[LTO] Set default Darwin CPU to apple-a7 for AArch64

[AtariDreams]

Use apple-a7 as default for AArch64 Darwin targets that are not arm64e, as apple-a7 is the first AArch64 CPU that can run Darwin.

[llvmbot]

@llvm/pr-subscribers-backend-arm
@llvm/pr-subscribers-backend-aarch64
@llvm/pr-subscribers-llvm-globalisel
@llvm/pr-subscribers-llvm-binary-utilities

@llvm/pr-subscribers-lto

Author: AtariDreams (AtariDreams)

Changes

Use apple-a7 as default for AArch64 Darwin targets that are not arm64e, as apple-a7 is the first AArch64 CPU that can run Darwin.

---

Full diff: https://github.com/llvm/llvm-project/pull/81540.diff

2 Files Affected:

• (modified) llvm/lib/LTO/LTOCodeGenerator.cpp (+3-2)
• (modified) llvm/lib/LTO/ThinLTOCodeGenerator.cpp (+5-2)

diff --git a/llvm/lib/LTO/LTOCodeGenerator.cpp b/llvm/lib/LTO/LTOCodeGenerator.cpp
index 52d8fff14be9ce..93fdde9c9b1d97 100644
--- a/llvm/lib/LTO/LTOCodeGenerator.cpp
+++ b/llvm/lib/LTO/LTOCodeGenerator.cpp
@@ -417,8 +417,9 @@ bool LTOCodeGenerator::determineTarget() {
       Config.CPU = "yonah";
     else if (Triple.isArm64e())
       Config.CPU = "apple-a12";
-    else if (Triple.getArch() == llvm::Triple::aarch64 ||
-             Triple.getArch() == llvm::Triple::aarch64_32)
+    else if (Triple.getArch() == llvm::Triple::aarch64)
+      Config.MCpu = "apple-a7";
+    else if (Triple.getArch() == llvm::Triple::aarch64_32)
       Config.CPU = "cyclone";
   }
 
diff --git a/llvm/lib/LTO/ThinLTOCodeGenerator.cpp b/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
index 535faf5f780474..1c58cef5c3dc8d 100644
--- a/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
+++ b/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
@@ -546,8 +546,11 @@ static void initTMBuilder(TargetMachineBuilder &TMBuilder,
       TMBuilder.MCpu = "core2";
     else if (TheTriple.getArch() == llvm::Triple::x86)
       TMBuilder.MCpu = "yonah";
-    else if (TheTriple.getArch() == llvm::Triple::aarch64 ||
-             TheTriple.getArch() == llvm::Triple::aarch64_32)
+    else if (TheTriple.isArm64e())
+      TMBuilder.MCpu = "apple-a12";
+    else if (TheTriple.getArch() == llvm::Triple::aarch64)
+      TMBuilder.MCpu = "apple-a7";
+    else if (TheTriple.getArch() == llvm::Triple::aarch64_32)
       TMBuilder.MCpu = "cyclone";
   }
   TMBuilder.TheTriple = std::move(TheTriple);

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[cachemeifyoucan]

I think cyclone and apple-a7 is the same CPU (see AArch64.td). If we are going to rename default to a well-known name, might as well rename aarch64_32 as well.

[jroelofs]

I think cyclone and apple-a7 is the same CPU (see AArch64.td).

Yes.

If we are going to rename default to a well-known name, might as well rename aarch64_32 as well.

Agreed. We should prefer the apple-a* names over their weather-event-ish aliases.

[jroelofs]

This is a functional change, and should come with a test.

[jroelofs]

@ahmedbougacha fyi, I think we're missing this one ^

[jroelofs]

@AtariDreams please stop resolving this

[fhahn]

Note that for ARM64 macOS the default CPU is apple-m1 instead. While you are here, it would probably be worth adjusting that also (see https://github.com/llvm/llvm-project/blob/main/clang/lib/Driver/ToolChains/Arch/AArch64.cpp#L50)

There probably should be a helper function to return the default CPU string and have it used at least for all llvm/lib/LTO changes, possibly also in Clang, to prevent those things from drifting apart in the future again.