llvm-mirror/add-of-carry.ll at 757022131f8d33cbcb31d2d71f3d752b50c299d0 - llvm-mirror - Git.je (Gitea)

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Owen Anderson 97a8fdc19c 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

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 ; RUN: llc < %s -march=x86 | FileCheck %s
 ; <rdar://problem/8449754>
 define i32 @add32carry(i32 %sum, i32 %x) nounwind readnone ssp {
 entry:
 ; CHECK:	sbbl	%ecx, %ecx
 ; CHECK-NOT: addl
 ; CHECK: subl	%ecx, %eax
   %add4 = add i32 %x, %sum
   %cmp = icmp ult i32 %add4, %x
   %inc = zext i1 %cmp to i32
   %z.0 = add i32 %add4, %inc
   ret i32 %z.0
 }