Avoid copies of std::strings and APInt/APFloats where we only read from it

As suggested by clang-tidy's performance-unnecessary-copy-initialization.
This can easily hit lifetime issues, so I audited every change and ran the
tests under asan, which came back clean.

llvm-svn: 272126

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/lib/Target/X86/X86MCInstLower.cpp b/llvm/lib/Target/X86/X86MCInstLower.cpp
index 00debd849cd..86bae3e08db 100644
--- a/llvm/lib/Target/X86/X86MCInstLower.cpp
+++ b/llvm/lib/Target/X86/X86MCInstLower.cpp
@@ -1543,7 +1543,7 @@ void X86AsmPrinter::EmitInstruction(const MachineInstr *MI) {
               CS << CI->getZExtValue();
             } else {
               // print multi-word constant as (w0,w1)
-              auto Val = CI->getValue();
+              const auto &Val = CI->getValue();
               CS << "(";
               for (int i = 0, N = Val.getNumWords(); i < N; ++i) {
                 if (i > 0)