[SafeStack] Use updated CreateMemCpy API to set more accurate source and destination alignments.

[dneilson]

Summary

This change is part of step five in the series of changes to remove alignment argument from

memcpy/memmove/memset in favour of alignment attributes. In particular, this changes the
creation of memcpys in the SafeStack pass to set the alignment of the destination object to
its stack alignment while separately setting the source byval arguments alignment to its
alignment.

Steps:
Step 1) Remove alignment parameter and create alignment parameter attributes for
memcpy/memmove/memset. ( rL322965, rC322964, rL322963 )
Step 2) Expand the IRBuilder API to allow creation of memcpy/memmove with differing
source and dest alignments. ( rL323597 )
Step 3) Update Clang to use the new IRBuilder API. ( rC323617 )
Step 4) Update Polly to use the new IRBuilder API. ( rL323618 )
Step 5) Update LLVM passes that create memcpy/memmove calls to use the new IRBuilder API,
and those that use use MemIntrinsicInst::[get|set]Alignment() to use [get|set]DestAlignment()
and [get|set]SourceAlignment() instead.
Step 6) Remove the single-alignment IRBuilder API for memcpy/memmove, and the
MemIntrinsicInst::[get|set]Alignment() methods.

Reference

http://lists.llvm.org/pipermail/llvm-dev/2015-August/089384.html
http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20151109/312083.html

[dneilson]

ping

[eugenis]

LGTM, thank you!

lib/CodeGen/SafeStack.cpp

if (StackGuardSlot) {
 
     // Replace alloc with the new location.
     StackGuardSlot->replaceAllUsesWith(NewAI);
     StackGuardSlot->eraseFromParent();
   }
 
   for (Argument *Arg : ByValArguments) {
     unsigned Offset = SSL.getObjectOffset(Arg);
+    unsigned Align = SSL.getObjectAlignment(Arg);
     Type *Ty = Arg->getType()->getPointerElementType();
 
     uint64_t Size = DL.getTypeStoreSize(Ty);
     if (Size == 0)
       Size = 1; // Don't create zero-sized stack objects.
 
     Value *Off = IRB.CreateGEP(BasePointer, // BasePointer is i8*
                                ConstantInt::get(Int32Ty, -Offset));
     Value *NewArg = IRB.CreateBitCast(Off, Arg->getType(),
                                      Arg->getName() + ".unsafe-byval");
 
     // Replace alloc with the new location.
     replaceDbgDeclare(Arg, BasePointer, BasePointer->getNextNode(), DIB,
                       DIExpression::NoDeref, -Offset, DIExpression::NoDeref);
     Arg->replaceAllUsesWith(NewArg);
     IRB.SetInsertPoint(cast<Instruction>(NewArg)->getNextNode());
-    IRB.CreateMemCpy(Off, Arg, Size, Arg->getParamAlignment());
+    IRB.CreateMemCpy(Off, Align, Arg, Arg->getParamAlignment(), Size);
   }
 
   // Allocate space for every unsafe static AllocaInst on the unsafe stack.
   for (AllocaInst *AI : StaticAllocas) {
     IRB.SetInsertPoint(AI);
     unsigned Offset = SSL.getObjectOffset(AI);
 
     uint64_t Size = getStaticAllocaAllocationSize(AI);

lib/CodeGen/SafeStackLayout.h

struct StackObject {
     const Value *Handle;
     unsigned Size, Alignment;
     StackColoring::LiveRange Range;
   };
 
   SmallVector<StackObject, 8> StackObjects;
 
   DenseMap<const Value *, unsigned> ObjectOffsets;
+  DenseMap<const Value *, unsigned> ObjectAlignments;
 
   void layoutObject(StackObject &Obj);
 
 public:
   StackLayout(unsigned StackAlignment) : MaxAlignment(StackAlignment) {}
 
   /// Add an object to the stack frame. Value pointer is opaque and used as a
   /// handle to retrieve the object's offset in the frame later.
   void addObject(const Value *V, unsigned Size, unsigned Alignment,
                  const StackColoring::LiveRange &Range);
 
   /// Run the layout computation for all previously added objects.
   void computeLayout();
 
   /// Returns the offset to the object start in the stack frame.
   unsigned getObjectOffset(const Value *V) { return ObjectOffsets[V]; }
 
+  /// Returns the alignment of the object
+  unsigned getObjectAlignment(const Value *V) { return ObjectAlignments[V]; }
+
   /// Returns the size of the entire frame.
   unsigned getFrameSize() { return Regions.empty() ? 0 : Regions.back().End; }
 
   /// Returns the alignment of the frame.
   unsigned getFrameAlignment() { return MaxAlignment; }
 
   void print(raw_ostream &OS);
 };
 
 } // end namespace safestack
 
 } // end namespace llvm
 
 #endif // LLVM_LIB_CODEGEN_SAFESTACKLAYOUT_H

lib/CodeGen/SafeStackLayout.cpp

LLVM_DUMP_METHOD void StackLayout::print(raw_ostream &OS) {
   for (auto &IT : ObjectOffsets) {
     OS << "  at " << IT.getSecond() << ": " << *IT.getFirst() << "\n";
   }
 }
 
 void StackLayout::addObject(const Value *V, unsigned Size, unsigned Alignment,
                             const StackColoring::LiveRange &Range) {
   StackObjects.push_back({V, Size, Alignment, Range});
+  ObjectAlignments[V] = Alignment;
   MaxAlignment = std::max(MaxAlignment, Alignment);
 }
 
 static unsigned AdjustStackOffset(unsigned Offset, unsigned Size,
                                   unsigned Alignment) {
   return alignTo(Offset + Size, Alignment) - Size;
 }
 

test/Transforms/SafeStack/X86/byval.ll

entry:
   ; CHECK: %[[C:.*]] = bitcast %struct.S* %zzz to i8*
   ; CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 8 %[[B]], i8* align 8 %[[C]], i64 400, i1 false)
   ; CHECK: ret i32
   %arrayidx = getelementptr inbounds %struct.S, %struct.S* %zzz, i64 0, i32 0, i64 %idx
   %0 = load i32, i32* %arrayidx, align 4
   ret i32 %0
 }
 
+; Unsafe access to a byval argument.
+; Argument is copied to the unsafe stack.
+; Check that dest align of memcpy is set according to datalayout prefered alignment
+define i32 @ByValUnsafe2(%struct.S* byval nocapture readonly %zzz, i64 %idx) norecurse nounwind readonly safestack uwtable {
+entry:
+  ; CHECK-LABEL: @ByValUnsafe
+  ; CHECK: %[[A:.*]] = load {{.*}} @__safestack_unsafe_stack_ptr
+  ; CHECK: store {{.*}} @__safestack_unsafe_stack_ptr
+  ; CHECK: %[[B:.*]] = getelementptr i8, i8* %[[A]], i32 -400
+  ; CHECK: %[[C:.*]] = bitcast %struct.S* %zzz to i8*
+  ; CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 8 %[[B]], i8* %[[C]], i64 400, i1 false)
+  ; CHECK: ret i32
+  %arrayidx = getelementptr inbounds %struct.S, %struct.S* %zzz, i64 0, i32 0, i64 %idx
+  %0 = load i32, i32* %arrayidx, align 4
+  ret i32 %0
+}
+
 ; Highly aligned byval argument.
 define i32 @ByValUnsafeAligned(%struct.S* byval nocapture readonly align 64 %zzz, i64 %idx) norecurse nounwind readonly safestack uwtable {
 entry:
   ; CHECK-LABEL: @ByValUnsafeAligned
   ; CHECK: %[[A:.*]] = load {{.*}} @__safestack_unsafe_stack_ptr
   ; CHECK: %[[B:.*]] = ptrtoint i8* %[[A]] to i64
   ; CHECK: and i64 %[[B]], -64
   ; CHECK: ret i32
   %arrayidx = getelementptr inbounds %struct.S, %struct.S* %zzz, i64 0, i32 0, i64 0
   %0 = load i32, i32* %arrayidx, align 64
   %arrayidx2 = getelementptr inbounds %struct.S, %struct.S* %zzz, i64 0, i32 0, i64 %idx
   %1 = load i32, i32* %arrayidx2, align 4
   %add = add nsw i32 %1, %0
   ret i32 %add
 }