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//===- AMDGPUAliasAnalysis ------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
/// \file
/// This is the AMGPU address space based alias analysis pass.
//===----------------------------------------------------------------------===//
#include "AMDGPUAliasAnalysis.h"
#include "AMDGPU.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/Instructions.h"
using namespace llvm;
#define DEBUG_TYPE "amdgpu-aa"
AnalysisKey AMDGPUAA::Key;
// Register this pass...
char AMDGPUAAWrapperPass::ID = 0;
char AMDGPUExternalAAWrapper::ID = 0;
INITIALIZE_PASS(AMDGPUAAWrapperPass, "amdgpu-aa",
"AMDGPU Address space based Alias Analysis", false, true)
INITIALIZE_PASS(AMDGPUExternalAAWrapper, "amdgpu-aa-wrapper",
"AMDGPU Address space based Alias Analysis Wrapper", false, true)
ImmutablePass *llvm::createAMDGPUAAWrapperPass() {
return new AMDGPUAAWrapperPass();
}
ImmutablePass *llvm::createAMDGPUExternalAAWrapperPass() {
return new AMDGPUExternalAAWrapper();
}
AMDGPUAAWrapperPass::AMDGPUAAWrapperPass() : ImmutablePass(ID) {
initializeAMDGPUAAWrapperPassPass(*PassRegistry::getPassRegistry());
}
void AMDGPUAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesAll();
}
static AliasResult getAliasResult(unsigned AS1, unsigned AS2) {
static_assert(AMDGPUAS::MAX_AMDGPU_ADDRESS <= 7, "Addr space out of range");
if (AS1 > AMDGPUAS::MAX_AMDGPU_ADDRESS || AS2 > AMDGPUAS::MAX_AMDGPU_ADDRESS)
return AliasResult::MayAlias;
#define ASMay AliasResult::MayAlias
#define ASNo AliasResult::NoAlias
// This array is indexed by address space value enum elements 0 ... to 7
static const AliasResult ASAliasRules[8][8] = {
/* Flat Global Region Group Constant Private Const32 Buf Fat Ptr */
/* Flat */ {ASMay, ASMay, ASNo, ASMay, ASMay, ASMay, ASMay, ASMay},
/* Global */ {ASMay, ASMay, ASNo, ASNo, ASMay, ASNo, ASMay, ASMay},
/* Region */ {ASNo, ASNo, ASMay, ASNo, ASNo, ASNo, ASNo, ASNo},
/* Group */ {ASMay, ASNo, ASNo, ASMay, ASNo, ASNo, ASNo, ASNo},
/* Constant */ {ASMay, ASMay, ASNo, ASNo, ASNo, ASNo, ASMay, ASMay},
/* Private */ {ASMay, ASNo, ASNo, ASNo, ASNo, ASMay, ASNo, ASNo},
/* Constant 32-bit */ {ASMay, ASMay, ASNo, ASNo, ASMay, ASNo, ASNo, ASMay},
/* Buffer Fat Ptr */ {ASMay, ASMay, ASNo, ASNo, ASMay, ASNo, ASMay, ASMay}
};
#undef ASMay
#undef ASNo
return ASAliasRules[AS1][AS2];
}
AliasResult AMDGPUAAResult::alias(const MemoryLocation &LocA,
const MemoryLocation &LocB, AAQueryInfo &AAQI,
const Instruction *) {
unsigned asA = LocA.Ptr->getType()->getPointerAddressSpace();
unsigned asB = LocB.Ptr->getType()->getPointerAddressSpace();
AliasResult Result = getAliasResult(asA, asB);
if (Result == AliasResult::NoAlias)
return Result;
// In general, FLAT (generic) pointers could be aliased to LOCAL or PRIVATE
// pointers. However, as LOCAL or PRIVATE pointers point to local objects, in
// certain cases, it's still viable to check whether a FLAT pointer won't
// alias to a LOCAL or PRIVATE pointer.
MemoryLocation A = LocA;
MemoryLocation B = LocB;
// Canonicalize the location order to simplify the following alias check.
if (asA != AMDGPUAS::FLAT_ADDRESS) {
std::swap(asA, asB);
std::swap(A, B);
}
if (asA == AMDGPUAS::FLAT_ADDRESS &&
(asB == AMDGPUAS::LOCAL_ADDRESS || asB == AMDGPUAS::PRIVATE_ADDRESS)) {
const auto *ObjA =
getUnderlyingObject(A.Ptr->stripPointerCastsForAliasAnalysis());
if (const LoadInst *LI = dyn_cast<LoadInst>(ObjA)) {
// If a generic pointer is loaded from the constant address space, it
// could only be a GLOBAL or CONSTANT one as that address space is solely
// prepared on the host side, where only GLOBAL or CONSTANT variables are
// visible. Note that this even holds for regular functions.
if (LI->getPointerAddressSpace() == AMDGPUAS::CONSTANT_ADDRESS)
return AliasResult::NoAlias;
} else if (const Argument *Arg = dyn_cast<Argument>(ObjA)) {
const Function *F = Arg->getParent();
switch (F->getCallingConv()) {
case CallingConv::AMDGPU_KERNEL:
// In the kernel function, kernel arguments won't alias to (local)
// variables in shared or private address space.
return AliasResult::NoAlias;
default:
// TODO: In the regular function, if that local variable in the
// location B is not captured, that argument pointer won't alias to it
// as well.
break;
}
}
}
// Forward the query to the next alias analysis.
return AAResultBase::alias(LocA, LocB, AAQI, nullptr);
}
ModRefInfo AMDGPUAAResult::getModRefInfoMask(const MemoryLocation &Loc,
AAQueryInfo &AAQI,
bool IgnoreLocals) {
unsigned AS = Loc.Ptr->getType()->getPointerAddressSpace();
if (AS == AMDGPUAS::CONSTANT_ADDRESS ||
AS == AMDGPUAS::CONSTANT_ADDRESS_32BIT)
return ModRefInfo::NoModRef;
const Value *Base = getUnderlyingObject(Loc.Ptr);
AS = Base->getType()->getPointerAddressSpace();
if (AS == AMDGPUAS::CONSTANT_ADDRESS ||
AS == AMDGPUAS::CONSTANT_ADDRESS_32BIT)
return ModRefInfo::NoModRef;
return AAResultBase::getModRefInfoMask(Loc, AAQI, IgnoreLocals);
}
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