[Utility] Fix ArchSpec.MergeFrom to correctly merge environments

[xiaobai]

Summary

This behavior was originally added in rL252264 (git commit 76a7f365da)
in order to be extra careful with handling platforms like watchos and tvos.
However, as far as triples go, those two (and others) are treated as OSes and
not environments, so that should not really apply here.

Additionally, this behavior is incorrect and can lead to incorrect ArchSpecs.
Because android is specified as an environment and not an OS, not propogating
the environment can lead to modules and targets being misidentified.

[xiaobai]

Accidentally added a commit to this diff that I didn't intend to add.

[aprantl]

Could you please add more context to the diff? Something like git diff -U9999 HEAD~1 works fine.

[xiaobai]

In D58664#1410750, @aprantl wrote:

Could you please add more context to the diff? Something like git diff -U9999 HEAD~1 works fine.

Will do. It looks like the dependent diff might change significantly so I'm going to rebase this on top of master instead since the functionality isn't technically tied to the dependent diff.

[xiaobai]

More context + rebase on top of master

[xiaobai]

Rebase on master

source/Utility/ArchSpec.cpp

if (GetTriple().getArch() == llvm::Triple::UnknownArch) {
 
     // MachO unknown64 isn't really invalid as the debugger can still obtain
     // information from the binary, e.g. line tables. As such, we don't update
     // the core here.
     if (other.GetCore() != eCore_uknownMach64)
       UpdateCore();
   }
   if (!TripleEnvironmentWasSpecified() &&
-      other.TripleEnvironmentWasSpecified() && !TripleVendorWasSpecified()) {
-    if (other.TripleVendorWasSpecified())
-      GetTriple().setEnvironment(other.GetTriple().getEnvironment());
+      other.TripleEnvironmentWasSpecified()) {
   }
   // If this and other are both arm ArchSpecs and this ArchSpec is a generic
   // "some kind of arm" spec but the other ArchSpec is a specific arm core,
   // adopt the specific arm core.
   if (GetTriple().getArch() == llvm::Triple::arm &&
       other.GetTriple().getArch() == llvm::Triple::arm &&
       IsCompatibleMatch(other) && GetCore() == ArchSpec::eCore_arm_generic &&
       other.GetCore() != ArchSpec::eCore_arm_generic) {

unittests/Utility/ArchSpecTest.cpp

TEST(ArchSpecTest, TestSetTriple) {
   AS = ArchSpec();
   EXPECT_FALSE(AS.SetTriple("unknown"));
 
   AS = ArchSpec();
   EXPECT_FALSE(AS.SetTriple(""));
 }
 
 TEST(ArchSpecTest, MergeFrom) {
+  {
     ArchSpec A;
     ArchSpec B("x86_64-pc-linux");
 
     EXPECT_FALSE(A.IsValid());
     ASSERT_TRUE(B.IsValid());
     EXPECT_EQ(llvm::Triple::ArchType::x86_64, B.GetTriple().getArch());
     EXPECT_EQ(llvm::Triple::VendorType::PC, B.GetTriple().getVendor());
     EXPECT_EQ(llvm::Triple::OSType::Linux, B.GetTriple().getOS());
     EXPECT_EQ(ArchSpec::eCore_x86_64_x86_64, B.GetCore());
 
     A.MergeFrom(B);
     ASSERT_TRUE(A.IsValid());
     EXPECT_EQ(llvm::Triple::ArchType::x86_64, A.GetTriple().getArch());
     EXPECT_EQ(llvm::Triple::VendorType::PC, A.GetTriple().getVendor());
     EXPECT_EQ(llvm::Triple::OSType::Linux, A.GetTriple().getOS());
     EXPECT_EQ(ArchSpec::eCore_x86_64_x86_64, A.GetCore());
   }
+  {
+    ArchSpec A("aarch64");
+    ArchSpec B("aarch64--linux-android");
+
+    EXPECT_TRUE(A.IsValid());
+    EXPECT_TRUE(B.IsValid());
+
+    EXPECT_EQ(llvm::Triple::ArchType::aarch64, B.GetTriple().getArch());
+    EXPECT_EQ(llvm::Triple::VendorType::UnknownVendor,
+              B.GetTriple().getVendor());
+    EXPECT_EQ(llvm::Triple::OSType::Linux, B.GetTriple().getOS());
+    EXPECT_EQ(llvm::Triple::EnvironmentType::Android,
+              B.GetTriple().getEnvironment());
+
+    A.MergeFrom(B);
+    EXPECT_EQ(llvm::Triple::ArchType::aarch64, A.GetTriple().getArch());
+    EXPECT_EQ(llvm::Triple::VendorType::UnknownVendor,
+              A.GetTriple().getVendor());
+    EXPECT_EQ(llvm::Triple::OSType::Linux, A.GetTriple().getOS());
+    EXPECT_EQ(llvm::Triple::EnvironmentType::Android,
+              A.GetTriple().getEnvironment());
+  }
+}
 
 TEST(ArchSpecTest, MergeFromMachOUnknown) {
   class MyArchSpec : public ArchSpec {
   public:
     MyArchSpec() {
       this->SetTriple("unknown-mach-64");
       this->m_core = ArchSpec::eCore_uknownMach64;
       this->m_byte_order = eByteOrderLittle;