[PATCH] D19845: [LTO] Add an option to enable fast-isel

[Rafael Espíndola via llvm-commits]

Is this something you expect to be generally useful or something that is
only needed to run some experiments.

Is there an equivalent option in the gold plugin or in lib lto?
On May 2, 2016 8:42 PM, "Davide Italiano" <dccitaliano at gmail.com> wrote:

> davide created this revision.
> davide added reviewers: pcc, rafael.
> davide added a subscriber: llvm-commits.
> Herald added a subscriber: joker.eph.
>
> http://reviews.llvm.org/D19845
>
> Files:
>   ELF/Config.h
>   ELF/Driver.cpp
>   ELF/LTO.cpp
>   ELF/Options.td
>   test/ELF/lto/fast-isel.ll
>
> Index: test/ELF/lto/fast-isel.ll
> ===================================================================
> --- /dev/null
> +++ test/ELF/lto/fast-isel.ll
> @@ -0,0 +1,38 @@
> +; Test the -lto-fast-isel option.
> +
> +; REQUIRES: x86
> +; RUN: rm -f %t.so.lto.bc %t.so.lto.opt.bc %t.so.lto.o
> +; RUN: llvm-as %s -o %t.o
> +; RUN: ld.lld -m elf_x86_64 %t.o -o %t.so -save-temps --lto-fast-isel
> -shared
> +; RUN: llvm-objdump -d %t.so | FileCheck %s
> +; RUN: ld.lld -m elf_x86_64 %t.o -o %t2.so -save-temps -shared
> +; RUN: llvm-objdump -d %t2.so | FileCheck %s --check-prefix=NOISEL
> +
> +target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
> +target triple = "x86_64-none-linux"
> +
> +define i32* @foo(i32* %p, i32* %q, i32** %z) {
> +entry:
> +  %r = load i32, i32* %p
> +  %s = load i32, i32* %q
> +  %y = load i32*, i32** %z
> +
> +  %t0 = add i32 %r, %s
> +  %t1 = add i32 %t0, 1
> +  %t2 = getelementptr i32, i32* %y, i32 1
> +  %t3 = getelementptr i32, i32* %t2, i32 %t1
> +
> +  ret i32* %t3
> +}
> +
> +; CHECK:      addl    $1, %eax
> +; CHECK-NEXT: addq    $4, %rcx
> +; CHECK-NEXT: cltq
> +; CHECK-NEXT: shlq    $2, %rax
> +; CHECK-NEXT: addq    %rcx, %rax
> +; CHECK-NEXT: retq
> +
> +; NOISEL:      leal    1(%rax,%rcx), %eax
> +; NOISEL-NEXT: cltq
> +; NOISEL-NEXT: leaq    4(%rdx,%rax,4), %rax
> +; NOISEL-NEXT: retq
> Index: ELF/Options.td
> ===================================================================
> --- ELF/Options.td
> +++ ELF/Options.td
> @@ -253,6 +253,7 @@
>  def alias_version_script_version_script : Joined<["--"],
> "version-script=">, Alias<version_script>;
>
>  // LTO-related options.
> +def lto_fast_isel : Flag<["--"], "lto-fast-isel">;
>  def lto_jobs : Joined<["--"], "lto-jobs=">,
>    HelpText<"Number of threads to run codegen">;
>  def disable_verify : Flag<["-"], "disable-verify">;
> Index: ELF/LTO.cpp
> ===================================================================
> --- ELF/LTO.cpp
> +++ ELF/LTO.cpp
> @@ -199,8 +199,10 @@
>    Reloc::Model R = Config->Pic ? Reloc::PIC_ : Reloc::Static;
>
>    auto CreateTargetMachine = [&]() {
> -    return std::unique_ptr<TargetMachine>(
> +    auto TM = std::unique_ptr<TargetMachine>(
>          T->createTargetMachine(TheTriple, "", "", Options, R));
> +    TM->setFastISel(Config->LtoFastIsel);
> +    return TM;
>    };
>
>    std::unique_ptr<TargetMachine> TM = CreateTargetMachine();
> Index: ELF/Driver.cpp
> ===================================================================
> --- ELF/Driver.cpp
> +++ ELF/Driver.cpp
> @@ -332,6 +332,7 @@
>    Config->ExportDynamic = Args.hasArg(OPT_export_dynamic);
>    Config->GcSections = Args.hasArg(OPT_gc_sections);
>    Config->ICF = Args.hasArg(OPT_icf);
> +  Config->LtoFastIsel = Args.hasArg(OPT_lto_fast_isel);
>    Config->NoGnuUnique = Args.hasArg(OPT_no_gnu_unique);
>    Config->NoUndefined = Args.hasArg(OPT_no_undefined);
>    Config->NoinhibitExec = Args.hasArg(OPT_noinhibit_exec);
> Index: ELF/Config.h
> ===================================================================
> --- ELF/Config.h
> +++ ELF/Config.h
> @@ -68,6 +68,7 @@
>    bool GcSections;
>    bool GnuHash = false;
>    bool ICF;
> +  bool LtoFastIsel;
>    bool Mips64EL = false;
>    bool NoGnuUnique;
>    bool NoUndefined;
>
>
>
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