[TargetParser] Check size before accessing architecture version.

[fhahn]

Summary

This fixes a crash when invalid -march options like armv are provided.

Based on a patch by Will Lovett.

[samparker]

Thanks, LGTM.

lib/Support/TargetParser.cpp

for (const auto &CPU : AArch64CPUNames)
     if (CPU.ArchID == AK && CPU.Default)
       return CPU.getName();
 
   // If we can't find a default then target the architecture instead
   return "generic";
 }
 
 unsigned llvm::AArch64::checkArchVersion(StringRef Arch) {
-  if (Arch[0] == 'v' && std::isdigit(Arch[1]))
+  if (Arch.size() >= 2 && Arch[0] == 'v' && std::isdigit(Arch[1]))
     return (Arch[1] - 48);
   return 0;
 }
 
 // ======================================================= //
 // Parsers
 // ======================================================= //
 
StringRef llvm::ARM::getCanonicalArchName(StringRef Arch) {
 
   // Empty string means offset reached the end, which means it's valid.
   if (A.empty())
     return Arch;
 
   // Only match non-marketing names
   if (offset != StringRef::npos) {
     // Must start with 'vN'.
-    if (A[0] != 'v' || !std::isdigit(A[1]))
+    if (A.size() >= 2 && (A[0] != 'v' || !std::isdigit(A[1])))
       return Error;
     // Can't have an extra 'eb'.
     if (A.find("eb") != StringRef::npos)
       return Error;
   }
 
   // Arch will either be a 'v' name (v7a) or a marketing name (xscale).
   return A;

unittests/Support/TargetParserTest.cpp

EXPECT_TRUE(testARMCPU("iwmmxt", "iwmmxt", "none",
                          ARM::AEK_NONE, "iwmmxt"));
   EXPECT_TRUE(testARMCPU("xscale", "xscale", "none",
                          ARM::AEK_NONE, "xscale"));
   EXPECT_TRUE(testARMCPU("swift", "armv7s", "neon-vfpv4",
                          ARM::AEK_HWDIVARM | ARM::AEK_HWDIVTHUMB | ARM::AEK_DSP,
                          "7-S"));
 }
 
+TEST(TargetParserTest, testInvalidARMArch) {
+  auto InvalidArchStrings = {"armv", "armv99", "noarm"};
+  for (const char* InvalidArch : InvalidArchStrings)
+    EXPECT_EQ(ARM::parseArch(InvalidArch), ARM::ArchKind::INVALID);
+}
+
 bool testARMArch(StringRef Arch, StringRef DefaultCPU, StringRef SubArch,
                  unsigned ArchAttr) {
   ARM::ArchKind AK = ARM::parseArch(Arch);
   return (AK!= ARM::ArchKind::INVALID) &
          ARM::getDefaultCPU(Arch).equals(DefaultCPU) &
          ARM::getSubArch(AK).equals(SubArch) &
          (ARM::getArchAttr(AK) == ArchAttr);
 }