Add a -stress-regalloc=<N> option.

This will limit all register classes to N registers in order to stress
test register allocation.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@151379 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/RegisterClassInfo.cpp

@@ -18,12 +18,16 @@
 #include "RegisterClassInfo.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/Target/TargetMachine.h"
-
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
 
 using namespace llvm;
 
+cl::opt<unsigned> StressRA("stress-regalloc", cl::Hidden, cl::init(0),
+                           cl::value_desc("N"),
+                           cl::desc("Limit all regclasses to N registers"));
+
 RegisterClassInfo::RegisterClassInfo() : Tag(0), MF(0), TRI(0), CalleeSaved(0)
 {}
 
@@ -99,6 +103,10 @@ void RegisterClassInfo::compute(const TargetRegisterClass *RC) const {
   // CSR aliases go after the volatile registers, preserve the target's order.
   std::copy(CSRAlias.begin(), CSRAlias.end(), &RCI.Order[N]);
 
+  // Register allocator stress test.  Clip register class to N registers.
+  if (StressRA && RCI.NumRegs > StressRA)
+    RCI.NumRegs = StressRA;
+
   // Check if RC is a proper sub-class.
   if (const TargetRegisterClass *Super = TRI->getLargestLegalSuperClass(RC))
     if (Super != RC && getNumAllocatableRegs(Super) > RCI.NumRegs)