Cover the function definition line of device code. (#866)

The :code_coverage_effect expressions only mark body statements; Julia's
codegen visits the signature line separately at the function prologue. Mirror
that, or the header shows as missed while the body is hit.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: maleadt

src/jlgen.jl

@@ -715,9 +715,20 @@ end
 # Julia runtime, so instead we mark those lines as visited when compiling them: Coverage of
 # device code thus means "this code was compiled", with counts reflecting the number of
 # compilations rather than executions.
-function record_coverage(src::CodeInfo)
+function coverage_visit_line(@nospecialize(file), line::Integer)
+    file isa Symbol || return
+    filename = String(file)
+    (isempty(filename) || line <= 0) && return
+    ccall(:jl_coverage_visit_line, Cvoid, (Cstring, Csize_t, Cint),
+          filename, ncodeunits(filename), line)
+    return
+end
+
+function record_coverage(mi::MethodInstance, src::CodeInfo)
+    tracked = false
     for (pc, stmt) in enumerate(src.code)
         (stmt isa Expr && stmt.head === :code_coverage_effect) || continue
+        tracked = true
         @static if VERSION >= v"1.12-"
             scopes = Base.IRShow.buildLineInfoNode(src.debuginfo, nothing, pc)
             isempty(scopes) && continue
@@ -729,11 +740,17 @@ function record_coverage(src::CodeInfo)
             loc = src.linetable[lineidx]::Core.LineInfoNode
             file, line = loc.file, loc.line
         end
-        file isa Symbol || continue
-        filename = String(file)
-        (isempty(filename) || line <= 0) && continue
-        ccall(:jl_coverage_visit_line, Cvoid, (Cstring, Csize_t, Cint),
-              filename, ncodeunits(filename), line)
+        coverage_visit_line(file, line)
+    end
+
+    # the definition (signature) line isn't a `:code_coverage_effect`; Julia's codegen
+    # visits it separately at the prologue. Mirror that, gated on the body being tracked,
+    # or the signature reads as missed while the body is hit.
+    if tracked
+        def = mi.def
+        if def isa Method
+            coverage_visit_line(def.file, def.line)
+        end
     end
     return
 end
@@ -760,7 +777,7 @@ function compile_method_instance(@nospecialize(job::CompilerJob))
     # `ci_cache_populate` does not return sources, this happens after codegen instead)
     if Base.JLOptions().code_coverage != 0
         for (ci, src) in populated
-            record_coverage(src)
+            record_coverage(ci.def::MethodInstance, src)
         end
     end
 
@@ -1017,7 +1034,7 @@ function compile_method_instance(@nospecialize(job::CompilerJob))
                 src = Base._uncompressed_ir(ci, src)
             end
             if src isa CodeInfo
-                record_coverage(src)
+                record_coverage(ci.def::MethodInstance, src)
             end
         end
     end

test/native.jl

@@ -229,6 +229,14 @@ end
             @inline inlined_callee(x) = x + one(x)
             @noinline noinline_callee(x) = x * 2
             entry(x) = noinline_callee(inlined_callee(x))
+
+            # a genuinely multi-line function, so its definition (signature) line is
+            # distinct from its body lines; compiled as its own entry below.
+            function multiline(x)
+                y = x + 1
+                z = y * 2
+                return z
+            end
         end
 
         # whether any line in `lo:hi` of `file` has a nonzero execution count in an
@@ -248,24 +256,49 @@ end
             return false
         end
 
+        # the execution count recorded for an exact line of `file`, or `nothing` if that
+        # line was not instrumented
+        function lcov_line_count(tracefile, file, line)
+            in_block = false
+            for l in eachline(tracefile)
+                if startswith(l, "SF:")
+                    in_block = (l == "SF:" * file)
+                elseif l == "end_of_record"
+                    in_block = false
+                elseif in_block && startswith(l, "DA:")
+                    ln, cnt = parse.(Int, split(l[4:end], ","))
+                    ln == line && return cnt
+                end
+            end
+            return nothing
+        end
+
         if Base.JLOptions().code_coverage == 0
             @test_skip "requires --code-coverage"
         else
-            job, _ = Native.create_job(mod.entry, (Int,))
-            JuliaContext() do ctx
-                GPUCompiler.compile(:asm, job)
+            for entry in (mod.entry, mod.multiline)
+                job, _ = Native.create_job(entry, (Int,))
+                JuliaContext() do ctx
+                    GPUCompiler.compile(:asm, job)
+                end
             end
 
-            # flush coverage data in-process; the device functions must show covered
-            # lines even though they were never executed by the host.
-            mktempdir() do dir
-                tracefile = joinpath(dir, "coverage.info")
-                ccall(:jl_write_coverage_data, Cvoid, (Cstring,), tracefile)
-                for f in (mod.inlined_callee, mod.noinline_callee, mod.entry)
-                    m = only(methods(f))
-                    @test lcov_any_covered(tracefile, string(m.file), m.line, m.line + 1)
-                end
+            # flush coverage in-process; device lines show covered despite never running.
+            # bare mktempdir (cleaned at exit, after a GC) dodges the EBUSY `rm` race the
+            # `do` form hits on Windows. jl_write_coverage_data needs a `.info` path.
+            dir = mktempdir()
+            tracefile = joinpath(dir, "coverage.info")
+            ccall(:jl_write_coverage_data, Cvoid, (Cstring,), tracefile)
+            for f in (mod.inlined_callee, mod.noinline_callee, mod.entry)
+                m = only(methods(f))
+                @test lcov_any_covered(tracefile, string(m.file), m.line, m.line + 1)
             end
+
+            # the definition line must be covered too, not just the body (Julia covers
+            # it separately at the prologue)
+            m = only(methods(mod.multiline))
+            @test lcov_line_count(tracefile, string(m.file), m.line) !== nothing
+            @test something(lcov_line_count(tracefile, string(m.file), m.line), 0) >= 1
         end
     end
 end