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Polish atomic pointers

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Summary:
I didn't realize that we already allowed atomic load/store of pointers,
it was added in 2012 by r162146. This patch updates the documentation
and tightens the verifier by using DataLayout to make sure that the
stored size is byte-sized and power-of-two. DataLayout is also used for
integers, and while I'm here I updated the corresponding code for
cmpxchg and rmw.

See the following discussion for context and upcoming changes to
add floating-point and vector atomics:
  https://groups.google.com/forum/#!topic/llvm-dev/Nh0P_E3CRoo/discussion

Reviewers: reames

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D15512

llvm-svn: 255931
This commit is contained in:
JF Bastien 2015-12-17 22:09:19 +00:00
parent fced76b6f1
commit 4730f05bb8
3 changed files with 46 additions and 50 deletions
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43
docs/LangRef.rst
View File

@ -6847,17 +6847,16 @@ then the optimizer is not allowed to modify the number or order of
execution of this ``load`` with other :ref:`volatile
operations <volatile>`.
If the ``load`` is marked as ``atomic``, it takes an extra
:ref:`ordering <ordering>` and optional ``singlethread`` argument. The
``release`` and ``acq_rel`` orderings are not valid on ``load``
instructions. Atomic loads produce :ref:`defined <memmodel>` results
when they may see multiple atomic stores. The type of the pointee must
be an integer or floating point type whose bit width is a power of two,
greater than or equal to eight, and less than or equal to a
target-specific size limit. ``align`` must be explicitly specified on
atomic loads, and the load has undefined behavior if the alignment is
not set to a value which is at least the size in bytes of the pointee.
``!nontemporal`` does not have any defined semantics for atomic loads.
If the ``load`` is marked as ``atomic``, it takes an extra :ref:`ordering
<ordering>` and optional ``singlethread`` argument. The ``release`` and
``acq_rel`` orderings are not valid on ``load`` instructions. Atomic loads
produce :ref:`defined <memmodel>` results when they may see multiple atomic
stores. The type of the pointee must be an integer, pointer, or floating-point
type whose bit width is a power of two greater than or equal to eight and less
than or equal to a target-specific size limit. ``align`` must be explicitly
specified on atomic loads, and the load has undefined behavior if the alignment
is not set to a value which is at least the size in bytes of the
pointee. ``!nontemporal`` does not have any defined semantics for atomic loads.
The optional constant ``align`` argument specifies the alignment of the
operation (that is, the alignment of the memory address). A value of 0
@ -6972,18 +6971,16 @@ then the optimizer is not allowed to modify the number or order of
execution of this ``store`` with other :ref:`volatile
operations <volatile>`.
If the ``store`` is marked as ``atomic``, it takes an extra
:ref:`ordering <ordering>` and optional ``singlethread`` argument. The
``acquire`` and ``acq_rel`` orderings aren't valid on ``store``
instructions. Atomic loads produce :ref:`defined <memmodel>` results
when they may see multiple atomic stores. The type of the pointee must
be an integer or floating point type whose bit width is a power of two,
greater than or equal to eight, and less than or equal to a
target-specific size limit. ``align`` must be explicitly specified
on atomic stores, and the store has undefined behavior if the alignment
is not set to a value which is at least the size in bytes of the
pointee. ``!nontemporal`` does not have any defined semantics for
atomic stores.
If the ``store`` is marked as ``atomic``, it takes an extra :ref:`ordering
<ordering>` and optional ``singlethread`` argument. The ``acquire`` and
``acq_rel`` orderings aren't valid on ``store`` instructions. Atomic loads
produce :ref:`defined <memmodel>` results when they may see multiple atomic
stores. The type of the pointee must be an integer, pointer, or floating-point
type whose bit width is a power of two greater than or equal to eight and less
than or equal to a target-specific size limit. ``align`` must be explicitly
specified on atomic stores, and the store has undefined behavior if the
alignment is not set to a value which is at least the size in bytes of the
pointee. ``!nontemporal`` does not have any defined semantics for atomic stores.
The optional constant ``align`` argument specifies the alignment of the
operation (that is, the alignment of the memory address). A value of 0

49
lib/IR/Verifier.cpp
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@ -207,6 +207,8 @@ class Verifier : public InstVisitor<Verifier>, VerifierSupport {
/// Cache of constants visited in search of ConstantExprs.
SmallPtrSet<const Constant *, 32> ConstantExprVisited;
void checkAtomicMemAccessSize(const Module *M, Type *Ty,
const Instruction *I);
public:
explicit Verifier(raw_ostream &OS)
: VerifierSupport(OS), Context(nullptr), LandingPadResultTy(nullptr),
@ -2734,6 +2736,14 @@ void Verifier::visitRangeMetadata(Instruction& I,
}
}
void Verifier::checkAtomicMemAccessSize(const Module *M, Type *Ty,
const Instruction *I) {
unsigned Size = M->getDataLayout().getTypeSizeInBits(Ty);
Assert(Size >= 8, "atomic memory access' size must be byte-sized", Ty, I);
Assert(!(Size & (Size - 1)),
"atomic memory access' operand must have a power-of-two size", Ty, I);
}
void Verifier::visitLoadInst(LoadInst &LI) {
PointerType *PTy = dyn_cast<PointerType>(LI.getOperand(0)->getType());
Assert(PTy, "Load operand must be a pointer.", &LI);
@ -2745,15 +2755,12 @@ void Verifier::visitLoadInst(LoadInst &LI) {
"Load cannot have Release ordering", &LI);
Assert(LI.getAlignment() != 0,
"Atomic load must specify explicit alignment", &LI);
if (!ElTy->isPointerTy()) {
Assert(ElTy->isIntegerTy() || ElTy->isFloatingPointTy(),
"atomic load operand must have integer or floating point type!",
&LI, ElTy);
unsigned Size = ElTy->getPrimitiveSizeInBits();
Assert(Size >= 8 && !(Size & (Size - 1)),
"atomic load operand must be power-of-two byte-sized integer", &LI,
ElTy);
}
Assert(ElTy->isIntegerTy() || ElTy->isPointerTy() ||
ElTy->isFloatingPointTy(),
"atomic load operand must have integer, pointer, or floating point "
"type!",
ElTy, &LI);
checkAtomicMemAccessSize(M, ElTy, &LI);
} else {
Assert(LI.getSynchScope() == CrossThread,
"Non-atomic load cannot have SynchronizationScope specified", &LI);
@ -2775,15 +2782,12 @@ void Verifier::visitStoreInst(StoreInst &SI) {
"Store cannot have Acquire ordering", &SI);
Assert(SI.getAlignment() != 0,
"Atomic store must specify explicit alignment", &SI);
if (!ElTy->isPointerTy()) {
Assert(ElTy->isIntegerTy() || ElTy->isFloatingPointTy(),
"atomic store operand must have integer or floating point type!",
&SI, ElTy);
unsigned Size = ElTy->getPrimitiveSizeInBits();
Assert(Size >= 8 && !(Size & (Size - 1)),
"atomic store operand must be power-of-two byte-sized integer",
&SI, ElTy);
}
Assert(ElTy->isIntegerTy() || ElTy->isPointerTy() ||
ElTy->isFloatingPointTy(),
"atomic store operand must have integer, pointer, or floating point "
"type!",
ElTy, &SI);
checkAtomicMemAccessSize(M, ElTy, &SI);
} else {
Assert(SI.getSynchScope() == CrossThread,
"Non-atomic store cannot have SynchronizationScope specified", &SI);
@ -2830,9 +2834,7 @@ void Verifier::visitAtomicCmpXchgInst(AtomicCmpXchgInst &CXI) {
Type *ElTy = PTy->getElementType();
Assert(ElTy->isIntegerTy(), "cmpxchg operand must have integer type!", &CXI,
ElTy);
unsigned Size = ElTy->getPrimitiveSizeInBits();
Assert(Size >= 8 && !(Size & (Size - 1)),
"cmpxchg operand must be power-of-two byte-sized integer", &CXI, ElTy);
checkAtomicMemAccessSize(M, ElTy, &CXI);
Assert(ElTy == CXI.getOperand(1)->getType(),
"Expected value type does not match pointer operand type!", &CXI,
ElTy);
@ -2851,10 +2853,7 @@ void Verifier::visitAtomicRMWInst(AtomicRMWInst &RMWI) {
Type *ElTy = PTy->getElementType();
Assert(ElTy->isIntegerTy(), "atomicrmw operand must have integer type!",
&RMWI, ElTy);
unsigned Size = ElTy->getPrimitiveSizeInBits();
Assert(Size >= 8 && !(Size & (Size - 1)),
"atomicrmw operand must be power-of-two byte-sized integer", &RMWI,
ElTy);
checkAtomicMemAccessSize(M, ElTy, &RMWI);
Assert(ElTy == RMWI.getOperand(1)->getType(),
"Argument value type does not match pointer operand type!", &RMWI,
ElTy);

4
test/Verifier/atomics.ll
View File

@ -1,7 +1,7 @@
; RUN: not opt -verify < %s 2>&1 | FileCheck %s
; CHECK: atomic store operand must have integer or floating point type!
; CHECK: atomic load operand must have integer or floating point type!
; CHECK: atomic store operand must have integer, pointer, or floating point type!
; CHECK: atomic load operand must have integer, pointer, or floating point type!
define void @foo(x86_mmx* %P, x86_mmx %v) {
store atomic x86_mmx %v, x86_mmx* %P unordered, align 8