[mips] Fix more incorrect uses of HasMips64 and isMips64()

Summary:
- Conditional moves acting on 64-bit GPR's should require MIPS-IV rather than MIPS64
- ISD::MUL, and ISD::MULH[US] should be lowered on all 64-bit ISA's

Patch by David Chisnall
His work was sponsored by: DARPA, AFRL

I've added additional testcases to cover as much of the codegen changes
affecting MIPS-IV as I can. Where I've been unable to find an existing
MIPS64 testcase that can be re-used for MIPS-IV (mainly tests covering
ISD::GlobalAddress and similar), I at least agree that MIPS-IV should
behave like MIPS64. Further testcases that are fixed by this patch will follow
in my next commit. The testcases from that commit that fail for MIPS-IV without
this patch are:
    LLVM :: CodeGen/Mips/2010-07-20-Switch.ll
    LLVM :: CodeGen/Mips/cmov.ll
    LLVM :: CodeGen/Mips/eh-dwarf-cfa.ll
    LLVM :: CodeGen/Mips/largeimmprinting.ll
    LLVM :: CodeGen/Mips/longbranch.ll
    LLVM :: CodeGen/Mips/mips64-f128.ll
    LLVM :: CodeGen/Mips/mips64directive.ll
    LLVM :: CodeGen/Mips/mips64ext.ll
    LLVM :: CodeGen/Mips/mips64fpldst.ll
    LLVM :: CodeGen/Mips/mips64intldst.ll
    LLVM :: CodeGen/Mips/mips64load-store-left-right.ll
    LLVM :: CodeGen/Mips/sint-fp-store_pattern.ll

Reviewers: dsanders

Reviewed By: dsanders

CC: matheusalmeida

Differential Revision: http://reviews.llvm.org/D3343

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206183 91177308-0d34-0410-b5e6-96231b3b80d8

test/CodeGen/Mips/cmov.ll

@@ -1,6 +1,7 @@
 ; RUN: llc -march=mips < %s | FileCheck %s -check-prefix=O32
 ; RUN: llc -march=mips -regalloc=basic < %s | FileCheck %s -check-prefix=O32
 ; RUN: llc -march=mips64el -mcpu=mips64 -mattr=n64 < %s | FileCheck %s -check-prefix=N64
+; RUN: llc -march=mips64el -mcpu=mips4 -mattr=n64 < %s | FileCheck %s -check-prefix=N64
 
 @i1 = global [3 x i32] [i32 1, i32 2, i32 3], align 4
 @i3 = common global i32* null, align 4
@@ -238,4 +239,4 @@ define i32 @slti6(i32 %a) nounwind readnone {
 ; O32-DAG: xori [[R1]], [[R1]], 1
 ; O32-DAG: addiu [[R2:\$[0-9]+]], [[R1]], 3
 ; O32-NOT: movn
-; O32:.size slti6
+; O32:.size slti6