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[AArch64] Bump default CPUs for iOS 26/watchOS 26 to A12/S6. #152235

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Merged
merged 2 commits into from
Aug 11, 2025
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[AArch64] Bump default CPUs for iOS 26/watchOS 26 to A12/S6. #152235

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16b2542
[AArch64] Bump default CPUs for iOS 26/watchOS 26 to A12/S6.
ahmedbougacha Aug 5, 2025
34cfb56
Fix test comment formatting.
ahmedbougacha Aug 6, 2025
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16 changes: 16 additions & 0 deletions clang/lib/Driver/ToolChains/Arch/AArch64.cpp
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Expand Up @@ -52,6 +52,22 @@ std::string aarch64::getAArch64TargetCPU(const ArgList &Args,
return "apple-m1";
}

if (Triple.getOS() == llvm::Triple::IOS) {
assert(!Triple.isSimulatorEnvironment() && "iossim should be mac-like");
// iOS 26 only runs on apple-a12 and later CPUs.
if (!Triple.isOSVersionLT(26))
return "apple-a12";
}
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what about the two other places in the LTO backend where we do this sort of platform default thing?

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Ah right, I think of those as a remnant of early LTO support, a default fallback for cases where the frontend doesn't set up the target IR attributes.
The last addition was arm64e/a12, when we still had unattributed functions, in obscure corners of clang IRGen that synthesize thunks and wrappers. I'd expect those to be thoroughly eliminated now, after the waves of ptrauth attribute variations that will break if missing, and can't rely on this sort of late fallback.

So I'd say we could probably try to remove the LTO logic altogether, at the risk of breaking some library users without a clang-equivalent driver.
There's a case to be made this logic should be an llvm default backing a driver override, which would help other users. I don't think that's a bad idea, and it seems it'd belong in TargetParser? But overall I think it's just another on the long list of low-level choices that clang has to do and are hard to separate; using clang seems unavoidable (also see Jordan and John's old llvm devmtg talk "Skip the FFI" ;)

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Related: at some point we discussed having a way of describing default function attributes in a module (e.g., using module flags), for cases where functions are generated later that IRGen, in the IR pipeline. Of course I can't find any links anymore, but I'd expect those to have another (frontend-IRGen'd) function to use as a template. Of course one can imagine some hypothetical transform where that isn't true ;)


if (Triple.isWatchOS()) {
assert(!Triple.isSimulatorEnvironment() && "watchossim should be mac-like");
// arm64_32/arm64e watchOS requires S4 before watchOS 26, S6 after.
if (Triple.getArch() == llvm::Triple::aarch64_32 || Triple.isArm64e())
return Triple.isOSVersionLT(26) ? "apple-s4" : "apple-s6";
Comment on lines +65 to +66
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Suggested change
if (Triple.getArch() == llvm::Triple::aarch64_32 || Triple.isArm64e())
return Triple.isOSVersionLT(26) ? "apple-s4" : "apple-s6";
if ((Triple.getArch() == llvm::Triple::aarch64_32 || Triple.isArm64e()) &&
Triple.isOSVersionLT(26))
return "apple-s4";

Maybe? Seems nicer to avoid nested conditionals, but not a strong opinion.

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Yeah, that could be a sensible alternative, but I tried to keep it structured in a way that keeps each policy clearly delineated: in this case there are distinct reasons we end up with S6; the same applies later for the various ways we end up with A12.

// arm64 (non-e, non-32) watchOS comes later, and requires S6 anyway.
return "apple-s6";
}

if (Triple.isXROS()) {
// The xrOS simulator runs on M1 as well, it should have been covered above.
assert(!Triple.isSimulatorEnvironment() && "xrossim should be mac-like");
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22 changes: 22 additions & 0 deletions clang/test/Driver/aarch64-cpu-defaults-appleos26.c
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@@ -0,0 +1,22 @@
/// iOS 26 and watchOS 26 bump the default arm64 CPU targets.

/// arm64 iOS 26 defaults to apple-a12. arm64e already did.
// RUN: %clang -target arm64-apple-ios26 -### -c %s 2>&1 | FileCheck %s --check-prefix=A12
// RUN: %clang -target arm64e-apple-ios26 -### -c %s 2>&1 | FileCheck %s --check-prefix=A12

// arm64e/arm64_32 watchOS 26 default to apple-s6.
// RUN: %clang -target arm64e-apple-watchos26 -### -c %s 2>&1 | FileCheck %s --check-prefix=S6
// RUN: %clang -target arm64_32-apple-watchos26 -### -c %s 2>&1 | FileCheck %s --check-prefix=S6

// arm64 is new in watchOS 26, and defaults to apple-s6.
// RUN: %clang -target arm64-apple-watchos26 -### -c %s 2>&1 | FileCheck %s --check-prefix=S6

/// llvm usually treats tvOS like iOS, but it runs on different hardware.
// RUN: %clang -target arm64-apple-tvos26 -### -c %s 2>&1 | FileCheck %s --check-prefix=A7
// RUN: %clang -target arm64e-apple-tvos26 -### -c %s 2>&1 | FileCheck %s --check-prefix=A12

/// Simulators are tested with other Mac-like targets in aarch64-mac-cpus.c.

// A12: "-target-cpu" "apple-a12"
// S6: "-target-cpu" "apple-s6"
// A7: "-target-cpu" "apple-a7"
2 changes: 1 addition & 1 deletion clang/test/Driver/aarch64-mac-cpus.c
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@@ -1,4 +1,4 @@
// arm64 Mac-based targets default to Apple A13.
// arm64/arm64e Mac-based targets default to Apple M1.

// RUN: %clang --target=arm64-apple-macos -### -c %s 2>&1 | FileCheck %s
// RUN: %clang --target=arm64-apple-ios-macabi -### -c %s 2>&1 | FileCheck %s
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