Codegen integer abs more efficiently using the trick from the PPC CWG. This

Codegen integer abs more efficiently using the trick from the PPC CWG.  This
improves codegen on many architectures.  Tests committed as CodeGen/*/iabs.ll

X86 Old:			X86 New:
_test:				_test:
   movl 4(%esp), %ecx		   movl 4(%esp), %eax
   movl %ecx, %eax		   movl %eax, %ecx
   negl %eax			   sarl $31, %ecx
   testl %ecx, %ecx		   addl %ecx, %eax
   cmovns %ecx, %eax		   xorl %ecx, %eax
   ret				   ret

PPC Old:			PPC New:
_test:				_test:
   cmpwi cr0, r3, -1		   srawi r2, r3, 31
   neg r2, r3			   add r3, r3, r2
   bgt cr0, LBB1_2 ;		   xor r3, r3, r2
LBB1_1: ;			   blr
   mr r3, r2
LBB1_2: ;
   blr

ARM Old:			ARM New:
_test:				_test:
   rsb r3, r0, #0		   add r3, r0, r0, asr #31
   cmp r0, #0			   eor r0, r3, r0, asr #31
   movge r3, r0			   bx lr
   mov r0, r3
   bx lr

Thumb Old:			Thumb New:
_test:				_test:
   neg r2, r0			   asr r2, r0, #31
   cmp r0, #0			   add r0, r0, r2
   bge LBB1_2			   eor r0, r2
LBB1_1: @			   bx lr
   cpy r0, r2
LBB1_2: @
   bx lr

Sparc Old:			Sparc New:
test:				test:
   save -96, %o6, %o6		   save -96, %o6, %o6
   sethi 0, %l0			   sra %i0, 31, %l0
   sub %l0, %i0, %l0		   add %i0, %l0, %l1
   subcc %i0, -1, %l1		   xor %l1, %l0, %i0
   bg .BB1_2			   restore %g0, %g0, %g0
   nop				   retl
.BB1_1:				   nop
   or %g0, %l0, %i0
.BB1_2:
   restore %g0, %g0, %g0
   retl
   nop

It also helps alpha/ia64 :)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@35881 91177308-0d34-0410-b5e6-96231b3b80d8