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Revert "[InstCombine] canonicalize trunc + insert as bitcast + shuffl…
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…e, part 2"

This reverts commit dd8d0d2.
As discussed in the planned follow-on to this patch (D138874),
this and the previous patch in this set can cause trouble for
the backend, and there's probably no quick fix. We may even
want to canonicalize in the opposite direction (towards insertelt).
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@rotateright
rotateright committed Dec 8, 2022
1 parent ea6ed39 commit 286ae63
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Showing 2 changed files with 33 additions and 65 deletions.
13 changes: 2 additions & 11 deletions llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
View file
Expand Up @@ -1545,17 +1545,8 @@ static Instruction *foldTruncInsElt(InsertElementInst &InsElt, bool IsBigEndian,
// The insert is to the LSB end of the vector (depends on endian).
// That's all we need.
} else {
// If not, we must match a right-shift to translate the insert index.
uint64_t ShiftC;
if (!match(T, m_OneUse(m_LShr(m_Value(X), m_ConstantInt(ShiftC)))))
return nullptr;

// Check the shift amount to see if this can be folded to an identity
// shuffle (assuming we are shuffling with an undef base vector).
// Big endian has MSB at vector index 0, so the insert index is flipped.
if (ShiftC != (IsBigEndian ? (NumEltsInScalar - 1 - IndexC) * VecEltWidth
: IndexC * VecEltWidth))
return nullptr;
// TODO: Look through a shift-right and translate the insert index.
return nullptr;
}

// Bitcast the scalar to a vector type with the destination element type.
Expand Down
85 changes: 31 additions & 54 deletions llvm/test/Transforms/InstCombine/insert-trunc.ll
View file
Expand Up @@ -143,16 +143,11 @@ define <4 x i8> @low_index_shorter_length_poison_basevec_extra_use(i64 %x) {
}

define <4 x i16> @lshr_same_length_poison_basevec_le(i64 %x) {
; BE-LABEL: @lshr_same_length_poison_basevec_le(
; BE-NEXT: [[S:%.*]] = lshr i64 [[X:%.*]], 32
; BE-NEXT: [[T:%.*]] = trunc i64 [[S]] to i16
; BE-NEXT: [[R:%.*]] = insertelement <4 x i16> poison, i16 [[T]], i64 2
; BE-NEXT: ret <4 x i16> [[R]]
;
; LE-LABEL: @lshr_same_length_poison_basevec_le(
; LE-NEXT: [[VEC_X:%.*]] = bitcast i64 [[X:%.*]] to <4 x i16>
; LE-NEXT: [[R:%.*]] = shufflevector <4 x i16> [[VEC_X]], <4 x i16> poison, <4 x i32> <i32 undef, i32 undef, i32 2, i32 undef>
; LE-NEXT: ret <4 x i16> [[R]]
; ALL-LABEL: @lshr_same_length_poison_basevec_le(
; ALL-NEXT: [[S:%.*]] = lshr i64 [[X:%.*]], 32
; ALL-NEXT: [[T:%.*]] = trunc i64 [[S]] to i16
; ALL-NEXT: [[R:%.*]] = insertelement <4 x i16> poison, i16 [[T]], i64 2
; ALL-NEXT: ret <4 x i16> [[R]]
;
%s = lshr i64 %x, 32
%t = trunc i64 %s to i16
Expand All @@ -161,16 +156,11 @@ define <4 x i16> @lshr_same_length_poison_basevec_le(i64 %x) {
}

define <4 x i16> @lshr_same_length_poison_basevec_be(i64 %x) {
; BE-LABEL: @lshr_same_length_poison_basevec_be(
; BE-NEXT: [[VEC_X:%.*]] = bitcast i64 [[X:%.*]] to <4 x i16>
; BE-NEXT: [[R:%.*]] = shufflevector <4 x i16> [[VEC_X]], <4 x i16> poison, <4 x i32> <i32 undef, i32 1, i32 undef, i32 undef>
; BE-NEXT: ret <4 x i16> [[R]]
;
; LE-LABEL: @lshr_same_length_poison_basevec_be(
; LE-NEXT: [[S:%.*]] = lshr i64 [[X:%.*]], 32
; LE-NEXT: [[T:%.*]] = trunc i64 [[S]] to i16
; LE-NEXT: [[R:%.*]] = insertelement <4 x i16> poison, i16 [[T]], i64 1
; LE-NEXT: ret <4 x i16> [[R]]
; ALL-LABEL: @lshr_same_length_poison_basevec_be(
; ALL-NEXT: [[S:%.*]] = lshr i64 [[X:%.*]], 32
; ALL-NEXT: [[T:%.*]] = trunc i64 [[S]] to i16
; ALL-NEXT: [[R:%.*]] = insertelement <4 x i16> poison, i16 [[T]], i64 1
; ALL-NEXT: ret <4 x i16> [[R]]
;
%s = lshr i64 %x, 32
%t = trunc i64 %s to i16
Expand All @@ -180,8 +170,9 @@ define <4 x i16> @lshr_same_length_poison_basevec_be(i64 %x) {

define <4 x i16> @lshr_same_length_poison_basevec_both_endian(i64 %x) {
; BE-LABEL: @lshr_same_length_poison_basevec_both_endian(
; BE-NEXT: [[VEC_X:%.*]] = bitcast i64 [[X:%.*]] to <4 x i16>
; BE-NEXT: [[R:%.*]] = shufflevector <4 x i16> [[VEC_X]], <4 x i16> poison, <4 x i32> <i32 0, i32 undef, i32 undef, i32 undef>
; BE-NEXT: [[S:%.*]] = lshr i64 [[X:%.*]], 48
; BE-NEXT: [[T:%.*]] = trunc i64 [[S]] to i16
; BE-NEXT: [[R:%.*]] = insertelement <4 x i16> poison, i16 [[T]], i64 0
; BE-NEXT: ret <4 x i16> [[R]]
;
; LE-LABEL: @lshr_same_length_poison_basevec_both_endian(
Expand Down Expand Up @@ -217,8 +208,9 @@ define <8 x i16> @lshr_longer_length_poison_basevec_le(i64 %x) {
; BE-NEXT: ret <8 x i16> [[R]]
;
; LE-LABEL: @lshr_longer_length_poison_basevec_le(
; LE-NEXT: [[VEC_X:%.*]] = bitcast i64 [[X:%.*]] to <4 x i16>
; LE-NEXT: [[R:%.*]] = shufflevector <4 x i16> [[VEC_X]], <4 x i16> poison, <8 x i32> <i32 undef, i32 undef, i32 undef, i32 3, i32 undef, i32 undef, i32 undef, i32 undef>
; LE-NEXT: [[S:%.*]] = lshr i64 [[X:%.*]], 48
; LE-NEXT: [[T:%.*]] = trunc i64 [[S]] to i16
; LE-NEXT: [[R:%.*]] = insertelement <8 x i16> poison, i16 [[T]], i64 3
; LE-NEXT: ret <8 x i16> [[R]]
;
%s = lshr i64 %x, 48
Expand All @@ -228,16 +220,11 @@ define <8 x i16> @lshr_longer_length_poison_basevec_le(i64 %x) {
}

define <8 x i16> @lshr_longer_length_poison_basevec_be(i64 %x) {
; BE-LABEL: @lshr_longer_length_poison_basevec_be(
; BE-NEXT: [[VEC_X:%.*]] = bitcast i64 [[X:%.*]] to <4 x i16>
; BE-NEXT: [[R:%.*]] = shufflevector <4 x i16> [[VEC_X]], <4 x i16> poison, <8 x i32> <i32 undef, i32 1, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef>
; BE-NEXT: ret <8 x i16> [[R]]
;
; LE-LABEL: @lshr_longer_length_poison_basevec_be(
; LE-NEXT: [[S:%.*]] = lshr i64 [[X:%.*]], 32
; LE-NEXT: [[T:%.*]] = trunc i64 [[S]] to i16
; LE-NEXT: [[R:%.*]] = insertelement <8 x i16> poison, i16 [[T]], i64 1
; LE-NEXT: ret <8 x i16> [[R]]
; ALL-LABEL: @lshr_longer_length_poison_basevec_be(
; ALL-NEXT: [[S:%.*]] = lshr i64 [[X:%.*]], 32
; ALL-NEXT: [[T:%.*]] = trunc i64 [[S]] to i16
; ALL-NEXT: [[R:%.*]] = insertelement <8 x i16> poison, i16 [[T]], i64 1
; ALL-NEXT: ret <8 x i16> [[R]]
;
%s = lshr i64 %x, 32
%t = trunc i64 %s to i16
Expand All @@ -259,16 +246,11 @@ define <8 x i16> @lshr_wrong_index_longer_length_poison_basevec(i64 %x) {
}

define <2 x i16> @lshr_shorter_length_poison_basevec_le(i64 %x) {
; BE-LABEL: @lshr_shorter_length_poison_basevec_le(
; BE-NEXT: [[S:%.*]] = lshr i64 [[X:%.*]], 16
; BE-NEXT: [[T:%.*]] = trunc i64 [[S]] to i16
; BE-NEXT: [[R:%.*]] = insertelement <2 x i16> poison, i16 [[T]], i64 1
; BE-NEXT: ret <2 x i16> [[R]]
;
; LE-LABEL: @lshr_shorter_length_poison_basevec_le(
; LE-NEXT: [[VEC_X:%.*]] = bitcast i64 [[X:%.*]] to <4 x i16>
; LE-NEXT: [[R:%.*]] = shufflevector <4 x i16> [[VEC_X]], <4 x i16> poison, <2 x i32> <i32 undef, i32 1>
; LE-NEXT: ret <2 x i16> [[R]]
; ALL-LABEL: @lshr_shorter_length_poison_basevec_le(
; ALL-NEXT: [[S:%.*]] = lshr i64 [[X:%.*]], 16
; ALL-NEXT: [[T:%.*]] = trunc i64 [[S]] to i16
; ALL-NEXT: [[R:%.*]] = insertelement <2 x i16> poison, i16 [[T]], i64 1
; ALL-NEXT: ret <2 x i16> [[R]]
;
%s = lshr i64 %x, 16
%t = trunc i64 %s to i16
Expand All @@ -277,16 +259,11 @@ define <2 x i16> @lshr_shorter_length_poison_basevec_le(i64 %x) {
}

define <4 x i8> @lshr_shorter_length_poison_basevec_be(i64 %x) {
; BE-LABEL: @lshr_shorter_length_poison_basevec_be(
; BE-NEXT: [[VEC_X:%.*]] = bitcast i64 [[X:%.*]] to <8 x i8>
; BE-NEXT: [[R:%.*]] = shufflevector <8 x i8> [[VEC_X]], <8 x i8> poison, <4 x i32> <i32 undef, i32 undef, i32 2, i32 undef>
; BE-NEXT: ret <4 x i8> [[R]]
;
; LE-LABEL: @lshr_shorter_length_poison_basevec_be(
; LE-NEXT: [[S:%.*]] = lshr i64 [[X:%.*]], 40
; LE-NEXT: [[T:%.*]] = trunc i64 [[S]] to i8
; LE-NEXT: [[R:%.*]] = insertelement <4 x i8> poison, i8 [[T]], i64 2
; LE-NEXT: ret <4 x i8> [[R]]
; ALL-LABEL: @lshr_shorter_length_poison_basevec_be(
; ALL-NEXT: [[S:%.*]] = lshr i64 [[X:%.*]], 40
; ALL-NEXT: [[T:%.*]] = trunc i64 [[S]] to i8
; ALL-NEXT: [[R:%.*]] = insertelement <4 x i8> poison, i8 [[T]], i64 2
; ALL-NEXT: ret <4 x i8> [[R]]
;
%s = lshr i64 %x, 40
%t = trunc i64 %s to i8
Expand Down

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