r193740 - [AArch64] Add some CPU targets for "generic", A-53 and A-57.
Eric Christopher
echristo at gmail.com
Thu Nov 7 14:09:18 PST 2013
On Thu, Nov 7, 2013 at 6:47 AM, Amara Emerson <amara.emerson at arm.com> wrote:
> Hi Eric,
>
>
>
> Some of the main reasons (there may be more I’m overlooking) for using
> this scheme is consistency with the existing ARM backend for end users.
> From our perspective, -march should be restricted to actual architectures,
> and not one specific implementation. A pragmatic addition is that accepting
> –march=cortex-a53 would be ambiguous, as cortex-a53 will exist in both the
> ARM and AArch64 backends. Specifying the CPU name alone is not enough to
> determine the architecture we’re compiling for. We’ve also never used
> –mtune, and to begin doing so would not bring us any significant benefits.
> Hope that answers your questions.
>
>
>
It seems odd to saddle the ARM64 port with the mistakes of the previous ARM
port. That there's going to be a cortex-a53 for arm64 and arm seems
irrelevant since, for the general -arch or -target case, you'll be
specifying the triple that you're compiling for so whether you're compiling
for 64 or 32-bit will be clear on the command line. Unless you have a plan
for cpu families ala the old ARM I really don't see a reason to have this
and a lot of reasons not to.
As far as -mtune, the ARM port was actually the only port in gcc that
didn't use -mtune and it caused a lot of odd bugs and complaints. I don't
see a reason to limit tuning for a particular processor while targeting the
architecture of something else.
Nigel: Can you elaborate here a bit more with the uses you see here?
-eric
> Amara
>
>
>
> *From:* Eric Christopher [mailto:echristo at gmail.com]
> *Sent:* 06 November 2013 16:34
> *To:* Amara Emerson
> *Cc:* cfe-commits at cs.uiuc.edu
> *Subject:* Re: r193740 - [AArch64] Add some CPU targets for "generic",
> A-53 and A-57.
>
>
>
> Ping? Can you answer this?
>
> On Nov 1, 2013 3:04 PM, "Eric Christopher" <echristo at gmail.com> wrote:
>
> Out of curiosity this seems to be enshrining for AArch64 the -march/-mcpu
> stuff from the old 32-bit arm gcc port. Why is this necessary? Why not just
> -march=cortex-a53 to generate code for a particular architecture and
> -mtune=cortex-a53 to tune, but not use any cpu specific instructions for a
> particular architecture? Can you explain what your thoughts are here?
>
>
>
> -eric
>
>
>
> On Thu, Oct 31, 2013 at 2:32 AM, Amara Emerson <amara.emerson at arm.com>
> wrote:
>
> Author: aemerson
> Date: Thu Oct 31 04:32:33 2013
> New Revision: 193740
>
> URL: http://llvm.org/viewvc/llvm-project?rev=193740&view=rev
> Log:
> [AArch64] Add some CPU targets for "generic", A-53 and A-57.
>
> Enables the clang driver to begin targeting specific CPUs. Introduced a
> "generic" CPU which will ensure that the optional FP feature is enabled
> by default when it gets to LLVM, without needing any extra arguments.
> Cortex-A53 and A-57 are also introduced with tests, although backend
> handling of them does not yet exist.
>
> Added:
> cfe/trunk/test/Driver/aarch64-cpus.c
> cfe/trunk/test/Driver/aarch64-mfpu.c
> Modified:
> cfe/trunk/lib/Basic/Targets.cpp
> cfe/trunk/lib/Driver/Tools.cpp
> cfe/trunk/lib/Driver/Tools.h
>
> Modified: cfe/trunk/lib/Basic/Targets.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Basic/Targets.cpp?rev=193740&r1=193739&r2=193740&view=diff
>
> ==============================================================================
> --- cfe/trunk/lib/Basic/Targets.cpp (original)
> +++ cfe/trunk/lib/Basic/Targets.cpp Thu Oct 31 04:32:33 2013
> @@ -3472,6 +3472,13 @@ public:
> return Feature == "aarch64" || (Feature == "neon" && FPU == NeonMode);
> }
>
> + virtual bool setCPU(const std::string &Name) {
> + return llvm::StringSwitch<bool>(Name)
> + .Case("generic", true)
> + .Cases("cortex-a53", "cortex-a57", true)
> + .Default(false);
> + }
> +
> virtual bool handleTargetFeatures(std::vector<std::string> &Features,
> DiagnosticsEngine &Diags) {
> FPU = FPUMode;
>
> Modified: cfe/trunk/lib/Driver/Tools.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Driver/Tools.cpp?rev=193740&r1=193739&r2=193740&view=diff
>
> ==============================================================================
> --- cfe/trunk/lib/Driver/Tools.cpp (original)
> +++ cfe/trunk/lib/Driver/Tools.cpp Thu Oct 31 04:32:33 2013
> @@ -539,6 +539,26 @@ static std::string getARMTargetCPU(const
> .Default("arm7tdmi");
> }
>
> +/// getAArch64TargetCPU - Get the (LLVM) name of the AArch64 cpu we are
> targeting.
> +//
> +// FIXME: tblgen this.
> +static std::string getAArch64TargetCPU(const ArgList &Args,
> + const llvm::Triple &Triple) {
> + // FIXME: Warn on inconsistent use of -mcpu and -march.
> +
> + // If we have -mcpu=, use that.
> + if (Arg *A = Args.getLastArg(options::OPT_mcpu_EQ)) {
> + StringRef MCPU = A->getValue();
> + // Handle -mcpu=native.
> + if (MCPU == "native")
> + return llvm::sys::getHostCPUName();
> + else
> + return MCPU;
> + }
> +
> + return "generic";
> +}
> +
> // FIXME: Move to target hook.
> static bool isSignedCharDefault(const llvm::Triple &Triple) {
> switch (Triple.getArch()) {
> @@ -1304,6 +1324,9 @@ static std::string getCPUName(const ArgL
> default:
> return "";
>
> + case llvm::Triple::aarch64:
> + return getAArch64TargetCPU(Args, T);
> +
> case llvm::Triple::arm:
> case llvm::Triple::thumb:
> return getARMTargetCPU(Args, T);
>
> Modified: cfe/trunk/lib/Driver/Tools.h
> URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Driver/Tools.h?rev=193740&r1=193739&r2=193740&view=diff
>
> ==============================================================================
> --- cfe/trunk/lib/Driver/Tools.h (original)
> +++ cfe/trunk/lib/Driver/Tools.h Thu Oct 31 04:32:33 2013
> @@ -49,6 +49,8 @@ using llvm::opt::ArgStringList;
> const InputInfo &Output,
> const InputInfoList &Inputs) const;
>
> + void AddAArch64TargetArgs(const llvm::opt::ArgList &Args,
> + llvm::opt::ArgStringList &CmdArgs) const;
> void AddARMTargetArgs(const llvm::opt::ArgList &Args,
> llvm::opt::ArgStringList &CmdArgs,
> bool KernelOrKext) const;
>
> Added: cfe/trunk/test/Driver/aarch64-cpus.c
> URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Driver/aarch64-cpus.c?rev=193740&view=auto
>
> ==============================================================================
> --- cfe/trunk/test/Driver/aarch64-cpus.c (added)
> +++ cfe/trunk/test/Driver/aarch64-cpus.c Thu Oct 31 04:32:33 2013
> @@ -0,0 +1,10 @@
> +// Check target CPUs are correctly passed.
> +
> +// RUN: %clang -target aarch64 -### -c %s 2>&1 | FileCheck
> -check-prefix=GENERIC %s
> +// GENERIC: "-cc1"{{.*}} "-triple" "aarch64" {{.*}} "-target-cpu"
> "generic"
> +
> +// RUN: %clang -target aarch64 -mcpu=cortex-a53 -### -c %s 2>&1 |
> FileCheck -check-prefix=CA53 %s
> +// CA53: "-cc1"{{.*}} "-triple" "aarch64" {{.*}} "-target-cpu"
> "cortex-a53"
> +
> +// RUN: %clang -target aarch64 -mcpu=cortex-a57 -### -c %s 2>&1 |
> FileCheck -check-prefix=CA57 %s
> +// CA57: "-cc1"{{.*}} "-triple" "aarch64" {{.*}} "-target-cpu"
> "cortex-a57"
>
> Added: cfe/trunk/test/Driver/aarch64-mfpu.c
> URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Driver/aarch64-mfpu.c?rev=193740&view=auto
>
> ==============================================================================
> --- cfe/trunk/test/Driver/aarch64-mfpu.c (added)
> +++ cfe/trunk/test/Driver/aarch64-mfpu.c Thu Oct 31 04:32:33 2013
> @@ -0,0 +1,26 @@
> +// Test that different values of -mfpu pick correct AArch64 FPU
> target-feature(s).
> +
> +// RUN: %clang -target aarch64-linux-eabi -mfpu=neon %s -### -o %t.o 2>&1
> \
> +// RUN: | FileCheck --check-prefix=CHECK-NEON %s
> +// CHECK-NEON: "-target-feature" "+neon"
> +
> +// RUN: %clang -target aarch64-linux-eabi -mfpu=fp-armv8 %s -### -o %t.o
> 2>&1 \
> +// RUN: | FileCheck --check-prefix=CHECK-FP-ARMV8 %s
> +// CHECK-FP-ARMV8: "-target-feature" "+fp-armv8"
> +
> +// RUN: %clang -target aarch64-linux-eabi -mfpu=neon-fp-armv8 %s -###
> 2>&1 \
> +// RUN: | FileCheck --check-prefix=CHECK-NEON-FP-ARMV8 %s
> +// CHECK-NEON-FP-ARMV8: "-target-feature" "+fp-armv8"
> +// CHECK-NEON-FP-ARMV8: "-target-feature" "+neon"
> +
> +// RUN: %clang -target aarch64-linux-eabi -mfpu=crypto-neon-fp-armv8 %s
> -### 2>&1 \
> +// RUN: | FileCheck --check-prefix=CHECK-CRYPTO-NEON-FP-ARMV8 %s
> +// CHECK-CRYPTO-NEON-FP-ARMV8: "-target-feature" "+fp-armv8"
> +// CHECK-CRYPTO-NEON-FP-ARMV8: "-target-feature" "+neon"
> +// CHECK-CRYPTO-NEON-FP-ARMV8: "-target-feature" "+crypto"
> +
> +// RUN: %clang -target aarch64-linux-eabi -mfpu=none %s -### 2>&1 \
> +// RUN: | FileCheck --check-prefix=CHECK-NO-FP %s
> +// CHECK-NO-FP: "-target-feature" "-fp-armv8"
> +// CHECK-NO-FP: "-target-feature" "-crypto"
> +// CHECK-NO-FP: "-target-feature" "-neon"
>
>
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