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[AArch64] Improve cost of vector division by constant 

With custom lowering for vector MULLH{S,U}, it is now profitable to
vectorize a divide by constant loop for the custom types (v16i8, v8i16,
and v4i32).  The cost if based on TargetLowering::Build{S,U}DIV which
uses a multiply by constant plus adjustment to express a divide by
constant.

Both {u,s}mull{2} are expressed as Instruction::Mul and shifts by
Instruction::AShr.

llvm-svn: 331873
This commit is contained in:
Adhemerval Zanella 2018-05-09 12:48:22 +00:00
parent 3934dba059
commit f384bc7166
2 changed files with 67 additions and 0 deletions
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22
llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
View File

@ -520,6 +520,28 @@ int AArch64TTIImpl::getArithmeticInstrCost(
}
LLVM_FALLTHROUGH;
case ISD::UDIV:
if (Opd2Info == TargetTransformInfo::OK_UniformConstantValue) {
auto VT = TLI->getValueType(DL, Ty);
if (TLI->isOperationLegalOrCustom(ISD::MULHU, VT)) {
// Vector signed division by constant are expanded to the
// sequence MULHS + ADD/SUB + SRA + SRL + ADD, and unsigned division
// to MULHS + SUB + SRL + ADD + SRL.
int MulCost = getArithmeticInstrCost(Instruction::Mul, Ty, Opd1Info,
Opd2Info,
TargetTransformInfo::OP_None,
TargetTransformInfo::OP_None);
int AddCost = getArithmeticInstrCost(Instruction::Add, Ty, Opd1Info,
Opd2Info,
TargetTransformInfo::OP_None,
TargetTransformInfo::OP_None);
int ShrCost = getArithmeticInstrCost(Instruction::AShr, Ty, Opd1Info,
Opd2Info,
TargetTransformInfo::OP_None,
TargetTransformInfo::OP_None);
return MulCost * 2 + AddCost * 2 + ShrCost * 2 + 1;
}
}
Cost += BaseT::getArithmeticInstrCost(Opcode, Ty, Opd1Info, Opd2Info,
Opd1PropInfo, Opd2PropInfo);
if (Ty->isVectorTy()) {

45
llvm/test/Analysis/CostModel/AArch64/div_cte.ll Normal file
View File

@ -0,0 +1,45 @@
; RUN: opt -cost-model -analyze -mtriple=aarch64-linux-gnu -mattr=+neon < %s | FileCheck %s
; Verify the cost of integer division by constant.
define <16 x i8> @sdiv8xi16(<16 x i8> %x) {
; CHECK-LABEL: 'Cost Model Analysis' for function 'sdiv8xi16':
; CHECK: Found an estimated cost of 9 for instruction: %div = sdiv <16 x i8> %x, <i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9>
%div = sdiv <16 x i8> %x, <i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9>
ret <16 x i8> %div
}
define <8 x i16> @sdiv16xi8(<8 x i16> %x) {
; CHECK-LABEL: 'Cost Model Analysis' for function 'sdiv16xi8':
; CHECK: Found an estimated cost of 9 for instruction: %div = sdiv <8 x i16> %x, <i16 9, i16 9, i16 9, i16 9, i16 9, i16 9, i16 9, i16 9>
%div = sdiv <8 x i16> %x, <i16 9, i16 9, i16 9, i16 9, i16 9, i16 9, i16 9, i16 9>
ret <8 x i16> %div
}
define <4 x i32> @sdiv32xi4(<4 x i32> %x) {
; CHECK-LABEL: 'Cost Model Analysis' for function 'sdiv32xi4':
; CHECK: Found an estimated cost of 9 for instruction: %div = sdiv <4 x i32> %x, <i32 9, i32 9, i32 9, i32 9>
%div = sdiv <4 x i32> %x, <i32 9, i32 9, i32 9, i32 9>
ret <4 x i32> %div
}
define <16 x i8> @udiv8xi16(<16 x i8> %x) {
; CHECK-LABEL: 'Cost Model Analysis' for function 'udiv8xi16':
; CHECK: Found an estimated cost of 9 for instruction: %div = udiv <16 x i8> %x, <i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9>
%div = udiv <16 x i8> %x, <i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9, i8 9>
ret <16 x i8> %div
}
define <8 x i16> @udiv16xi8(<8 x i16> %x) {
; CHECK-LABEL: 'Cost Model Analysis' for function 'udiv16xi8':
; CHECK: Found an estimated cost of 9 for instruction: %div = udiv <8 x i16> %x, <i16 9, i16 9, i16 9, i16 9, i16 9, i16 9, i16 9, i16 9>
%div = udiv <8 x i16> %x, <i16 9, i16 9, i16 9, i16 9, i16 9, i16 9, i16 9, i16 9>
ret <8 x i16> %div
}
define <4 x i32> @udiv32xi4(<4 x i32> %x) {
; CHECK-LABEL: Printing analysis 'Cost Model Analysis' for function 'udiv32xi4':
; CHECK: Found an estimated cost of 9 for instruction: %div = udiv <4 x i32> %x, <i32 9, i32 9, i32 9, i32 9>
%div = udiv <4 x i32> %x, <i32 9, i32 9, i32 9, i32 9>
ret <4 x i32> %div
}