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Merge pull request #4320 from kinke/dead_strip
Be less conservative wrt. linker dead code elimination
This commit is contained in:
Martin Kinkelin
GitHub
commit
aa9b2783bb
6 changed files with 66 additions and 50 deletions
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@ -1,6 +1,7 @@
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# LDC master
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#### Big news
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- Linker-level dead code elimination is enabled by default for Apple, wasm and *all* ELF targets too now. (#4320)
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#### Platform support
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@ -635,33 +635,6 @@ if(LDC_WITH_LLD)
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endif()
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endif()
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# Plugin support
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if(UNIX)
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set(LDC_ENABLE_PLUGINS_DEFAULT ON)
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else()
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set(LDC_ENABLE_PLUGINS_DEFAULT OFF)
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endif()
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set(LDC_ENABLE_PLUGINS ${LDC_ENABLE_PLUGINS_DEFAULT} CACHE BOOL "Build LDC with plugin support (increases binary size)")
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if(LDC_ENABLE_PLUGINS)
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add_definitions(-DLDC_ENABLE_PLUGINS)
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if(APPLE)
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# No extra link flags needed.
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elseif(UNIX)
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# For plugin support, we need to link with --export-dynamic on Unix.
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# Make sure the linker supports --export-dynamic (on Solaris it is not supported and also not needed).
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set(CMAKE_REQUIRED_QUIET_BAK ${CMAKE_REQUIRED_QUIET})
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set(CMAKE_REQUIRED_QUIET ON) # suppress status messages
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CHECK_LINK_FLAG("--export-dynamic" LINKER_ACCEPTS_EXPORT_DYNAMIC_FLAG)
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set(CMAKE_REQUIRED_QUIET ${CMAKE_REQUIRED_QUIET_BAK})
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if(LINKER_ACCEPTS_EXPORT_DYNAMIC_FLAG)
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set(LDC_LINKERFLAG_LIST "${LDC_LINKERFLAG_LIST};-Wl,--export-dynamic")
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endif()
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endif()
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endif()
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message(STATUS "-- Building LDC with plugin support (LDC_ENABLE_PLUGINS): ${LDC_ENABLE_PLUGINS}")
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if(NOT DEFINED LDC_LINK_MANUALLY)
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if(MSVC)
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# Use the D host compiler for linking D executables.
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@ -678,6 +651,42 @@ if(LDC_LINK_MANUALLY AND NOT DEFINED D_LINKER_ARGS)
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message(STATUS "Host D compiler linker flags: ${D_LINKER_ARGS}")
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endif()
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# Plugin support
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if(UNIX)
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set(LDC_ENABLE_PLUGINS_DEFAULT ON)
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else()
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set(LDC_ENABLE_PLUGINS_DEFAULT OFF)
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endif()
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set(LDC_ENABLE_PLUGINS ${LDC_ENABLE_PLUGINS_DEFAULT} CACHE BOOL "Build LDC with plugin support (increases binary size)")
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if(LDC_ENABLE_PLUGINS)
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add_definitions(-DLDC_ENABLE_PLUGINS)
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if(APPLE)
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# Need to disable dead_strip with LDC host compilers.
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if("${D_COMPILER_ID}" STREQUAL "LDMD")
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if(LDC_LINK_MANUALLY)
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# suboptimal - applies to all D executables (incl. ldmd2, ldc-build-runtime, ldc-prune-cache)
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list(REMOVE_ITEM D_LINKER_ARGS "-Wl,-dead_strip")
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else()
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# just for ldc2 (and ldc2-unittest)
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append("-disable-linker-strip-dead" DFLAGS_LDC)
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endif()
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endif()
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elseif(UNIX)
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# For plugin support, we need to link with --export-dynamic on Unix.
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# Make sure the linker supports --export-dynamic (on Solaris it is not supported and also not needed).
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set(CMAKE_REQUIRED_QUIET_BAK ${CMAKE_REQUIRED_QUIET})
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set(CMAKE_REQUIRED_QUIET ON) # suppress status messages
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CHECK_LINK_FLAG("--export-dynamic" LINKER_ACCEPTS_EXPORT_DYNAMIC_FLAG)
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set(CMAKE_REQUIRED_QUIET ${CMAKE_REQUIRED_QUIET_BAK})
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if(LINKER_ACCEPTS_EXPORT_DYNAMIC_FLAG)
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set(LDC_LINKERFLAG_LIST "${LDC_LINKERFLAG_LIST};-Wl,--export-dynamic")
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endif()
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endif()
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endif()
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message(STATUS "-- Building LDC with plugin support (LDC_ENABLE_PLUGINS): ${LDC_ENABLE_PLUGINS}")
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build_d_executable(
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"${LDC_EXE}"
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"${LDC_EXE_FULL}"
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@ -479,6 +479,8 @@ void ArgsBuilder::addSanitizers(const llvm::Triple &triple) {
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void ArgsBuilder::build(llvm::StringRef outputPath,
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const std::vector<std::string> &defaultLibNames) {
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const auto &triple = *global.params.targetTriple;
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// object files
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for (auto objfile : global.params.objfiles) {
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args.push_back(objfile);
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@ -494,7 +496,7 @@ void ArgsBuilder::build(llvm::StringRef outputPath,
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// Link with profile-rt library when generating an instrumented binary.
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if (opts::isInstrumentingForPGO()) {
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addProfileRuntimeLinkFlags(*global.params.targetTriple);
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addProfileRuntimeLinkFlags(triple);
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}
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if (opts::enableDynamicCompile) {
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@ -521,10 +523,10 @@ void ArgsBuilder::build(llvm::StringRef outputPath,
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args.push_back("-o");
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args.push_back(std::string(outputPath));
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addSanitizers(*global.params.targetTriple);
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addSanitizers(triple);
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if (opts::fXRayInstrument) {
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addXRayLinkFlags(*global.params.targetTriple);
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addXRayLinkFlags(triple);
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}
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// Add LTO link flags before adding the user link switches, such that the user
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@ -559,16 +561,14 @@ void ArgsBuilder::build(llvm::StringRef outputPath,
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addLdFlag("-rpath", rpath);
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}
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if (global.params.targetTriple->getOS() == llvm::Triple::Linux ||
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(global.params.targetTriple->getOS() == llvm::Triple::FreeBSD &&
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(useInternalLLDForLinking() ||
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(!opts::linker.empty() && opts::linker != "bfd") ||
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(opts::linker.empty() && isLldDefaultLinker())))) {
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// Make sure we don't do --gc-sections when generating a profile-
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// instrumented binary. The runtime relies on magic sections, which
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// would be stripped by gc-section on older version of ld, see bug:
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// https://sourceware.org/bugzilla/show_bug.cgi?id=19161
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if (!opts::disableLinkerStripDead && !opts::isInstrumentingForPGO()) {
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// Make sure we don't do --gc-sections when generating a profile-
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// instrumented binary. The runtime relies on magic sections, which
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// would be stripped by gc-section on older version of ld, see bug:
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// https://sourceware.org/bugzilla/show_bug.cgi?id=19161
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if (!opts::disableLinkerStripDead && !opts::isInstrumentingForPGO()) {
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if (triple.isOSBinFormatMachO()) {
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addLdFlag("-dead_strip");
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} else {
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addLdFlag("--gc-sections");
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}
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}
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@ -505,14 +505,14 @@ createTargetMachine(const std::string targetTriple, const std::string arch,
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break;
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}
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// Right now, we only support linker-level dead code elimination on Linux
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// and FreeBSD using GNU or LLD linkers (based on the --gc-sections flag).
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// The Apple ld on OS X supports a similar flag (-dead_strip) that doesn't
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// require emitting the symbols into different sections. The MinGW ld doesn't
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// seem to support --gc-sections at all.
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if (!noLinkerStripDead && (triple.getOS() == llvm::Triple::Linux ||
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triple.getOS() == llvm::Triple::FreeBSD ||
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triple.getOS() == llvm::Triple::Win32)) {
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// Linker-level dead code elimination for ELF/wasm binaries using GNU or LLD
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// linkers (based on the --gc-sections flag) requires a separate section per
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// symbol.
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// The Apple ld64 on macOS supports a similar flag (-dead_strip) that doesn't
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// require emitting the symbols into different sections.
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// On Windows, the MSVC link.exe / lld-link.exe has `/REF`; LLD enforces
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// separate sections with LTO, so do the same here.
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if (!noLinkerStripDead && !triple.isOSBinFormatMachO()) {
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targetOptions.FunctionSections = true;
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targetOptions.DataSections = true;
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}
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@ -150,7 +150,12 @@ void IrGlobal::define() {
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// If this global is used from a naked function, we need to create an
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// artificial "use" for it, or it could be removed by the optimizer if
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// the only reference to it is in inline asm.
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if (nakedUse) {
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// Also prevent linker-level dead-symbol-elimination from stripping
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// special `rt_*` druntime symbol overrides (e.g., from executables linked
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// against *shared* druntime; required at least for Apple's ld64 linker).
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const auto name = gvar->getName();
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if (nakedUse || name == "rt_options" || name == "rt_envvars_enabled" ||
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name == "rt_cmdline_enabled") {
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gIR->usedArray.push_back(gvar);
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}
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@ -10,7 +10,8 @@ GREP:=grep
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.PHONY: all clean
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all: $(addprefix $(ROOT)/,$(addsuffix .done,$(TESTS)))
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$(ROOT)/profile.done: DFLAGS+=-profile
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# LDC: enable assertions for BUILD=RELEASE (=> `-O -release`)
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$(ROOT)/profile.done: DFLAGS+=-profile -check=assert=on
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$(ROOT)/profile.done: $(ROOT)/%.done: $(ROOT)/%
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@echo Testing $*
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@rm -f $(ROOT)/mytrace.log $(ROOT)/mytrace.def
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