MC: Warn on .xxx_version_min <-> target triple version mismatch

[MatzeB]

Summary

Warn if the .{ios|tvos|macosx|watchos}_version_min version does not match the target triple.

[t.p.northover]

This might be a bit overzealous. A simple "clang -arch armv7s myfile.s" defaults to an ios5.0 triple rather than an unspecified version, but I'd prefer not to have to tell clang both on the command-line and in a directive about the version (and to have to keep them in sync).

[MatzeB]

In D14999#296979, @t.p.northover wrote:

This might be a bit overzealous. A simple "clang -arch armv7s myfile.s" defaults to an ios5.0 triple rather than an unspecified version, but I'd prefer not to have to tell clang both on the command-line and in a directive about the version (and to have to keep them in sync).

The intention was to not perform the check if no version was specified on the commandline, but if there is no way to tell if we have an explicitely specified version or a default in the target triple for the "clang -cc1as" invocation, then I guess there is no way to produce a warning without false positives here.

lib/MC/MCParser/DarwinAsmParser.cpp

bool DarwinAsmParser::parseVersionMin(StringRef Directive, SMLoc Loc) {
   const Triple &T = getContext().getObjectFileInfo()->getTargetTriple();
   Triple::OSType ExpectedOS = Triple::UnknownOS;
   switch ((MCVersionMinType)Kind) {
   case MCVM_WatchOSVersionMin: ExpectedOS = Triple::WatchOS; break;
   case MCVM_TvOSVersionMin:    ExpectedOS = Triple::TvOS;    break;
   case MCVM_IOSVersionMin:     ExpectedOS = Triple::IOS;     break;
   case MCVM_OSXVersionMin:     ExpectedOS = Triple::MacOSX;  break;
   }
-  if (T.getOS() != ExpectedOS)
+  if (T.getOS() != ExpectedOS) {
     Warning(Loc, Directive + " should only be used for " +
             Triple::getOSTypeName(ExpectedOS) + " targets");
+  } else {
+    // Check if target triple version matches the one in the directive.
+    unsigned TripleMajor, TripleMinor, TripleMicro;
+    T.getOSVersion(TripleMajor, TripleMinor, TripleMicro);
+    if ((TripleMajor != 0 || TripleMinor != 0 || TripleMicro != 0) &&
+        (Major != TripleMajor || Minor != TripleMinor ||
+         (Update != 0 && TripleMicro != 0 && Update != TripleMicro))) {
+      Warning(Loc, Twine(Directive) + " " + Twine(Major) + "," + Twine(Minor) +
+              "," + Twine(Update) + " does not match target version " +
+              Twine(TripleMajor) + "," + Twine(TripleMinor) + "," +
+              Twine(TripleMicro));
+    }
+  }
 
   if (LastVersionMinDirective.isValid()) {
     Warning(Loc, "overriding previous version_min directive");
     Note(LastVersionMinDirective, "previous definition is here");
   }
   LastVersionMinDirective = Loc;
 
   // We've parsed a correct version specifier, so send it to the streamer.

test/MC/MachO/ARM/version-min-diagnostics3.s

+// RUN: llvm-mc -triple armv7s-apple-ios %s 2>&1 | FileCheck --check-prefix=CHECK --check-prefix=VNONE %s
+// RUN: llvm-mc -triple armv7s-apple-ios9.0.1 %s 2>&1 | FileCheck --check-prefix=CHECK --check-prefix=VNINE --check-prefix=VNINE_MICRO %s
+// RUN: llvm-mc -triple armv7s-apple-ios9.0 %s 2>&1 | FileCheck --check-prefix=CHECK --check-prefix=VNINE --check-prefix=VNINE_NOMICRO %s
+
+// VNONE-NOT: version-min-diagnostics3.s:[[@LINE+2]]{{.*}}does not match target version
+// VNINE: version-min-diagnostics3.s:[[@LINE+1]]:1: warning: .ios_version_min 8,0,0 does not match target version 9,
+.ios_version_min 8,0
+// VNONE-NOT: version-min-diagnostics3.s:[[@LINE+2]]{{.*}}does not match target version
+// VNINE: version-min-diagnostics3.s:[[@LINE+1]]:1: warning: .ios_version_min 10,0,0 does not match target version 9,
+.ios_version_min 10,0
+// VNONE-NOT: version-min-diagnostics3.s:[[@LINE+2]]{{.*}}does not match target version
+// VNINE: version-min-diagnostics3.s:[[@LINE+1]]:1: warning: .ios_version_min 9,1,0 does not match target version 9,
+.ios_version_min 9,1
+// VNONE-NOT: version-min-diagnostics3.s:[[@LINE+3]]{{.*}}does not match target version
+// VNINE_NOMICRO-NOT: version-min-diagnostics3.s:[[@LINE+2]]{{.*}}does not match target version
+// VNINE_MICRO: version-min-diagnostics3.s:[[@LINE+1]]:1: warning: .ios_version_min 9,0,2 does not match target version 9,0,1
+.ios_version_min 9,0,2
+
+// CHECK-NOT: version-min-diagnostics3.s:[[@LINE+1]]{{.*}}does not match target version
+.ios_version_min 9,0
+// CHECK-NOT: version-min-diagnostics3.s:[[@LINE+1]]{{.*}}does not match target version
+.ios_version_min 9,0,1