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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
50 lines
2.7 KiB
LLVM
50 lines
2.7 KiB
LLVM
; RUN: opt < %s -memcpyopt -S | FileCheck %s
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target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
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; Verify that we don't combine nontemporal stores into memset calls.
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define void @nontemporal_stores_1(<4 x float>* nocapture %dst) {
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; CHECK-LABEL: @nontemporal_stores_1
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; CHECK: store <4 x float> zeroinitializer, <4 x float>* %dst, align 16, !nontemporal !0
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; CHECK: store <4 x float> zeroinitializer, <4 x float>* %ptr1, align 16, !nontemporal !0
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; CHECK: store <4 x float> zeroinitializer, <4 x float>* %ptr2, align 16, !nontemporal !0
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; CHECK: store <4 x float> zeroinitializer, <4 x float>* %ptr3, align 16, !nontemporal !0
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; CHECK: store <4 x float> zeroinitializer, <4 x float>* %ptr4, align 16, !nontemporal !0
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; CHECK: store <4 x float> zeroinitializer, <4 x float>* %ptr5, align 16, !nontemporal !0
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; CHECK: store <4 x float> zeroinitializer, <4 x float>* %ptr6, align 16, !nontemporal !0
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; CHECK: store <4 x float> zeroinitializer, <4 x float>* %ptr7, align 16, !nontemporal !0
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; CHECK-NEXT: ret void
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entry:
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store <4 x float> zeroinitializer, <4 x float>* %dst, align 16, !nontemporal !0
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%ptr1 = getelementptr inbounds <4 x float>, <4 x float>* %dst, i64 1
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store <4 x float> zeroinitializer, <4 x float>* %ptr1, align 16, !nontemporal !0
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%ptr2 = getelementptr inbounds <4 x float>, <4 x float>* %dst, i64 2
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store <4 x float> zeroinitializer, <4 x float>* %ptr2, align 16, !nontemporal !0
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%ptr3 = getelementptr inbounds <4 x float>, <4 x float>* %dst, i64 3
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store <4 x float> zeroinitializer, <4 x float>* %ptr3, align 16, !nontemporal !0
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%ptr4 = getelementptr inbounds <4 x float>, <4 x float>* %dst, i64 4
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store <4 x float> zeroinitializer, <4 x float>* %ptr4, align 16, !nontemporal !0
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%ptr5 = getelementptr inbounds <4 x float>, <4 x float>* %dst, i64 5
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store <4 x float> zeroinitializer, <4 x float>* %ptr5, align 16, !nontemporal !0
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%ptr6 = getelementptr inbounds <4 x float>, <4 x float>* %dst, i64 6
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store <4 x float> zeroinitializer, <4 x float>* %ptr6, align 16, !nontemporal !0
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%ptr7 = getelementptr inbounds <4 x float>, <4 x float>* %dst, i64 7
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store <4 x float> zeroinitializer, <4 x float>* %ptr7, align 16, !nontemporal !0
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ret void
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}
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define void @nontemporal_stores_2(<4 x float>* nocapture %dst) {
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; CHECK-LABEL: @nontemporal_stores_2
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; CHECK: store <4 x float> zeroinitializer, <4 x float>* %dst, align 16, !nontemporal !0
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; CHECK: store <4 x float> zeroinitializer, <4 x float>* %ptr1, align 16, !nontemporal !0
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; CHECK-NEXT: ret void
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entry:
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store <4 x float> zeroinitializer, <4 x float>* %dst, align 16, !nontemporal !0
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%ptr1 = getelementptr inbounds <4 x float>, <4 x float>* %dst, i64 1
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store <4 x float> zeroinitializer, <4 x float>* %ptr1, align 16, !nontemporal !0
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ret void
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}
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!0 = !{i32 1}
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