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add a note for something evan noticed 

llvm-svn: 26539
This commit is contained in:
Chris Lattner 2006-03-05 01:15:18 +00:00
parent 6bc98653c2
commit c2dd7aae71
1 changed files with 28 additions and 0 deletions
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28
llvm/lib/Target/X86/README.txt
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@ -538,3 +538,31 @@ Currently the load folding imull has a higher complexity than the LEA32 pattern.
Lower memcpy / memset to a series of SSE 128 bit move instructions when it's
feasible.
//===---------------------------------------------------------------------===//
Teach the coallescer to commute 2-addr instructions, allowing us to eliminate
the reg-reg copy in this example:
float foo(int *x, float *y, unsigned c) {
float res = 0.0;
unsigned i;
for (i = 0; i < c; i++) {
float xx = (float)x[i];
xx = xx * y[i];
xx += res;
res = xx;
}
return res;
}
LBB_foo_3: # no_exit
cvtsi2ss %XMM0, DWORD PTR [%EDX + 4*%ESI]
mulss %XMM0, DWORD PTR [%EAX + 4*%ESI]
addss %XMM0, %XMM1
inc %ESI
cmp %ESI, %ECX
**** movaps %XMM1, %XMM0
jb LBB_foo_3 # no_exit
//===---------------------------------------------------------------------===//