[PATCH] Forbid the use of registers t6, t7 and t8 if the target is MIPS NaCl.

[Mark Seaborn]

  LGTM


================
Comment at: lib/Target/Mips/MipsCallingConv.td:198
@@ +197,3 @@
+
+  // In NaCl, T6, T7 and T8 are reserved and not available as argument
+  // registers for fastcc.
----------------
Can you also address Eric's earlier comment, that it would be good to also say here, briefly, what the registers are reserved for?

================
Comment at: lib/Target/Mips/MipsRegisterInfo.cpp:137
@@ -136,1 +136,3 @@
 
+  // Reserved for NaCl use.
+  if (Subtarget.isTargetNaCl()) {
----------------
Eric's earlier comment was that comments should be complete sentences.  Maybe "These registers are reserved by the NaCl sandbox"?

================
Comment at: test/CodeGen/Mips/nacl-reserved-regs.ll:8
@@ +7,3 @@
+define void @f() {
+entry:
+  %val1 = load volatile i32* @var
----------------
FWIW, you don't need to name the entry block


http://llvm-reviews.chandlerc.com/D2694