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

[Quentin Colombet via llvm-commits]

Hi Davide,

Shouldn’t fast isel be an attribute inherited from each individual compiler invocation to produce the bitcode files?
I.e., shouldn’t it be a function attribute?

Note: I am not very familiar of how LTO is supposed to work so you can just ignore my remarks :).

Cheers,
-Quentin
> On May 2, 2016, at 5:42 PM, Davide Italiano via llvm-commits <llvm-commits at lists.llvm.org> 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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