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4 Commits

Author SHA1 Message Date
Shuxin Yang 01efdd6c28 (For X86) Enhancement to add-carray/sub-borrow (adc/sbb) optimization. 
The adc/sbb optimization is to able to convert following expression
into a single adc/sbb instruction:
  (ult) ... = x + 1 // where the ult is unsigned-less-than comparison
  (ult) ... = x - 1

  This change is to flip the "x >u y" (i.e. ugt comparison) in order 
to expose the adc/sbb opportunity.

llvm-svn: 167180
 2012-10-31 23:11:48 +00:00
Benjamin Kramer d724a590e5 X86: Add a bunch of peeps for add and sub of SETB. 
"b + ((a < b) ? 1 : 0)" compiles into
	cmpl	%esi, %edi
	adcl	$0, %esi
instead of
	cmpl	%esi, %edi
	sbbl	%eax, %eax
	andl	$1, %eax
	addl	%esi, %eax

This saves a register, a false dependency on %eax
(Intel's CPUs still don't ignore it) and it's shorter.

llvm-svn: 131070
 2011-05-08 18:36:07 +00:00
Chris Lattner 9edf3f50bf improve the setcc -> setcc_carry optimization to happen more 
consistently by moving it out of lowering into dag combine.

Add some missing patterns for matching away extended versions of setcc_c.

llvm-svn: 122201
 2010-12-19 22:08:31 +00:00
Owen Anderson f4b1a5bdc4 When adding the carry bit to another value on X86, exploit the fact that the carry-materialization 
(sbbl x, x) sets the registers to 0 or ~0.  Combined with two's complement arithmetic, we can fold
the intermediate AND and the ADD into a single SUB.

This fixes <rdar://problem/8449754>.

llvm-svn: 114460
 2010-09-21 18:41:19 +00:00