[Driver][Darwin] Use Host Triple to infer target os version

[steven_wu]

Summary

When clang required to infer target os version from --target option and
the os version is not specified in targets, check the host triple. If the
host and target are both macOS, use host triple to infer target os
version.

rdar://problem/41651999

[steven_wu]

Unfortunately, I wasn't able to write a test for this because the host triple in the configuration can either be x86_64-apple-darwin* or x86_64-apple-macosx*, but the one used passed by driver is always macosx one. I can't reliably compare those two.

[steven_wu]

Update patch. Use a better API.

[steven_wu]

Rebase the commit correctly

[arphaman]

Hmm, the driver should not call inferDeploymentTargetFromArch when -target is passed. Or am I missing something?

[steven_wu]

In D48849#1150246, @arphaman wrote:

Hmm, the driver should not call inferDeploymentTargetFromArch when -target is passed. Or am I missing something?

Good call. This only handles the *-apple-darwin case. Maybe the same should happen to *-apple-macosx.

[steven_wu]

handle *-apple-macosx target option

[arphaman]

Nit: Could you please try to extract the shared code into a function, e.g.

Optional<std::string> overrideMacOSTripleDefaultVersion(const llvm::Triple &Triple, ... OSTy, ... TheDriver) {
    if (Triple.getOSMajorVersion())
      return None;
    llvm::Triple SystemTriple(llvm::sys::getProcessTriple());
    if (SystemTriple.isMacOSX())
      return getOSVersion(OSTy, SystemTriple, TheDriver));
   return None;
}

[steven_wu]

It is easier and cleaner if I just fold everything into getOSVersion.

[arphaman]

LGTM

lib/Driver/ToolChains/Darwin.cpp

inferDeploymentTargetFromArch(DerivedArgList &Args, const Darwin &Toolchain,
 
   StringRef MachOArchName = Toolchain.getMachOArchName(Args);
   if (MachOArchName == "armv7" || MachOArchName == "armv7s" ||
       MachOArchName == "arm64")
     OSTy = llvm::Triple::IOS;
   else if (MachOArchName == "armv7k")
     OSTy = llvm::Triple::WatchOS;
   else if (MachOArchName != "armv6m" && MachOArchName != "armv7m" &&
-           MachOArchName != "armv7em")
+           MachOArchName != "armv7em") {
+    // Default to macOS for other architectures.
     OSTy = llvm::Triple::MacOSX;
 
+    // If there is no version specified on triple, and both host and target are
+    // macos, use the host triple to infer OS version.
+    llvm::Triple SystemTriple(llvm::sys::getProcessTriple());
+    if (SystemTriple.isMacOSX() && !Triple.getOSMajorVersion())
+      return DarwinPlatform::createFromArch(
+          OSTy, getOSVersion(OSTy, SystemTriple, TheDriver));
+  }
+
   if (OSTy == llvm::Triple::UnknownOS)
     return None;
   return DarwinPlatform::createFromArch(OSTy,
                                         getOSVersion(OSTy, Triple, TheDriver));
 }
 
 /// Returns the deployment target that's specified using the -target option.
 Optional<DarwinPlatform> getDeploymentTargetFromTargetArg(

test/Driver/clang-g-opts.c

 // RUN: %clang -### -S %s        2>&1 | FileCheck --check-prefix=CHECK-WITHOUT-G %s
 // RUN: %clang -### -S %s -g -target x86_64-linux-gnu 2>&1 \
 // RUN:             | FileCheck --check-prefix=CHECK-WITH-G %s
 
 // Assert that the toolchains which should default to a lower Dwarf version do so.
-// RUN: %clang -### -S %s -g -target x86_64-apple-darwin 2>&1 \
+// RUN: %clang -### -S %s -g -target x86_64-apple-darwin8 2>&1 \
 // RUN:             | FileCheck --check-prefix=CHECK-WITH-G-DWARF2 %s
 // RUN: %clang -### -S %s -g -target i686-pc-openbsd 2>&1 \
 // RUN:             | FileCheck --check-prefix=CHECK-WITH-G-DWARF2 %s
 // RUN: %clang -### -S %s -g -target x86_64-pc-freebsd10.0 2>&1 \
 // RUN:             | FileCheck --check-prefix=CHECK-WITH-G-DWARF2 %s
 
 // 'g0' is the default. Just sanity-test that it does nothing
 // RUN: %clang -### -S %s -g0    2>&1 | FileCheck --check-prefix=CHECK-WITHOUT-G %s
 
 // And check that the last of -g or -g0 wins.
 // RUN: %clang -### -S %s -g -g0 2>&1 | FileCheck --check-prefix=CHECK-WITHOUT-G %s
 
 // These should be semantically the same as not having given 'g0' at all,
 // as the last 'g' option wins.
 //
 // RUN: %clang -### -S %s -g0 -g -target x86_64-linux-gnu 2>&1 \
 // RUN:             | FileCheck --check-prefix=CHECK-WITH-G %s
-// RUN: %clang -### -S %s -g0 -g -target x86_64-apple-darwin 2>&1 \
+// RUN: %clang -### -S %s -g0 -g -target x86_64-apple-darwin8 2>&1 \
 // RUN:             | FileCheck --check-prefix=CHECK-WITH-G-STANDALONE %s
 // RUN: %clang -### -S %s -g0 -g -target i686-pc-openbsd 2>&1 \
 // RUN:             | FileCheck --check-prefix=CHECK-WITH-G-DWARF2 %s
 // RUN: %clang -### -S %s -g0 -g -target x86_64-pc-freebsd10.0 2>&1 \
 // RUN:             | FileCheck --check-prefix=CHECK-WITH-G-DWARF2 %s
 // RUN: %clang -### -S %s -g0 -g -target i386-pc-solaris 2>&1 \
 // RUN:             | FileCheck --check-prefix=CHECK-WITH-G-DWARF2 %s
 
 // CHECK-WITHOUT-G-NOT: -debug-info-kind
 // CHECK-WITH-G: "-debug-info-kind=limited"
 // CHECK-WITH-G: "-dwarf-version=4"
 // CHECK-WITH-G-DWARF2: "-dwarf-version=2"
 
 // CHECK-WITH-G-STANDALONE: "-debug-info-kind=standalone"
 // CHECK-WITH-G-STANDALONE: "-dwarf-version=2"