Add fast register allocator, enabled with -regalloc=fast.

So far this is just a clone of -regalloc=local that has been lobotomized to run
25% faster. It drops the least-recently-used calculations, and is just plain
stupid when it runs out of registers.

The plan is to make this go even faster for -O0 by taking advantage of the short
live intervals in unoptimized code. It should not be necessary to calculate
liveness when most virtual registers are killed 2-3 instructions after they are
born.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@102006 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/LinkAllCodegenComponents.h

@@ -34,6 +34,7 @@ namespace {
       (void) llvm::createDeadMachineInstructionElimPass();
 
       (void) llvm::createLocalRegisterAllocator();
+      (void) llvm::createFastRegisterAllocator();
       (void) llvm::createLinearScanRegisterAllocator();
       (void) llvm::createPBQPRegisterAllocator();
 

include/llvm/CodeGen/Passes.h

@@ -95,6 +95,11 @@ namespace llvm {
   ///
   FunctionPass *createLocalRegisterAllocator();
 
+  /// FastRegisterAllocation Pass - This pass register allocates as fast as
+  /// possible. It is best suited for debug code where live ranges are short.
+  ///
+  FunctionPass *createFastRegisterAllocator();
+
   /// LinearScanRegisterAllocation Pass - This pass implements the linear scan
   /// register allocation algorithm, a global register allocator.
   ///

lib/CodeGen/CMakeLists.txt

@@ -50,6 +50,7 @@ add_llvm_library(LLVMCodeGen
   ProcessImplicitDefs.cpp
   PrologEpilogInserter.cpp
   PseudoSourceValue.cpp
+  RegAllocFast.cpp
   RegAllocLinearScan.cpp
   RegAllocLocal.cpp
   RegAllocPBQP.cpp