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For a 256-bit BUILD_VECTOR consisting mostly of shuffles of 256-bit vectors,
both the BUILD_VECTOR and its operands may need to be legalized in multiple
steps. Consider:
(v8f32 (BUILD_VECTOR (extract_vector_elt (v8f32 %vreg0,) Constant<1>),
(extract_vector_elt %vreg0, Constant<2>),
(extract_vector_elt %vreg0, Constant<3>),
(extract_vector_elt %vreg0, Constant<4>),
(extract_vector_elt %vreg0, Constant<5>),
(extract_vector_elt %vreg0, Constant<6>),
(extract_vector_elt %vreg0, Constant<7>),
%vreg1))
a. We can't build a 256-bit vector efficiently so, we need to split it into
two 128-bit vecs and combine them with VINSERTX128.
b. Operands like (extract_vector_elt (v8f32 %vreg0), Constant<7>) needs to be
split into a VEXTRACTX128 and a further extract_vector_elt from the
resulting 128-bit vector.
c. The extract_vector_elt from b. is lowered into a shuffle to the first
element and a movss.
Depending on the order in which we legalize the BUILD_VECTOR and its
operands[1], buildFromShuffleMostly may be faced with:
(v4f32 (BUILD_VECTOR (extract_vector_elt
(vector_shuffle<1,u,u,u> (extract_subvector %vreg0, Constant<4>), undef),
Constant<0>),
(extract_vector_elt
(vector_shuffle<2,u,u,u> (extract_subvector %vreg0, Constant<4>), undef),
Constant<0>),
(extract_vector_elt
(vector_shuffle<3,u,u,u> (extract_subvector %vreg0, Constant<4>), undef),
Constant<0>),
%vreg1))
In order to figure out the underlying vector and their identity we need to see
through the shuffles.
[1] Note that the order in which operations and their operands are legalized is
only guaranteed in the first iteration of LegalizeDAG.
Fixes <rdar://problem/16296956>
llvm-svn: 206634
22 lines
835 B
LLVM
22 lines
835 B
LLVM
; RUN: llc < %s -mtriple=x86_64-apple-darwin -mcpu=corei7-avx | FileCheck %s
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; Use buildFromShuffleMostly which allows this to be generated as two 128-bit
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; shuffles and an insert.
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; This is the (somewhat questionable) LLVM IR that is generated for:
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; x8.s0123456 = x8.s1234567; // x8 is a <8 x float> type
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; x8.s7 = f; // f is float
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define <8 x float> @test1(<8 x float> %a, float %b) {
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; CHECK-LABEL: test1:
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; CHECK: vinsertps
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; CHECK-NOT: vinsertps
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entry:
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%shift = shufflevector <8 x float> %a, <8 x float> undef, <7 x i32> <i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
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%extend = shufflevector <7 x float> %shift, <7 x float> undef, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 undef>
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%insert = insertelement <8 x float> %extend, float %b, i32 7
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ret <8 x float> %insert
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}
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