Save a reference to the function name instead.

Works around an LLVM limitation.

Author: maleadt

src/driver.jl

@@ -321,7 +321,11 @@ const __llvm_initialized = Ref(false)
         if deferred_codegen
             # IDEA: save other parts of the CompileJob (so that we can reconstruct it
             #       instead of setting it globally, which is incompatible with threading)?
-            push!(metadata(ir)["julia.entry"], MDNode([entry]; ctx))
+            # XXX: we want to save the actual function here, but due to our passes rewriting
+            #      functions, and the inability to RAUW values with a different type, that
+            #      metadata gets lost. So instead we save the function name. See also:
+            #      https://discourse.llvm.org/t/replacing-module-metadata-uses-of-function/62431
+            push!(metadata(ir)["julia.entry"], MDNode([MDString(LLVM.name(entry); ctx)]; ctx))
         end
 
         if optimize

src/irgen.jl

@@ -552,9 +552,8 @@ function add_kernel_state!(mod::LLVM.Module)
     state_intr = kernel_state_intr(mod, T_state)
 
     entry_md = operands(metadata(mod)["julia.entry"])[1]
-    entry = Value(operands(entry_md)[1]; ctx)
-    # XXX: this metadata will be invalid after the replacement here (it'll be null).
-    #      how do we replace Metadata uses? Normally RAUW, but it asserts type equality
+    entry_fn = string(operands(entry_md)[1])
+    entry = functions(mod)[entry_fn]
 
     # determine which functions need a kernel state argument
     #

src/ptx.jl

@@ -199,8 +199,8 @@ function finish_ir!(@nospecialize(job::CompilerJob{PTXCompilerTarget}),
         # add metadata annotations for the assembler to the module
 
         # NOTE: we do this here, rather than in finish_module!, because otherwise
-        #       the metadata is lost when functions are cloned.
-        # XXX: why does this happen? shouldn't cloning preserve metadata?
+        #       the metadata is lost when functions are cloned. See also:
+        #       https://discourse.llvm.org/t/replacing-module-metadata-uses-of-function/62431
 
         # property annotations
         annotations = Metadata[entry]