[DTLTO][Clang] Add support for Integrated Distributed ThinLTO

clang/docs/ThinLTO.rst

@@ -240,6 +240,38 @@ The ``BOOTSTRAP_LLVM_ENABLE_LTO=Thin`` will enable ThinLTO for stage 2 and
 stage 3 in case the compiler used for stage 1 does not support the ThinLTO
 option.
 
+Integrated Distributed ThinLTO (DTLTO)
+--------------------------------------
+
+Integrated Distributed ThinLTO (DTLTO) enables the distribution of backend
+ThinLTO compilations via external distribution systems, such as Incredibuild,
+during the traditional link step.
+
+The implementation is documented here: https://llvm.org/docs/DTLTO.html.
+
+DTLTO requires the LLD linker (``-fuse-ld=lld``).
+
+``-fthinlto-distributor=<path>``
+   - Specifies the ``<path>`` to the distributor process executable for DTLTO.
+   - If specified, ThinLTO backend compilations will be distributed by LLD.
+
+``-Xthinlto-distributor=<arg>``
+   - Passes ``<arg>`` to the distributor process (see ``-fthinlto-distributor=``).
+   - Can be specified multiple times to pass multiple options.
+   - Multiple options can also be specified by separating them with commas.
+
+Examples:
+   - ``clang -flto=thin -fthinlto-distributor=incredibuild.exe -Xthinlto-distributor=--verbose,--j10 -fuse-ld=lld``
+   - ``clang -flto=thin -fthinlto-distributor=$(which python) -Xthinlto-distributor=incredibuild.py -fuse-ld=lld``
+
+If ``-fthinlto-distributor=`` is specified, Clang supplies the path to a
+compiler to be executed remotely to perform the ThinLTO backend
+compilations. Currently, this is Clang itself.
+
+Note that currently, DTLTO is only supported in some LLD flavors. Support can
+be added to other LLD flavours in the future.
+See `DTLTO <https://lld.llvm.org/dtlto.html>`_ for more information.
+
 More Information
 ================
 

clang/include/clang/Driver/Options.td

@@ -990,6 +990,13 @@ def Xlinker : Separate<["-"], "Xlinker">, Flags<[LinkerInput, RenderAsInput]>,
   Visibility<[ClangOption, CLOption, FlangOption]>,
   HelpText<"Pass <arg> to the linker">, MetaVarName<"<arg>">,
   Group<Link_Group>;
+def Xthinlto_distributor_EQ : CommaJoined<["-"], "Xthinlto-distributor=">,
+  Flags<[LinkOption]>,
+  Visibility<[ClangOption, CLOption]>,
+  HelpText<"Pass <arg> to the ThinLTO distributor process. Can be specified "
+           "multiple times or with comma-separated values.">,
+  MetaVarName<"<arg>">,
+  Group<Link_Group>;
 def Xoffload_linker : JoinedAndSeparate<["-"], "Xoffload-linker">,
   Visibility<[ClangOption, FlangOption]>,
   HelpText<"Pass <arg> to the offload linkers or the ones identified by -<triple>">,
@@ -4233,7 +4240,12 @@ def ffinite_loops: Flag<["-"],  "ffinite-loops">, Group<f_Group>,
 def fno_finite_loops: Flag<["-"], "fno-finite-loops">, Group<f_Group>,
   HelpText<"Do not assume that any loop is finite.">,
   Visibility<[ClangOption, CC1Option]>;
-
+def fthinlto_distributor_EQ : Joined<["-"], "fthinlto-distributor=">,
+  Group<f_Group>,
+  HelpText<"Path to the ThinLTO distributor process. If specified, "
+           "ThinLTO backend compilations will be distributed by LLD">,
+  MetaVarName<"<path>">,
+  Visibility<[ClangOption, CLOption]>;
 def ftrigraphs : Flag<["-"], "ftrigraphs">, Group<f_Group>,
   HelpText<"Process trigraph sequences">, Visibility<[ClangOption, CC1Option]>;
 def fno_trigraphs : Flag<["-"], "fno-trigraphs">, Group<f_Group>,

clang/lib/Driver/ToolChains/CommonArgs.cpp

@@ -1309,6 +1309,17 @@ void tools::addLTOOptions(const ToolChain &ToolChain, const ArgList &Args,
   if (Args.hasArg(options::OPT_ftime_report))
     CmdArgs.push_back(
         Args.MakeArgString(Twine(PluginOptPrefix) + "-time-passes"));
+
+  if (Arg *A = Args.getLastArg(options::OPT_fthinlto_distributor_EQ)) {
+    CmdArgs.push_back(
+        Args.MakeArgString("--thinlto-distributor=" + Twine(A->getValue())));
+    CmdArgs.push_back(
+        Args.MakeArgString("--thinlto-remote-compiler=" +
+                           Twine(ToolChain.getDriver().getClangProgramPath())));
+
+    for (auto A : Args.getAllArgValues(options::OPT_Xthinlto_distributor_EQ))
+      CmdArgs.push_back(Args.MakeArgString("--thinlto-distributor-arg=" + A));
+  }
 }
 
 void tools::addOpenMPRuntimeLibraryPath(const ToolChain &TC,

clang/test/Driver/DTLTO/dtlto.c

@@ -0,0 +1,48 @@
+// REQUIRES: lld
+
+/// Check DTLTO options are forwarded to the linker.
+
+/// Check that options are forwarded as expected with --thinlto-distributor=.
+// RUN: %clang -flto=thin %s -### -fuse-ld=lld --target=x86_64-linux-gnu \
+// RUN:   -Xthinlto-distributor=a1 -Xthinlto-distributor=a2,a3 \
+// RUN:   -fthinlto-distributor=d.exe -Werror 2>&1 | \
+// RUN:   FileCheck %s --check-prefix=FORWARD
+
+// FORWARD: ld.lld
+// FORWARD-SAME: "--thinlto-distributor=d.exe"
+// FORWARD-SAME: "--thinlto-remote-compiler={{.*}}clang{{[^\"]*}}"
+// FORWARD-SAME: "--thinlto-distributor-arg=a1"
+// FORWARD-SAME: "--thinlto-distributor-arg=a2"
+// FORWARD-SAME: "--thinlto-distributor-arg=a3"
+
+/// Check that options are not added without --thinlto-distributor= and
+/// that a warning is issued for unused -Xthinlto-distributor options.
+// RUN: %clang -flto=thin %s -### -fuse-ld=lld --target=x86_64-linux-gnu \
+// RUN:   -Xthinlto-distributor=a1 -Xthinlto-distributor=a2,a3 2>&1 | \
+// RUN:   FileCheck %s --check-prefix=NODIST --implicit-check-not=distributor \
+// RUN:     --implicit-check-not=remote-compiler
+
+// NODIST: warning: argument unused during compilation: '-Xthinlto-distributor=a1'
+// NODIST: warning: argument unused during compilation: '-Xthinlto-distributor=a2,a3'
+// NODIST: ld.lld
+
+/// Check the expected arguments are forwarded by default with only
+/// --thinlto-distributor=.
+// RUN: %clang -flto=thin %s -### -fuse-ld=lld --target=x86_64-linux-gnu \
+// RUN:   -fthinlto-distributor=d.exe -Werror 2>&1 | \
+// RUN:   FileCheck %s --check-prefix=DEFAULT --implicit-check-not=distributor \
+// RUN:     --implicit-check-not=remote-compiler
+
+// DEFAULT: ld.lld
+// DEFAULT-SAME: "--thinlto-distributor=d.exe"
+// DEFAULT-SAME: "--thinlto-remote-compiler={{.*}}clang{{[^\"]*}}"
+
+/// Check that nothing is forwarded when the compiler is not in LTO mode, and that
+/// appropriate unused option warnings are issued.
+// RUN: %clang %s -### -fuse-ld=lld --target=x86_64-linux-gnu \
+// RUN:   -fthinlto-distributor=d.exe 2>&1 | \
+// RUN:   FileCheck %s --check-prefix=NOFLTO --implicit-check-not=distributor \
+// RUN:     --implicit-check-not=remote-compiler
+
+// NOFLTO: warning: argument unused during compilation: '-fthinlto-distributor=d.exe'
+// NOFLTO: ld.lld

cross-project-tests/dtlto/ld-dtlto.c

@@ -5,13 +5,11 @@
 
 // RUN: rm -rf %t && mkdir %t && cd %t
 
-// RUN: %clang --target=x86_64-linux-gnu -c -flto=thin %s -o dtlto.o
-
-// RUN: ld.lld dtlto.o \
-// RUN:   --thinlto-distributor=%python \
-// RUN:   --thinlto-distributor-arg=%llvm_src_root/utils/dtlto/local.py \
-// RUN:   --thinlto-remote-compiler=%clang \
-// RUN:   --thinlto-remote-compiler-arg=--save-temps
+// RUN: %clang --target=x86_64-linux-gnu %s -flto=thin -fuse-ld=lld \
+// RUN:   -fthinlto-distributor=%python \
+// RUN:   -Xthinlto-distributor=%llvm_src_root/utils/dtlto/local.py \
+// RUN:   -Wl,--thinlto-remote-compiler-arg=--save-temps \
+// RUN:   -nostdlib -Werror
 
 /// Check that the required output files have been created.
 // RUN: ls | sort | FileCheck %s
@@ -22,18 +20,15 @@
 /// Linked ELF.
 // CHECK: {{^}}a.out{{$}}
 
-/// Produced by the bitcode compilation.
-// CHECK-NEXT: {{^}}dtlto.o{{$}}
-
 /// --save-temps output for the backend compilation.
-// CHECK-NEXT: {{^}}dtlto.s{{$}}
-// CHECK-NEXT: {{^}}dtlto.s.0.preopt.bc{{$}}
-// CHECK-NEXT: {{^}}dtlto.s.1.promote.bc{{$}}
-// CHECK-NEXT: {{^}}dtlto.s.2.internalize.bc{{$}}
-// CHECK-NEXT: {{^}}dtlto.s.3.import.bc{{$}}
-// CHECK-NEXT: {{^}}dtlto.s.4.opt.bc{{$}}
-// CHECK-NEXT: {{^}}dtlto.s.5.precodegen.bc{{$}}
-// CHECK-NEXT: {{^}}dtlto.s.resolution.txt{{$}}
+// CHECK-NEXT: {{^}}ld-dtlto-[[TMP:[a-zA-Z0-9_]+]].s{{$}}
+// CHECK-NEXT: {{^}}ld-dtlto-[[TMP]].s.0.preopt.bc{{$}}
+// CHECK-NEXT: {{^}}ld-dtlto-[[TMP]].s.1.promote.bc{{$}}
+// CHECK-NEXT: {{^}}ld-dtlto-[[TMP]].s.2.internalize.bc{{$}}
+// CHECK-NEXT: {{^}}ld-dtlto-[[TMP]].s.3.import.bc{{$}}
+// CHECK-NEXT: {{^}}ld-dtlto-[[TMP]].s.4.opt.bc{{$}}
+// CHECK-NEXT: {{^}}ld-dtlto-[[TMP]].s.5.precodegen.bc{{$}}
+// CHECK-NEXT: {{^}}ld-dtlto-[[TMP]].s.resolution.txt{{$}}
 
 /// No files are expected after.
 // CHECK-NOT: {{.}}