[Clang,Driver] Default to Darwin_libsystem_m veclib on iOS based targets.

[fhahn]

Summary

Building on D102489, default to Darwin_libsystem_m veclib on iOS based
targets.

[arphaman]

clang/lib/Driver/ToolChains/Darwin.cpp

2492

Is this applicable to the watchOS targets as well? The iOS based check doesn't cover it.

clang/test/Driver/darwin-veclib-default.c

9

darwinos isn't a valid OS type, what's your intent with this testcase here?

[fhahn]

clang/lib/Driver/ToolChains/Darwin.cpp

2492

libsystem_m's vector functions should be available on all Darwin platforms I think. I'd gradually opt-in additional platforms, once we verified it is clearly beneficial for each platform individually.

Should I add a TODO?

clang/test/Driver/darwin-veclib-default.c

9

Ah OK! Would it make sense to check -darwin? Or just -iOS?

[scanon]

clang/lib/Driver/ToolChains/Darwin.cpp

2492

Correct, available on all Darwin systems. These APIs were introduced in macOS 10.13, iOS 11.0, watchOS 4.0, tvOS 11.0, and driverkit 19.0. I think we need a check that the target is at least those versions somewhere?

[arphaman]

clang/lib/Driver/ToolChains/Darwin.cpp

2492

Yes we should check if the target version is supported in the Driver and error out if it's used for an earlier OS.

2492

Sure, a FIXME comment for the other platform support is fine for now.

clang/test/Driver/darwin-veclib-default.c

9

Just ios. You're already checking darwin above.

[fhahn]

We are still evaluating whether it is safe to use this as default. I'll mark it as 'changes planned' for now.

[fhahn]

As of now, I don't think this is safe to do with the precision guarantees Darwin_libsystem_m provides unfortunately.

clang/lib/Driver/ToolChains/Darwin.cpp

void Darwin::addClangTargetOptions(const llvm::opt::ArgList &DriverArgs,
   CC1Args.push_back("-fcompatibility-qualified-id-block-type-checking");
 
   // Give static local variables in inline functions hidden visibility when
   // -fvisibility-inlines-hidden is enabled.
   if (!DriverArgs.getLastArgNoClaim(
           options::OPT_fvisibility_inlines_hidden_static_local_var,
           options::OPT_fno_visibility_inlines_hidden_static_local_var))
     CC1Args.push_back("-fvisibility-inlines-hidden-static-local-var");
+
+  // If no vector library is specified by the user, default to
+  // Darwin_libsystem_m for iOS based targets.
+  if (isTargetIOSBased() && !DriverArgs.hasArgNoClaim(options::OPT_fveclib))
+    CC1Args.push_back("-fveclib=Darwin_libsystem_m");
 }
 
 DerivedArgList *
 Darwin::TranslateArgs(const DerivedArgList &Args, StringRef BoundArch,
                       Action::OffloadKind DeviceOffloadKind) const {
   // First get the generic Apple args, before moving onto Darwin-specific ones.
   DerivedArgList *DAL =
       MachO::TranslateArgs(Args, BoundArch, DeviceOffloadKind);

clang/test/Driver/darwin-veclib-default.c

+// Check default vector library options on Darwin platforms.
+
+// RUN: %clang -target x86_64-apple-darwin -S -### %s -arch x86_64 2>&1 | \
+// RUN:   FileCheck --check-prefix CHECK-MACOS %s
+
+// CHECK-MACOS: "-cc1"
+// CHECK-MACOS-NOT: -fveclib
+
+// RUN: %clang -target arm64-apple-darwinos -S -### %s -arch arm64 2>&1 | \
+// RUN:   FileCheck --check-prefix CHECK-IOS-DEFAULT %s
+
+// RUN: %clang -target arm64-apple-ios -S -### %s -arch arm64 2>&1 | \
+// RUN:   FileCheck --check-prefix CHECK-IOS-DEFAULT %s
+
+// CHECK-IOS-DEFAULT: "-cc1"
+// CHECK-IOS-DEFAULT: "-fveclib=Darwin_libsystem_m"
+
+// RUN: %clang -target arm64-apple-ios -S -### %s -arch arm64 -fveclib=Accelerate 2>&1 | \
+// RUN:   FileCheck --check-prefix CHECK-IOS-ACCELERATE %s
+
+// CHECK-IOS-ACCELERATE: "-cc1"
+// CHECK-IOS-ACCELERATE-NOT: "-fveclib=Darwin_libsystem_m"
+// CHECK-IOS-ACCELERATE: "-fveclib=Accelerate"
+// CHECK-IOS-ACCELERATE-NOT: "-fveclib=Darwin_libsystem_m"