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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@46413 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2008-01-27 07:31:41 +00:00
parent 71d07a0dac
commit f6b935d8e6
1 changed files with 39 additions and 0 deletions
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39
lib/Target/X86/README-SSE.txt
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@ -722,3 +722,42 @@ CodeGen/X86/vec_align.ll tests whether we can turn 4 scalar loads into a single
vec_align.ll without -relocation-model=static, you'll see what I mean.
//===---------------------------------------------------------------------===//
We should lower store(fneg(load p), q) into an integer load+xor+store, which
eliminates a constant pool load. For example, consider:
define i64 @ccosf(float %z.0, float %z.1) nounwind readonly {
entry:
%tmp6 = sub float -0.000000e+00, %z.1 ; <float> [#uses=1]
%tmp20 = tail call i64 @ccoshf( float %tmp6, float %z.0 ) nounwind readonly ; <i64> [#uses=1]
ret i64 %tmp20
}
This currently compiles to:
LCPI1_0: # <4 x float>
.long 2147483648 # float -0
.long 2147483648 # float -0
.long 2147483648 # float -0
.long 2147483648 # float -0
_ccosf:
subl $12, %esp
movss 16(%esp), %xmm0
movss %xmm0, 4(%esp)
movss 20(%esp), %xmm0
xorps LCPI1_0, %xmm0
movss %xmm0, (%esp)
call L_ccoshf$stub
addl $12, %esp
ret
Note the load into xmm0, then xor (to negate), then store. In PIC mode,
this code computes the pic base and does two loads to do the constant pool
load, so the improvement is much bigger.
The tricky part about this xform is that the argument load/store isn't exposed
until post-legalize, and at that point, the fneg has been custom expanded into
an X86 fxor. This means that we need to handle this case in the x86 backend
instead of in target independent code.
//===---------------------------------------------------------------------===//