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[AArch64] Improve cost computations for odd vector mem ops. (llvm#78181)
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Improve cost computaton for odd vector mem ops by breaking them down
into smaller power-of-2 parts and sum up the cost of those parts.

This fixes the current cost estimates, which for most parts
underestimated the cos, due to using getTypeLegalizationCost, which
widens to the next power-of-2 in a single step in most cases. This
doesn't reflect the actual cost.

See https://llvm.godbolt.org/z/vMsnxMf1v for codegen for the tests.

Note that there is a special case for v3i8, for which current codegen is
pretty bad, due to automatic widening to v4i8, which in turn requires
the conversion to go through memory ops in the stack. I am planning on
fixing that as a follow-up, but I am not yet sure where to best fix
this.

At the moment, there are almost no cases in which such vector operations
will be generated automatically. The motivating case is non-power-of-2
SLP vectorization: llvm#77790

PR: llvm#78181
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@fhahn @ampandey-1995
fhahn authored and ampandey-1995 committed Jan 19, 2024
1 parent 75a25c1 commit 24cd0d9
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Showing 2 changed files with 73 additions and 40 deletions.
49 changes: 41 additions & 8 deletions llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -3176,14 +3176,47 @@ InstructionCost AArch64TTIImpl::getMemoryOpCost(unsigned Opcode, Type *Ty,
if (Ty->isPtrOrPtrVectorTy())
return LT.first;

// Check truncating stores and extending loads.
if (useNeonVector(Ty) &&
Ty->getScalarSizeInBits() != LT.second.getScalarSizeInBits()) {
// v4i8 types are lowered to scalar a load/store and sshll/xtn.
if (VT == MVT::v4i8)
return 2;
// Otherwise we need to scalarize.
return cast<FixedVectorType>(Ty)->getNumElements() * 2;
if (useNeonVector(Ty)) {
// Check truncating stores and extending loads.
if (Ty->getScalarSizeInBits() != LT.second.getScalarSizeInBits()) {
// v4i8 types are lowered to scalar a load/store and sshll/xtn.
if (VT == MVT::v4i8)
return 2;
// Otherwise we need to scalarize.
return cast<FixedVectorType>(Ty)->getNumElements() * 2;
}
EVT EltVT = VT.getVectorElementType();
unsigned EltSize = EltVT.getScalarSizeInBits();
if (!isPowerOf2_32(EltSize) || EltSize < 8 || EltSize > 64 ||
VT.getVectorNumElements() >= (128 / EltSize) || !Alignment ||
*Alignment != Align(1))
return LT.first;
// FIXME: v3i8 lowering currently is very inefficient, due to automatic
// widening to v4i8, which produces suboptimal results.
if (VT.getVectorNumElements() == 3 && EltVT == MVT::i8)
return LT.first;

// Check non-power-of-2 loads/stores for legal vector element types with
// NEON. Non-power-of-2 memory ops will get broken down to a set of
// operations on smaller power-of-2 ops, including ld1/st1.
LLVMContext &C = Ty->getContext();
InstructionCost Cost(0);
SmallVector<EVT> TypeWorklist;
TypeWorklist.push_back(VT);
while (!TypeWorklist.empty()) {
EVT CurrVT = TypeWorklist.pop_back_val();
unsigned CurrNumElements = CurrVT.getVectorNumElements();
if (isPowerOf2_32(CurrNumElements)) {
Cost += 1;
continue;
}

unsigned PrevPow2 = NextPowerOf2(CurrNumElements) / 2;
TypeWorklist.push_back(EVT::getVectorVT(C, EltVT, PrevPow2));
TypeWorklist.push_back(
EVT::getVectorVT(C, EltVT, CurrNumElements - PrevPow2));
}
return Cost;
}

return LT.first;
Expand Down
64 changes: 32 additions & 32 deletions llvm/test/Analysis/CostModel/AArch64/vec3-ops.ll
View file
Original file line number Diff line number Diff line change
Expand Up @@ -3,12 +3,12 @@

define void @vec3_i32(<3 x i32> %a, <3 x i32> %b, ptr %src, ptr %dst) {
; CHECK-LABEL: 'vec3_i32'
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %l = load <3 x i32>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 2 for instruction: %l = load <3 x i32>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %add = add <3 x i32> %l, %b
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %cmp = icmp uge <3 x i32> %add, %a
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %sub = sub <3 x i32> %add, %a
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %sel = select <3 x i1> %cmp, <3 x i32> %add, <3 x i32> %sub
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: store <3 x i32> %sel, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 2 for instruction: store <3 x i32> %sel, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 0 for instruction: ret void
;
%l = load <3 x i32>, ptr %src, align 1
Expand Down Expand Up @@ -41,12 +41,12 @@ define void @vec3_i32_default_alignment(<3 x i32> %a, <3 x i32> %b, ptr %src, pt

define void @vec3_i16(<3 x i16> %a, <3 x i16> %b, ptr %src, ptr %dst) {
; CHECK-LABEL: 'vec3_i16'
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %l = load <3 x i16>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 2 for instruction: %l = load <3 x i16>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %add = add <3 x i16> %l, %b
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %cmp = icmp uge <3 x i16> %add, %a
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %sub = sub <3 x i16> %add, %a
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %sel = select <3 x i1> %cmp, <3 x i16> %add, <3 x i16> %sub
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: store <3 x i16> %sel, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 2 for instruction: store <3 x i16> %sel, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 0 for instruction: ret void
;
%l = load <3 x i16>, ptr %src, align 1
Expand All @@ -60,9 +60,9 @@ define void @vec3_i16(<3 x i16> %a, <3 x i16> %b, ptr %src, ptr %dst) {

define void @vec7_i16(ptr %src, ptr %dst) {
; CHECK-LABEL: 'vec7_i16'
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %l = load <7 x i16>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 3 for instruction: %l = load <7 x i16>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %add = add <7 x i16> %l, %l
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: store <7 x i16> %add, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 3 for instruction: store <7 x i16> %add, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 0 for instruction: ret void
;
%l = load <7 x i16>, ptr %src, align 1
Expand All @@ -73,9 +73,9 @@ define void @vec7_i16(ptr %src, ptr %dst) {

define void @vec6_i16(ptr %src, ptr %dst) {
; CHECK-LABEL: 'vec6_i16'
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %l = load <6 x i16>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 2 for instruction: %l = load <6 x i16>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %add = add <6 x i16> %l, %l
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: store <6 x i16> %add, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 2 for instruction: store <6 x i16> %add, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 0 for instruction: ret void
;
%l = load <6 x i16>, ptr %src, align 1
Expand All @@ -86,9 +86,9 @@ define void @vec6_i16(ptr %src, ptr %dst) {

define void @vec5_i16(ptr %src, ptr %dst) {
; CHECK-LABEL: 'vec5_i16'
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %l = load <5 x i16>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 2 for instruction: %l = load <5 x i16>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %add = add <5 x i16> %l, %l
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: store <5 x i16> %add, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 2 for instruction: store <5 x i16> %add, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 0 for instruction: ret void
;
%l = load <5 x i16>, ptr %src, align 1
Expand All @@ -99,12 +99,12 @@ define void @vec5_i16(ptr %src, ptr %dst) {

define void @vec3_i16_zext_i32(<3 x i32> %a, <3 x i32> %b, ptr %src, ptr %dst) {
; CHECK-LABEL: 'vec3_i16_zext_i32'
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %l = load <3 x i16>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 2 for instruction: %l = load <3 x i16>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %l.ext = zext <3 x i16> %l to <3 x i32>
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %add = add <3 x i32> %l.ext, %b
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %sub = sub <3 x i32> %add, %a
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %sub.trunc = trunc <3 x i32> %sub to <3 x i16>
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: store <3 x i16> %sub.trunc, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 2 for instruction: store <3 x i16> %sub.trunc, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 0 for instruction: ret void
;
%l = load <3 x i16>, ptr %src, align 1
Expand Down Expand Up @@ -190,10 +190,10 @@ define void @vec3_i30(<3 x i30> %a, <3 x i30> %b, ptr %src, ptr %dst) {

define void @vec3_float(<3 x float> %a, <3 x float> %b, ptr %src, ptr %dst) {
; CHECK-LABEL: 'vec3_float'
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %l = load <3 x float>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 2 for instruction: %l = load <3 x float>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %add = fadd <3 x float> %l, %b
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %sub = fsub <3 x float> %add, %a
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: store <3 x float> %sub, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 2 for instruction: store <3 x float> %sub, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 0 for instruction: ret void
;
%l = load <3 x float>, ptr %src, align 1
Expand All @@ -205,10 +205,10 @@ define void @vec3_float(<3 x float> %a, <3 x float> %b, ptr %src, ptr %dst) {

define void @vec3_half(<3 x half> %a, <3 x half> %b, ptr %src, ptr %dst) {
; CHECK-LABEL: 'vec3_half'
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %l = load <3 x half>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 2 for instruction: %l = load <3 x half>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 2 for instruction: %add = fadd <3 x half> %l, %b
; CHECK-NEXT: Cost Model: Found an estimated cost of 2 for instruction: %sub = fsub <3 x half> %add, %a
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: store <3 x half> %sub, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 2 for instruction: store <3 x half> %sub, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 0 for instruction: ret void
;
%l = load <3 x half>, ptr %src, align 1
Expand All @@ -220,9 +220,9 @@ define void @vec3_half(<3 x half> %a, <3 x half> %b, ptr %src, ptr %dst) {

define void @vec15_i8(ptr %src, ptr %dst) {
; CHECK-LABEL: 'vec15_i8'
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %l = load <15 x i8>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 4 for instruction: %l = load <15 x i8>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %add = add <15 x i8> %l, %l
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: store <15 x i8> %add, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 4 for instruction: store <15 x i8> %add, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 0 for instruction: ret void
;
%l = load <15 x i8>, ptr %src, align 1
Expand All @@ -233,9 +233,9 @@ define void @vec15_i8(ptr %src, ptr %dst) {

define void @vec14_i8(ptr %src, ptr %dst) {
; CHECK-LABEL: 'vec14_i8'
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %l = load <14 x i8>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 3 for instruction: %l = load <14 x i8>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %add = add <14 x i8> %l, %l
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: store <14 x i8> %add, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 3 for instruction: store <14 x i8> %add, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 0 for instruction: ret void
;
%l = load <14 x i8>, ptr %src, align 1
Expand All @@ -246,9 +246,9 @@ define void @vec14_i8(ptr %src, ptr %dst) {

define void @vec13_i8(ptr %src, ptr %dst) {
; CHECK-LABEL: 'vec13_i8'
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %l = load <13 x i8>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 3 for instruction: %l = load <13 x i8>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %add = add <13 x i8> %l, %l
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: store <13 x i8> %add, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 3 for instruction: store <13 x i8> %add, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 0 for instruction: ret void
;
%l = load <13 x i8>, ptr %src, align 1
Expand All @@ -259,9 +259,9 @@ define void @vec13_i8(ptr %src, ptr %dst) {

define void @vec12_i8(ptr %src, ptr %dst) {
; CHECK-LABEL: 'vec12_i8'
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %l = load <12 x i8>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 2 for instruction: %l = load <12 x i8>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %add = add <12 x i8> %l, %l
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: store <12 x i8> %add, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 2 for instruction: store <12 x i8> %add, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 0 for instruction: ret void
;
%l = load <12 x i8>, ptr %src, align 1
Expand All @@ -272,9 +272,9 @@ define void @vec12_i8(ptr %src, ptr %dst) {

define void @vec11_i8(ptr %src, ptr %dst) {
; CHECK-LABEL: 'vec11_i8'
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %l = load <11 x i8>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 3 for instruction: %l = load <11 x i8>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %add = add <11 x i8> %l, %l
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: store <11 x i8> %add, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 3 for instruction: store <11 x i8> %add, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 0 for instruction: ret void
;
%l = load <11 x i8>, ptr %src, align 1
Expand All @@ -285,10 +285,10 @@ define void @vec11_i8(ptr %src, ptr %dst) {

define void @vec7_i8(<7 x i8> %a, <7 x i8> %b, ptr %src, ptr %dst) {
; CHECK-LABEL: 'vec7_i8'
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %l = load <7 x i8>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 3 for instruction: %l = load <7 x i8>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %add = add <7 x i8> %l, %b
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %sub = sub <7 x i8> %add, %a
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: store <7 x i8> %sub, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 3 for instruction: store <7 x i8> %sub, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 0 for instruction: ret void
;
%l = load <7 x i8>, ptr %src, align 1
Expand All @@ -300,9 +300,9 @@ define void @vec7_i8(<7 x i8> %a, <7 x i8> %b, ptr %src, ptr %dst) {

define void @vec6_i8(ptr %src, ptr %dst) {
; CHECK-LABEL: 'vec6_i8'
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %l = load <6 x i8>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 2 for instruction: %l = load <6 x i8>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %add = add <6 x i8> %l, %l
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: store <6 x i8> %add, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 2 for instruction: store <6 x i8> %add, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 0 for instruction: ret void
;
%l = load <6 x i8>, ptr %src, align 1
Expand All @@ -313,9 +313,9 @@ define void @vec6_i8(ptr %src, ptr %dst) {

define void @vec5_i8(ptr %src, ptr %dst) {
; CHECK-LABEL: 'vec5_i8'
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %l = load <5 x i8>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 2 for instruction: %l = load <5 x i8>, ptr %src, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %add = add <5 x i8> %l, %l
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: store <5 x i8> %add, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 2 for instruction: store <5 x i8> %add, ptr %dst, align 1
; CHECK-NEXT: Cost Model: Found an estimated cost of 0 for instruction: ret void
;
%l = load <5 x i8>, ptr %src, align 1
Expand Down

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