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fd39c19164
Pass MemCpyOpt doesn't check if a store instruction is nontemporal.
As a consequence, adjacent nontemporal stores are always merged into a
memset call.
Example:
;;;
define void @foo(<4 x float>* nocapture %p) {
entry:
store <4 x float> zeroinitializer, <4 x float>* %p, align 16, !nontemporal !0
%p1 = getelementptr inbounds <4 x float>, <4 x float>* %dst, i64 1
store <4 x float> zeroinitializer, <4 x float>* %p1, align 16, !nontemporal !0
ret void
}
!0 = !{i32 1}
;;;
In this example, the two nontemporal stores are combined to a memset of zero
which does not preserve the nontemporal hint. Later on the backend (tested on a
x86-64 corei7) expands that memset call into a sequence of two normal 16-byte
aligned vector stores.
opt -memcpyopt example.ll -S -o - | llc -mcpu=corei7 -o -
Before:
xorps %xmm0, %xmm0
movaps %xmm0, 16(%rdi)
movaps %xmm0, (%rdi)
With this patch, we no longer merge nontemporal stores into calls to memset.
In this example, llc correctly expands the two stores into two movntps:
xorps %xmm0, %xmm0
movntps %xmm0, 16(%rdi)
movntps %xmm0, (%rdi)
In theory, we could extend the usage of !nontemporal metadata to memcpy/memset
calls. However a change like that would only have the effect of forcing the
backend to expand !nontemporal memsets back to sequences of store instructions.
A memset library call would not have exactly the same semantic of a builtin
!nontemporal memset call. So, SelectionDAG will have to conservatively expand
it back to a sequence of !nontemporal stores (effectively undoing the merging).
Differential Revision: http://reviews.llvm.org/D13519
llvm-svn: 249820
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|---|---|---|
| .. | ||
| 2008-02-24-MultipleUseofSRet.ll | ||
| 2008-03-13-ReturnSlotBitcast.ll | ||
| 2011-06-02-CallSlotOverwritten.ll | ||
| align.ll | ||
| atomic.ll | ||
| callslot_aa.ll | ||
| callslot_deref.ll | ||
| capturing-func.ll | ||
| crash.ll | ||
| form-memset.ll | ||
| loadstore-sret.ll | ||
| memcpy-to-memset-with-lifetimes.ll | ||
| memcpy-to-memset.ll | ||
| memcpy-undef.ll | ||
| memcpy.ll | ||
| memmove.ll | ||
| memset-memcpy-redundant-memset.ll | ||
| memset-memcpy-to-2x-memset.ll | ||
| nontemporal.ll | ||
| smaller.ll | ||
| sret.ll | ||