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[llvm][AArch64] apple-m4 is armv9.2-a #98267

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Merged
merged 7 commits into from
Jul 11, 2024
Merged

[llvm][AArch64] apple-m4 is armv9.2-a #98267

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2ca4c25
[llvm][AArch64] apple-m4 is armv9.2-a
jroelofs Jul 10, 2024
7253170
clang-format
jroelofs Jul 10, 2024
f8df80a
FEAT_MEC is optional in v9.2, FEAT_RME is optional in v9.1
jroelofs Jul 10, 2024
220d26c
clang-format
jroelofs Jul 10, 2024
4b98185
clang-format some more. the bot's version must be different than mine
jroelofs Jul 10, 2024
da1225d
Merge branch 'main' into jroelofs/apple-m4-is-v9p2
jroelofs Jul 10, 2024
70c44ea
rme and mec are optional, fix tests
jroelofs Jul 10, 2024
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8 changes: 2 additions & 6 deletions llvm/include/llvm/TargetParser/AArch64TargetParser.h
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Original file line number Diff line number Diff line change
Expand Up @@ -161,14 +161,10 @@ struct CpuInfo {
StringRef Name; // Name, as written for -mcpu.
const ArchInfo &Arch;
AArch64::ExtensionBitset
DefaultExtensions; // Default extensions for this CPU. These will be
// ORd with the architecture defaults.
DefaultExtensions; // Default extensions for this CPU.

AArch64::ExtensionBitset getImpliedExtensions() const {
AArch64::ExtensionBitset ImpliedExts;
ImpliedExts |= DefaultExtensions;
ImpliedExts |= Arch.DefaultExts;
return ImpliedExts;
return DefaultExtensions;
Comment on lines -168 to +167
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IIUC, the idea here is that we don't want to add the architecture's default extensions to the CPU, because they are not mandatory, and there's no way to disable them for a CPU that chooses not to implement. This is why all the CPUs have had their list of features expanded.

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Yes, and that idea is the problem: automatically adding default extensions kinda works for extensions that the compiler doesn't generate automatically where their use is driven by intrinsics, but as soon as you have something like SVE in the list you get incompatible codegen left and right.

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This choice also makes -march= meaningless, so @ahmedbougacha and I are considering making that an error at least on Darwin platforms.

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Not sure I follow... Do you mean -march= has no effect if you specify -mcpu? That should probably be at least a warning.

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@jroelofs jroelofs Jul 12, 2024 •
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I mean that code built with -march=armv9.2a may use SVE instructions because FeatureSVE is in the default list for v9.0, but this will crash on an M4 iPad.

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for example: https://clang.godbolt.org/z/4jW8nqK41

}
};

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2 changes: 1 addition & 1 deletion llvm/lib/Target/AArch64/AArch64Features.td
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Expand Up @@ -797,7 +797,7 @@ def HasV8_9aOps : Architecture64<8, 9, "a", "v8.9a",
!listconcat(HasV8_8aOps.DefaultExts, [FeatureSPECRES2, FeatureCSSC,
FeatureRASv2])>;
def HasV9_0aOps : Architecture64<9, 0, "a", "v9a",
[HasV8_5aOps, FeatureMEC],
[HasV8_5aOps],
!listconcat(HasV8_5aOps.DefaultExts, [FeatureFullFP16, FeatureSVE,
FeatureSVE2])>;
def HasV9_1aOps : Architecture64<9, 1, "a", "v9.1a",
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