[llvm-cov] Assume repeat architectures for universal binaries

[keith]

Summary

In the case you pass multiple universal binaries to llvm-cov, assume
that if only 1 architecture is passed, it should be used for all the
passed binaries.

This makes it easier to use multiple multi-arch binaries, since it's
likely very rare that your architectures mismatch significantly if you
also have multiple binaries in a single llvm-cov invocation. If the
architecture is invalid for any of the passed binaries, it will still
fail later.

[kastiglione]

+1 – it doesn't make sense to have to repeat the same -arch flag and value N times for N binaries.

llvm/test/tools/llvm-cov/universal-binary.c

 // The coverage reader should be able to handle universal binaries
 
 // CHECK: [[@LINE+1]]| 100|int main
 int main(int argc, const char *argv[]) {}
 
 // RUN: llvm-profdata merge %S/Inputs/universal-binary.proftext -o %t.profdata
 // RUN: llvm-cov show %S/Inputs/universal-binary -instr-profile %t.profdata -path-equivalence=/tmp,%S %s -arch x86_64 | FileCheck %s
 
 // RUN: llvm-cov report %S/Inputs/universal-binary -arch x86_64 -object %S/Inputs/templateInstantiations.covmapping -arch i386 -instr-profile %t.profdata 2>&1 | FileCheck %s --check-prefix=COMBINED
+// RUN: llvm-cov report %S/Inputs/universal-binary -arch x86_64 -object %S/Inputs/templateInstantiations.covmapping -instr-profile %t.profdata 2>&1 | FileCheck %s --check-prefix=COMBINED
+// RUN: not llvm-cov report %S/Inputs/universal-binary -arch i386 -object %S/Inputs/templateInstantiations.covmapping -instr-profile %t.profdata 2>&1 | FileCheck %s --check-prefix=WRONG-ARCH
 // COMBINED: showTemplateInstantiations.cpp
 // COMBINED-NEXT: universal-binary.c
 
 // RUN: not llvm-cov show %S/Inputs/universal-binary -instr-profile %t.profdata -path-equivalence=/tmp,%S %s 2>&1 | FileCheck --check-prefix=WRONG-ARCH %s
 // RUN: not llvm-cov show %S/Inputs/universal-binary -instr-profile %t.profdata -path-equivalence=/tmp,%S %s -arch i386 2>&1 | FileCheck --check-prefix=WRONG-ARCH %s
 // WRONG-ARCH: Failed to load coverage: `-arch` specifier is invalid or missing for universal binary
 
 // RUN: not llvm-cov show %S/Inputs/universal-binary -instr-profile %t.profdata -path-equivalence=/tmp,%S %s -arch definitly_a_made_up_architecture 2>&1 | FileCheck --check-prefix=MADE-UP-ARCH %s
 // MADE-UP-ARCH: Unknown architecture: definitly_a_made_up_architecture
 
 // RUN: not llvm-cov show %S/Inputs/universal-binary -instr-profile %t.profdata -path-equivalence=/tmp,%S %s -arch=x86_64 -arch=x86_64 2>&1 | FileCheck --check-prefix=TOO-MANY-ARCH %s
 // TOO-MANY-ARCH: Number of architectures doesn't match the number of objects
 //
 // RUN: not llvm-cov report -instr-profile %t.profdata 2>&1 | FileCheck --check-prefix=MISSING-BINARY %s
 // MISSING-BINARY: No filenames specified!

llvm/tools/llvm-cov/CodeCoverage.cpp

auto commandLineParser = [&, this](int argc, const char **argv) -> int {
     if (!Arches.empty()) {
       for (const std::string &Arch : Arches) {
         if (Triple(Arch).getArch() == llvm::Triple::ArchType::UnknownArch) {
           error("Unknown architecture: " + Arch);
           return 1;
         }
         CoverageArches.emplace_back(Arch);
       }
+      if (CoverageArches.size() == 1)
+        CoverageArches.insert(CoverageArches.end(), ObjectFilenames.size() - 1,
+                              CoverageArches[0]);
       if (CoverageArches.size() != ObjectFilenames.size()) {
         error("Number of architectures doesn't match the number of objects");
         return 1;
       }
     }
 
     // IgnoreFilenameFilters are applied even when InputSourceFiles specified.
     for (const std::string &File : InputSourceFiles)