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[SystemZ::TTI] Return zero cost for ICmp that becomes Load And Test. 

A loaded value with multiple users compared with 0 will become a load and
test single instruction. The load is not folded in this case (multiple
users), but the compare instruction is eliminated.

This patch returns 0 cost for the icmp in these cases.

Review: Ulrich Weigand
https://reviews.llvm.org/D55111

llvm-svn: 348141
This commit is contained in:
Jonas Paulsson 2018-12-03 14:30:18 +00:00
parent a50c05872e
commit 8ae0f88b13
2 changed files with 35 additions and 0 deletions
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10
llvm/lib/Target/SystemZ/SystemZTargetTransformInfo.cpp
View File

@ -839,6 +839,16 @@ int SystemZTTIImpl::getCmpSelInstrCost(unsigned Opcode, Type *ValTy,
else { // Scalar
switch (Opcode) {
case Instruction::ICmp: {
// A loaded value compared with 0 with multiple users becomes Load and
// Test. The load is then not foldable, so return 0 cost for the ICmp.
unsigned ScalarBits = ValTy->getScalarSizeInBits();
if (I != nullptr && ScalarBits >= 32)
if (LoadInst *Ld = dyn_cast<LoadInst>(I->getOperand(0)))
if (const ConstantInt *C = dyn_cast<ConstantInt>(I->getOperand(1)))
if (!Ld->hasOneUse() && Ld->getParent() == I->getParent() &&
C->getZExtValue() == 0)
return 0;
unsigned Cost = 1;
if (ValTy->isIntegerTy() && ValTy->getScalarSizeInBits() <= 16)
Cost += (I != nullptr ? getOperandsExtensionCost(I) : 2);

25
llvm/test/Analysis/CostModel/SystemZ/load-and-test.ll Normal file
View File

@ -0,0 +1,25 @@
; RUN: opt < %s -cost-model -analyze -mtriple=systemz-unknown -mcpu=z13 | FileCheck %s
;
; Test that load and test results in 0 cost for the compare.
define i64 @fun0(i64* %Src, i64 %Arg) {
%Ld1 = load i64, i64* %Src
%Cmp = icmp eq i64 %Ld1, 0
%S = select i1 %Cmp, i64 %Arg, i64 %Ld1
ret i64 %S
; CHECK: Printing analysis 'Cost Model Analysis' for function 'fun0':
; CHECK: Cost Model: Found an estimated cost of 1 for instruction: %Ld1 = load i64, i64* %Src
; CHECK: Cost Model: Found an estimated cost of 0 for instruction: %Cmp = icmp eq i64 %Ld1, 0
; CHECK: Cost Model: Found an estimated cost of 1 for instruction: %S = select
}
define i32 @fun1(i32* %Src, i32 %Arg) {
%Ld1 = load i32, i32* %Src
%Cmp = icmp eq i32 %Ld1, 0
%S = select i1 %Cmp, i32 %Arg, i32 %Ld1
ret i32 %S
; CHECK: Printing analysis 'Cost Model Analysis' for function 'fun1':
; CHECK: Cost Model: Found an estimated cost of 1 for instruction: %Ld1 = load i32, i32* %Src
; CHECK: Cost Model: Found an estimated cost of 0 for instruction: %Cmp = icmp eq i32 %Ld1, 0
; CHECK: Cost Model: Found an estimated cost of 1 for instruction: %S = select
}