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An entry about comi / ucomi intrinsics.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@27445 91177308-0d34-0410-b5e6-96231b3b80d8
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Evan Cheng 2006-04-05 23:46:04 +00:00
parent 6be2c58c8c
commit 8af5ef9c64
1 changed files with 31 additions and 0 deletions
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lib/Target/X86/README.txt
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@ -673,3 +673,34 @@ of a v4sf value.
Better codegen for vector_shuffles like this { x, 0, 0, 0 } or { x, 0, x, 0}.
Perhaps use pxor / xorp* to clear a XMM register first?
//===---------------------------------------------------------------------===//
Adding to the list of cmp / test poor codegen issues:
int test(__m128 *A, __m128 *B) {
if (_mm_comige_ss(*A, *B))
return 3;
else
return 4;
}
_test:
movl 8(%esp), %eax
movaps (%eax), %xmm0
movl 4(%esp), %eax
movaps (%eax), %xmm1
comiss %xmm0, %xmm1
setae %al
movzbl %al, %ecx
movl $3, %eax
movl $4, %edx
cmpl $0, %ecx
cmove %edx, %eax
ret
Note the setae, movzbl, cmpl, cmove can be replaced with a single cmovae. There
are a number of issues. 1) We are introducing a setcc between the result of the
intrisic call and select. 2) The intrinsic is expected to produce a i32 value
so a any extend (which becomes a zero extend) is added.
We probably need some kind of target DAG combine hook to fix this.