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Document the maximum LLVM IR alignment, which is 1 << 29 or 0.5 GiB

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Add verifier checks.  We already check these in the assembly parser, but
a frontend producing IR in memory wouldn't hit those checks.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213027 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Reid Kleckner 2014-07-15 01:16:09 +00:00
parent 7137eb36e1
commit cbebdef6eb
2 changed files with 16 additions and 6 deletions
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14
docs/LangRef.rst
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@ -582,7 +582,7 @@ to over-align the global if the global has an assigned section. In this
case, the extra alignment could be observable: for example, code could
assume that the globals are densely packed in their section and try to
iterate over them as an array, alignment padding would break this
iteration.
iteration. The maximum alignment is ``1 << 29``.
Globals can also have a :ref:`DLL storage class <dllstorageclass>`.
@ -4925,9 +4925,10 @@ bytes of memory on the runtime stack, returning a pointer of the
appropriate type to the program. If "NumElements" is specified, it is
the number of elements allocated, otherwise "NumElements" is defaulted
to be one. If a constant alignment is specified, the value result of the
allocation is guaranteed to be aligned to at least that boundary. If not
specified, or if zero, the target can choose to align the allocation on
any convenient boundary compatible with the type.
allocation is guaranteed to be aligned to at least that boundary. The
alignment may not be greater than ``1 << 29``. If not specified, or if
zero, the target can choose to align the allocation on any convenient
boundary compatible with the type.
'``type``' may be any sized type.
@ -5001,7 +5002,8 @@ or an omitted ``align`` argument means that the operation has the ABI
alignment for the target. It is the responsibility of the code emitter
to ensure that the alignment information is correct. Overestimating the
alignment results in undefined behavior. Underestimating the alignment
may produce less efficient code. An alignment of 1 is always safe.
may produce less efficient code. An alignment of 1 is always safe. The
maximum possible alignment is ``1 << 29``.
The optional ``!nontemporal`` metadata must reference a single
metadata name ``<index>`` corresponding to a metadata node with one
@ -5087,7 +5089,7 @@ alignment for the target. It is the responsibility of the code emitter
to ensure that the alignment information is correct. Overestimating the
alignment results in undefined behavior. Underestimating the
alignment may produce less efficient code. An alignment of 1 is always
safe.
safe. The maximum possible alignment is ``1 << 29``.
The optional ``!nontemporal`` metadata must reference a single metadata
name ``<index>`` corresponding to a metadata node with one ``i32`` entry of

8
lib/IR/Verifier.cpp
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@ -380,6 +380,8 @@ void Verifier::visitGlobalValue(const GlobalValue &GV) {
"Global is external, but doesn't have external or weak linkage!",
&GV);
Assert1(GV.getAlignment() <= Value::MaximumAlignment,
"huge alignment values are unsupported", &GV);
Assert1(!GV.hasAppendingLinkage() || isa<GlobalVariable>(GV),
"Only global variables can have appending linkage!", &GV);
@ -1891,6 +1893,8 @@ void Verifier::visitLoadInst(LoadInst &LI) {
Type *ElTy = PTy->getElementType();
Assert2(ElTy == LI.getType(),
"Load result type does not match pointer operand type!", &LI, ElTy);
Assert1(LI.getAlignment() <= Value::MaximumAlignment,
"huge alignment values are unsupported", &LI);
if (LI.isAtomic()) {
Assert1(LI.getOrdering() != Release && LI.getOrdering() != AcquireRelease,
"Load cannot have Release ordering", &LI);
@ -1966,6 +1970,8 @@ void Verifier::visitStoreInst(StoreInst &SI) {
Assert2(ElTy == SI.getOperand(0)->getType(),
"Stored value type does not match pointer operand type!",
&SI, ElTy);
Assert1(SI.getAlignment() <= Value::MaximumAlignment,
"huge alignment values are unsupported", &SI);
if (SI.isAtomic()) {
Assert1(SI.getOrdering() != Acquire && SI.getOrdering() != AcquireRelease,
"Store cannot have Acquire ordering", &SI);
@ -1997,6 +2003,8 @@ void Verifier::visitAllocaInst(AllocaInst &AI) {
&AI);
Assert1(AI.getArraySize()->getType()->isIntegerTy(),
"Alloca array size must have integer type", &AI);
Assert1(AI.getAlignment() <= Value::MaximumAlignment,
"huge alignment values are unsupported", &AI);
visitInstruction(AI);
}