return
+}
+
+// CHECK-NOT: fir.local