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Add a random not very important note 

llvm-svn: 47704
This commit is contained in:
Chris Lattner 2008-02-28 04:52:59 +00:00
parent c799065cc3
commit 83e80cd368
1 changed files with 38 additions and 0 deletions
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38
llvm/lib/Target/X86/README.txt
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@ -1687,3 +1687,41 @@ doload64:
ret
//===---------------------------------------------------------------------===//
We compile this function:
define i32 @foo(i32 %a, i32 %b, i32 %c, i8 zeroext %d) nounwind {
entry:
%tmp2 = icmp eq i8 %d, 0 ; <i1> [#uses=1]
br i1 %tmp2, label %bb7, label %bb
bb: ; preds = %entry
%tmp6 = add i32 %b, %a ; <i32> [#uses=1]
ret i32 %tmp6
bb7: ; preds = %entry
%tmp10 = sub i32 %a, %c ; <i32> [#uses=1]
ret i32 %tmp10
}
to:
_foo:
cmpb $0, 16(%esp)
movl 12(%esp), %ecx
movl 8(%esp), %eax
movl 4(%esp), %edx
je LBB1_2 # bb7
LBB1_1: # bb
addl %edx, %eax
ret
LBB1_2: # bb7
movl %edx, %eax
subl %ecx, %eax
ret
The coallescer could coallesce "edx" with "eax" to avoid the movl in LBB1_2
if it commuted the addl in LBB1_1.
//===---------------------------------------------------------------------===//