[llvm] r270246 - [X86] Reduce memory allocations in X86TargetMachine::getSubtargetImpl

[Benjamin Kramer via llvm-commits]

On Fri, May 20, 2016 at 8:17 PM, David Majnemer via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> Author: majnemer
> Date: Fri May 20 13:16:06 2016
> New Revision: 270246
>
> URL: http://llvm.org/viewvc/llvm-project?rev=270246&view=rev
> Log:
> [X86] Reduce memory allocations in X86TargetMachine::getSubtargetImpl
>
> We performed a number of memory allocations each time getTTI was called,
> remove them by using SmallString.
> No functionality change intended.
>
> Modified:
>     llvm/trunk/lib/Target/X86/X86Subtarget.cpp
>     llvm/trunk/lib/Target/X86/X86Subtarget.h
>     llvm/trunk/lib/Target/X86/X86TargetMachine.cpp
>
> Modified: llvm/trunk/lib/Target/X86/X86Subtarget.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86Subtarget.cpp?rev=270246&r1=270245&r2=270246&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/X86/X86Subtarget.cpp (original)
> +++ llvm/trunk/lib/Target/X86/X86Subtarget.cpp Fri May 20 13:16:06 2016
> @@ -353,8 +353,8 @@ X86Subtarget &X86Subtarget::initializeSu
>    return *this;
>  }
>
> -X86Subtarget::X86Subtarget(const Triple &TT, const std::string &CPU,
> -                           const std::string &FS, const X86TargetMachine &TM,
> +X86Subtarget::X86Subtarget(const Triple &TT, StringRef CPU, StringRef FS,
> +                           const X86TargetMachine &TM,
>                             unsigned StackAlignOverride)
>      : X86GenSubtargetInfo(TT, CPU, FS), X86ProcFamily(Others),
>        PICStyle(PICStyles::None), TM(TM), TargetTriple(TT),
>
> Modified: llvm/trunk/lib/Target/X86/X86Subtarget.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86Subtarget.h?rev=270246&r1=270245&r2=270246&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/X86/X86Subtarget.h (original)
> +++ llvm/trunk/lib/Target/X86/X86Subtarget.h Fri May 20 13:16:06 2016
> @@ -313,7 +313,7 @@ public:
>    /// This constructor initializes the data members to match that
>    /// of the specified triple.
>    ///
> -  X86Subtarget(const Triple &TT, const std::string &CPU, const std::string &FS,
> +  X86Subtarget(const Triple &TT, StringRef CPU, StringRef FS,
>                 const X86TargetMachine &TM, unsigned StackAlignOverride);
>
>    const X86TargetLowering *getTargetLowering() const override {
>
> Modified: llvm/trunk/lib/Target/X86/X86TargetMachine.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86TargetMachine.cpp?rev=270246&r1=270245&r2=270246&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/X86/X86TargetMachine.cpp (original)
> +++ llvm/trunk/lib/Target/X86/X86TargetMachine.cpp Fri May 20 13:16:06 2016
> @@ -182,12 +182,12 @@ X86TargetMachine::getSubtargetImpl(const
>    Attribute CPUAttr = F.getFnAttribute("target-cpu");
>    Attribute FSAttr = F.getFnAttribute("target-features");
>
> -  std::string CPU = !CPUAttr.hasAttribute(Attribute::None)
> -                        ? CPUAttr.getValueAsString().str()
> -                        : TargetCPU;
> -  std::string FS = !FSAttr.hasAttribute(Attribute::None)
> -                       ? FSAttr.getValueAsString().str()
> -                       : TargetFS;
> +  SmallString<32> CPU = !CPUAttr.hasAttribute(Attribute::None)
> +                            ? CPUAttr.getValueAsString()
> +                            : (StringRef)TargetCPU;

This could be a StringRef, conserves precious stack space and avoids a copy.

> +  SmallString<512> FS = !FSAttr.hasAttribute(Attribute::None)
> +                            ? FSAttr.getValueAsString()
> +                            : (StringRef)TargetFS;

same, but then append directly to Key instead of FS below for the
softfloat stuff.

>
>    // FIXME: This is related to the code below to reset the target options,
>    // we need to know whether or not the soft float flag is set on the
> @@ -201,7 +201,12 @@ X86TargetMachine::getSubtargetImpl(const
>    if (SoftFloat)
>      FS += FS.empty() ? "+soft-float" : ",+soft-float";
>
> -  auto &I = SubtargetMap[CPU + FS];
> +  SmallString<544> Key;

512+32 = not a round number :(

> +  Key.reserve(CPU.size() + FS.size());
> +  Key += CPU;
> +  Key += FS;
> +
> +  auto &I = SubtargetMap[Key];
>    if (!I) {
>      // This needs to be done before we create a new subtarget since any
>      // creation will depend on the TM and the code generation flags on the
>
>
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