arch/x86: add support for explicit CC register file

Convert condition code registers from being specialized
("pseudo") integer registers to using the recently
added CC register class.

Nilay Vaish also contributed to this patch.

src/cpu/o3/O3CPU.py

@@ -112,7 +112,18 @@ class DerivO3CPU(BaseCPU):
     numPhysIntRegs = Param.Unsigned(256, "Number of physical integer registers")
     numPhysFloatRegs = Param.Unsigned(256, "Number of physical floating point "
                                       "registers")
-    numPhysCCRegs = Param.Unsigned(0, "Number of physical cc registers")
+    # most ISAs don't use condition-code regs, so default is 0
+    _defaultNumPhysCCRegs = 0
+    if buildEnv['TARGET_ISA'] == 'x86':
+        # For x86, each CC reg is used to hold only a subset of the
+        # flags, so we need 4-5 times the number of CC regs as
+        # physical integer regs to be sure we don't run out.  In
+        # typical real machines, CC regs are not explicitly renamed
+        # (it's a side effect of int reg renaming), so they should
+        # never be the bottleneck here.
+        _defaultNumPhysCCRegs = Self.numPhysIntRegs * 5
+    numPhysCCRegs = Param.Unsigned(_defaultNumPhysCCRegs,
+                                   "Number of physical cc registers")
     numIQEntries = Param.Unsigned(64, "Number of instruction queue entries")
     numROBEntries = Param.Unsigned(192, "Number of reorder buffer entries")