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[SystemZ::TTI] Improved cost values for comparison against memory. 

Single instructions exist for i8 and i16 comparisons of memory against a
small immediate.

This patch makes sure that if the load in these cases has a single user (the
ICmp), it gets a 0 cost (folded), and also that the ICmp gets a cost of 1.

Review: Ulrich Weigand
https://reviews.llvm.org/D54897

llvm-svn: 347733
This commit is contained in:
Jonas Paulsson 2018-11-28 08:08:05 +00:00
parent 5da8e432b9
commit 011a503f25
2 changed files with 43 additions and 1 deletions
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17
llvm/lib/Target/SystemZ/SystemZTargetTransformInfo.cpp
View File

@ -835,8 +835,17 @@ int SystemZTTIImpl::getCmpSelInstrCost(unsigned Opcode, Type *ValTy,
switch (Opcode) {
case Instruction::ICmp: {
unsigned Cost = 1;
if (ValTy->isIntegerTy() && ValTy->getScalarSizeInBits() <= 16)
if (ValTy->isIntegerTy() && ValTy->getScalarSizeInBits() <= 16) {
if (I != nullptr) {
// Single instruction for comparison of memory with a small immediate.
if (const LoadInst* Ld = dyn_cast<LoadInst>(I->getOperand(0))) {
const Instruction *FoldedValue = nullptr;
if (isFoldableLoad(Ld, FoldedValue))
return Cost;
}
}
Cost += 2; // extend both operands
}
return Cost;
}
case Instruction::Select:
@ -932,6 +941,12 @@ isFoldableLoad(const LoadInst *Ld, const Instruction *&FoldedValue) {
if (SExtBits || ZExtBits)
return false;
// Comparison between memory and immediate.
if (UserI->getOpcode() == Instruction::ICmp)
if (ConstantInt *CI = dyn_cast<ConstantInt>(UserI->getOperand(1)))
if (isUInt<16>(CI->getZExtValue()))
return true;
unsigned LoadOrTruncBits = (TruncBits ? TruncBits : LoadedBits);
return (LoadOrTruncBits == 32 || LoadOrTruncBits == 64);
break;

27
llvm/test/Analysis/CostModel/SystemZ/cmp-mem.ll Normal file
View File

@ -0,0 +1,27 @@
; RUN: opt < %s -cost-model -analyze -mtriple=systemz-unknown -mcpu=z13 | FileCheck %s
;
; Test costs for i8 and i16 comparisons against memory with a small immediate.
define i32 @fun0(i8* %Src, i8* %Dst, i8 %Val) {
; CHECK: Printing analysis 'Cost Model Analysis' for function 'fun0':
; CHECK: Cost Model: Found an estimated cost of 0 for instruction: %Ld = load i8, i8* %Src
; CHECK: Cost Model: Found an estimated cost of 1 for instruction: %Cmp = icmp eq i8 %Ld, 123
; CHECK: Cost Model: Found an estimated cost of 2 for instruction: %Ret = zext i1 %Cmp to i32
; CHECK: Cost Model: Found an estimated cost of 0 for instruction: ret i32 %Ret
%Ld = load i8, i8* %Src
%Cmp = icmp eq i8 %Ld, 123
%Ret = zext i1 %Cmp to i32
ret i32 %Ret
}
define i32 @fun1(i16* %Src, i16* %Dst, i16 %Val) {
; CHECK: Printing analysis 'Cost Model Analysis' for function 'fun1':
; CHECK: Cost Model: Found an estimated cost of 0 for instruction: %Ld = load i16, i16* %Src
; CHECK: Cost Model: Found an estimated cost of 1 for instruction: %Cmp = icmp eq i16
; CHECK: Cost Model: Found an estimated cost of 2 for instruction: %Ret = zext i1 %Cmp to i32
; CHECK: Cost Model: Found an estimated cost of 0 for instruction: ret i32 %Ret
%Ld = load i16, i16* %Src
%Cmp = icmp eq i16 %Ld, 1234
%Ret = zext i1 %Cmp to i32
ret i32 %Ret
}