Subzero: Make -reg-use and -reg-exclude specific to register class.

The main feature here is that when listing a register via the -reg-use or -reg-exclude option, we can limit the effect to a single register class, instead of applying it across all register classes.  Example:

  pnacl-sz -reg-use i32:eax,i32:ecx,i32:edx -reg-exclude f32:xmm0

Note that without the register class prefix, behavior is the same as before, specifically that the restriction applies to all register classes.

This requires a few high-level changes:

1. We need a mechanism to name *all* register classes, not just the standard ones that map to IceType values.

2. While we're at it, give standard types a more usable name, e.g. "v4i32" instead of "<4 x i32>".

3. Since we've commandeered ":" as the class/register token separator, we change ARM i64 register pair names from e.g. "r0:r1" to "r0r1".

The motivation is that for register allocator torture testing, we'd like to drastically restrict the registers available to e.g. the extensively-used i32 register class, while not overly restricting the seldom-used i32to8 register class (which reflects the set of i32 registers that may trivially truncate to i8).

BUG= none
R=kschimpf@google.com

Review URL: https://codereview.chromium.org/1614273002 .
diff --git a/src/IceTargetLoweringMIPS32.cpp b/src/IceTargetLoweringMIPS32.cpp
index 248c073..3cbf03e 100644
--- a/src/IceTargetLoweringMIPS32.cpp
+++ b/src/IceTargetLoweringMIPS32.cpp
@@ -60,6 +60,17 @@
 // The maximum number of arguments to pass in GPR registers.
 constexpr uint32_t MIPS32_MAX_GPR_ARG = 4;
 
+IceString getRegClassName(RegClass C) {
+  auto ClassNum = static_cast<RegClassMIPS32>(C);
+  assert(ClassNum < RCMIPS32_NUM);
+  switch (ClassNum) {
+  default:
+    assert(C < RC_Target);
+    return regClassString(C);
+    // Add handling of new register classes below.
+  }
+}
+
 } // end of anonymous namespace
 
 TargetMIPS32::TargetMIPS32(Cfg *Func) : TargetLowering(Func) {}
@@ -106,9 +117,8 @@
   TypeToRegisterSet[IceType_v4f32] = VectorRegisters;
 
   filterTypeToRegisterSet(Ctx, RegMIPS32::Reg_NUM, TypeToRegisterSet,
-                          RCMIPS32_NUM, [](int32_t RegNum) -> IceString {
-                            return RegMIPS32::getRegName(RegNum);
-                          });
+                          llvm::array_lengthof(TypeToRegisterSet),
+                          RegMIPS32::getRegName, getRegClassName);
 }
 
 void TargetMIPS32::translateO2() {
@@ -1115,7 +1125,7 @@
       << "nomips16\n";
 }
 
-llvm::SmallBitVector TargetMIPS32::TypeToRegisterSet[IceType_NUM];
+llvm::SmallBitVector TargetMIPS32::TypeToRegisterSet[RCMIPS32_NUM];
 llvm::SmallBitVector TargetMIPS32::RegisterAliases[RegMIPS32::Reg_NUM];
 
 } // end of namespace MIPS32