[llvm] r213027 - Document the maximum LLVM IR alignment, which is 1 << 29 or 0.5 GiB

[Reid Kleckner]

Author: rnk
Date: Mon Jul 14 20:16:09 2014
New Revision: 213027

URL: http://llvm.org/viewvc/llvm-project?rev=213027&view=rev
Log:
Document the maximum LLVM IR alignment, which is 1 << 29 or 0.5 GiB

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

Modified:
    llvm/trunk/docs/LangRef.rst
    llvm/trunk/lib/IR/Verifier.cpp

Modified: llvm/trunk/docs/LangRef.rst
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/LangRef.rst?rev=213027&r1=213026&r2=213027&view=diff
==============================================================================
--- llvm/trunk/docs/LangRef.rst (original)
+++ llvm/trunk/docs/LangRef.rst Mon Jul 14 20:16:09 2014
@@ -582,7 +582,7 @@ to over-align the global if the global h
 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, re
 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 t
 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 resp
 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

Modified: llvm/trunk/lib/IR/Verifier.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/Verifier.cpp?rev=213027&r1=213026&r2=213027&view=diff
==============================================================================
--- llvm/trunk/lib/IR/Verifier.cpp (original)
+++ llvm/trunk/lib/IR/Verifier.cpp Mon Jul 14 20:16:09 2014
@@ -380,6 +380,8 @@ void Verifier::visitGlobalValue(const Gl
           "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 &L
   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
   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(AllocaIns
           &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);
 }