Use the fast register allocator by default for -O0 builds.

This affects both llvm-gcc and clang.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@105372 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/Passes.cpp

@@ -61,7 +61,7 @@ FunctionPass *llvm::createRegisterAllocator(CodeGenOpt::Level OptLevel) {
   // When the 'default' allocator is requested, pick one based on OptLevel.
   switch (OptLevel) {
   case CodeGenOpt::None:
-    return createLocalRegisterAllocator();
+    return createFastRegisterAllocator();
   default:
     return createLinearScanRegisterAllocator();
   }