[llvm-cov] Warn when -arch spec is missing/invalid for universal binary

llvm-cov reports a poor error message when the -arch specifier is
missing or invalid, and a binary has multiple slices. Make the error
message more specific.

rdar://40312677

1 files changed, 16 insertions, 0 deletions

diff --git a/llvm/lib/ProfileData/Coverage/CoverageMappingReader.cpp b/llvm/lib/ProfileData/Coverage/CoverageMappingReader.cpp
index b75738b..c110ab7 100644
--- a/llvm/lib/ProfileData/Coverage/CoverageMappingReader.cpp
+++ b/llvm/lib/ProfileData/Coverage/CoverageMappingReader.cpp
@@ -950,6 +950,18 @@ loadBinaryFormat(std::unique_ptr<Binary> Bin, StringRef Arch) {
       BytesInAddress, Endian);
 }
 
+/// Determine whether \p Arch is invalid or empty, given \p Bin.
+static bool isArchSpecifierInvalidOrMissing(Binary *Bin, StringRef Arch) {
+  // If we have a universal binary and Arch doesn't identify any of its slices,
+  // it's user error.
+  if (auto *Universal = dyn_cast<MachOUniversalBinary>(Bin))
+    return none_of(Universal->objects(),
+                   [Arch](const MachOUniversalBinary::ObjectForArch &Obj) {
+                     return Obj.getArchFlagName() == Arch;
+                   });
+  return false;
+}
+
 Expected<std::vector<std::unique_ptr<BinaryCoverageReader>>>
 BinaryCoverageReader::create(
     MemoryBufferRef ObjectBuffer, StringRef Arch,
@@ -970,6 +982,10 @@ BinaryCoverageReader::create(
     return BinOrErr.takeError();
   std::unique_ptr<Binary> Bin = std::move(BinOrErr.get());
 
+  if (isArchSpecifierInvalidOrMissing(Bin.get(), Arch))
+    return make_error<CoverageMapError>(
+        coveragemap_error::invalid_or_missing_arch_specifier);
+
   // MachO universal binaries which contain archives need to be treated as
   // archives, not as regular binaries.
   if (auto *Universal = dyn_cast<MachOUniversalBinary>(Bin.get())) {