[Metal] Add correct addrspace to global constants (#648)

Co-authored-by: Tim Besard <[email protected]>

Author: tgymnich

src/metal.jl

@@ -162,7 +162,8 @@ function finish_ir!(@nospecialize(job::CompilerJob{MetalCompilerTarget}), mod::L
 
     # add kernel metadata
     if job.config.kernel
-        entry = add_address_spaces!(job, mod, entry)
+        entry = add_parameter_address_spaces!(job, mod, entry)
+        entry = add_global_address_spaces!(job, mod, entry)
 
         add_argument_metadata!(job, mod, entry)
 
@@ -199,10 +200,12 @@ function finish_ir!(@nospecialize(job::CompilerJob{MetalCompilerTarget}), mod::L
     end
 
     # perform codegen passes that would normally run during machine code emission
-    # XXX: codegen passes don't seem available in the new pass manager yet
-    @dispose pm=ModulePassManager() begin
-        expand_reductions!(pm)
-        run!(pm, mod)
+    if LLVM.has_oldpm()
+        # XXX: codegen passes don't seem available in the new pass manager yet
+        @dispose pm=ModulePassManager() begin
+            expand_reductions!(pm)
+            run!(pm, mod)
+        end
     end
 
     return functions(mod)[entry_fn]
@@ -226,7 +229,8 @@ end
 # NOTE: this pass also only rewrites pointers _without_ address spaces, which requires it to
 # be executed after optimization (where Julia's address spaces are stripped). If we ever
 # want to execute it earlier, adapt remapType to rewrite all pointer types.
-function add_address_spaces!(@nospecialize(job::CompilerJob), mod::LLVM.Module, f::LLVM.Function)
+function add_parameter_address_spaces!(@nospecialize(job::CompilerJob), mod::LLVM.Module,
+                                       f::LLVM.Function)
     ft = function_type(f)
 
     # find the byref parameters
@@ -332,6 +336,92 @@ function add_address_spaces!(@nospecialize(job::CompilerJob), mod::LLVM.Module,
     return new_f
 end
 
+# update address spaces of constant global objects
+#
+# global constant objects need to reside in address space 2, so we clone each function
+# that uses global objects and rewrite the globals used by it
+function add_global_address_spaces!(@nospecialize(job::CompilerJob), mod::LLVM.Module,
+                                    entry::LLVM.Function)
+    # determine global variables we need to update
+    global_map = Dict{LLVM.Value, LLVM.Value}()
+    for gv in globals(mod)
+        isconstant(gv) || continue
+        addrspace(value_type(gv)) == 0 || continue
+
+        gv_ty = global_value_type(gv)
+        gv_name = LLVM.name(gv)
+
+        LLVM.name!(gv, gv_name * ".old")
+        new_gv = GlobalVariable(mod, gv_ty, gv_name, 2)
+
+        alignment!(new_gv, alignment(gv))
+        unnamed_addr!(new_gv, unnamed_addr(gv))
+        initializer!(new_gv, initializer(gv))
+        constant!(new_gv, true)
+        linkage!(new_gv, linkage(gv))
+        visibility!(new_gv, visibility(gv))
+
+        # we can't map the global variable directly, as the type change won't be applied
+        # recursively. so instead map a constant expression converting the value of the
+        # global into one with the old address space, avoiding a type change.
+        ptr = const_addrspacecast(new_gv, value_type(gv))
+
+        global_map[gv] = ptr
+    end
+    isempty(global_map) && return entry
+
+    # determine which functions we need to update
+    function_worklist = Set{LLVM.Function}()
+    function check_user(val)
+        if val isa LLVM.Instruction
+            bb = LLVM.parent(val)
+            f = LLVM.parent(bb)
+
+            push!(function_worklist, f)
+        elseif val isa LLVM.ConstantExpr
+            for use in uses(val)
+                check_user(user(use))
+            end
+        end
+    end
+    for gv in keys(global_map), use in uses(gv)
+        check_user(user(use))
+    end
+
+    # update functions that use the global
+    if !isempty(function_worklist)
+        entry_fn = LLVM.name(entry)
+        for fun in function_worklist
+            fn = LLVM.name(fun)
+
+            new_fun = clone(fun; value_map=global_map)
+            replace_uses!(fun, new_fun)
+            replace_metadata_uses!(fun, new_fun)
+            erase!(fun)
+
+            LLVM.name!(new_fun, fn)
+        end
+        entry = LLVM.functions(mod)[entry_fn]
+    end
+
+    # delete old globals
+    for (old, new) in global_map
+        for use in uses(old)
+            val = user(use)
+            if val isa ConstantExpr
+                # XXX: shouldn't clone_into! remove unused CEs?
+                isempty(uses(val)) || error("old function still has uses (via a constant expr)")
+                LLVM.unsafe_destroy!(val)
+            end
+        end
+        @assert isempty(uses(old))
+        replace_metadata_uses!(old, new)
+        erase!(old)
+    end
+
+    return entry
+end
+
 
 # value-to-reference conversion
 #

test/metal_tests.jl

@@ -89,7 +89,7 @@ end
         declare void @llvm.va_start(i8*)
         declare void @llvm.va_end(i8*)
         declare void @air.os_log(i8*, i64)
-        
+
         define void @metal_os_log(...) {
             %1 = alloca i8*
             %2 = bitcast i8** %1 to i8*
@@ -126,6 +126,22 @@ end
     end
 end
 
+@testset "constant globals" begin
+    mod = @eval module $(gensym())
+        const xs = (1.0f0, 2f0)
+
+        function kernel(ptr, i)
+            unsafe_store!(ptr, xs[i])
+
+            return
+        end
+    end
+
+    ir = sprint(io->Metal.code_llvm(io, mod.kernel, Tuple{Core.LLVMPtr{Float32,1}, Int};
+                                    dump_module=true, kernel=true))
+    @test occursin("addrspace(2) constant [2 x float]", ir)
+end
+
 end
 
 end