Define a maximum supported alignment value for load, store, and

alloca instructions (constrained by their internal encoding),
and add error checking for it. Fix an instcombine bug which
generated huge alignment values (null is infinitely aligned).
This fixes undefined behavior noticed by John Regehr.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@109643 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 16 insertions, 1 deletions

diff --git a/lib/AsmParser/LLParser.cpp b/lib/AsmParser/LLParser.cpp
index 61b1ae5..e581a69 100644
--- a/lib/AsmParser/LLParser.cpp
+++ b/lib/AsmParser/LLParser.cpp
@@ -1154,6 +1154,8 @@ bool LLParser::ParseOptionalAlignment(unsigned &Alignment) {
   if (ParseUInt32(Alignment)) return true;
   if (!isPowerOf2_32(Alignment))
     return Error(AlignLoc, "alignment is not a power of two");
+  if (Alignment > MaximumAlignment)
+    return Error(AlignLoc, "huge alignments are not supported yet");
   return false;
 }
 
@@ -1176,6 +1178,7 @@ bool LLParser::ParseOptionalCommaAlign(unsigned &Alignment,
     if (Lex.getKind() != lltok::kw_align)
       return Error(Lex.getLoc(), "expected metadata or 'align'");
     
+    LocTy AlignLoc = Lex.getLoc();
     if (ParseOptionalAlignment(Alignment)) return true;
   }
 
diff --git a/lib/Transforms/InstCombine/InstCombineCalls.cpp b/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 0d5e302..fdb2dd6 100644
--- a/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -104,11 +104,15 @@ unsigned InstCombiner::GetOrEnforceKnownAlignment(Value *V,
   ComputeMaskedBits(V, Mask, KnownZero, KnownOne);
   unsigned TrailZ = KnownZero.countTrailingOnes();
 
-  // LLVM doesn't support alignments larger than this currently.
+  // Avoid trouble with rediculously large TrailZ values, such as
+  // those computed from a null pointer.
   TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1));
 
   unsigned Align = 1u << std::min(BitWidth - 1, TrailZ);
 
+  // LLVM doesn't support alignments larger than this currently.
+  Align = std::min(Align, MaximumAlignment);
+
   if (PrefAlign > Align)
     Align = EnforceKnownAlignment(V, Align, PrefAlign);
   
diff --git a/lib/VMCore/Instructions.cpp b/lib/VMCore/Instructions.cpp
index 57b7f3f..e03cc82 100644
--- a/lib/VMCore/Instructions.cpp
+++ b/lib/VMCore/Instructions.cpp
@@ -891,6 +891,8 @@ AllocaInst::~AllocaInst() {
 
 void AllocaInst::setAlignment(unsigned Align) {
   assert((Align & (Align-1)) == 0 && "Alignment is not a power of 2!");
+  assert(Align <= MaximumAlignment &&
+         "Alignment is greater than MaximumAlignment!");
   setInstructionSubclassData(Log2_32(Align) + 1);
   assert(getAlignment() == Align && "Alignment representation error!");
 }
@@ -1026,8 +1028,11 @@ LoadInst::LoadInst(Value *Ptr, const char *Name, bool isVolatile,
 
 void LoadInst::setAlignment(unsigned Align) {
   assert((Align & (Align-1)) == 0 && "Alignment is not a power of 2!");
+  assert(Align <= MaximumAlignment &&
+         "Alignment is greater than MaximumAlignment!");
   setInstructionSubclassData((getSubclassDataFromInstruction() & 1) |
                              ((Log2_32(Align)+1)<<1));
+  assert(getAlignment() == Align && "Alignment representation error!");
 }
 
 //===----------------------------------------------------------------------===//
@@ -1122,8 +1127,11 @@ StoreInst::StoreInst(Value *val, Value *addr, bool isVolatile,
 
 void StoreInst::setAlignment(unsigned Align) {
   assert((Align & (Align-1)) == 0 && "Alignment is not a power of 2!");
+  assert(Align <= MaximumAlignment &&
+         "Alignment is greater than MaximumAlignment!");
   setInstructionSubclassData((getSubclassDataFromInstruction() & 1) |
                              ((Log2_32(Align)+1) << 1));
+  assert(getAlignment() == Align && "Alignment representation error!");
 }
 
 //===----------------------------------------------------------------------===//