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

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. (rL323886, rL323891, rL324148, rL324273, rL324278,
rL324384, rL324395, rL324402, rL324626, rL324642, rL324653, rL324654, rL324773, rL324774,
rL324781, rL324784 )
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

Reviewers: eugenis, bollu

Reviewed By: eugenis

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D42710

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@324955 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/SafeStack.cpp

@@ -557,6 +557,7 @@ Value *SafeStack::moveStaticAllocasToUnsafeStack(
 
   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);
@@ -573,7 +574,7 @@ Value *SafeStack::moveStaticAllocasToUnsafeStack(
                       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.

lib/CodeGen/SafeStackLayout.cpp

@@ -42,6 +42,7 @@ LLVM_DUMP_METHOD void StackLayout::print(raw_ostream &OS) {
 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);
 }
 

lib/CodeGen/SafeStackLayout.h

@@ -47,6 +47,7 @@ class StackLayout {
   SmallVector<StackObject, 8> StackObjects;
 
   DenseMap<const Value *, unsigned> ObjectOffsets;
+  DenseMap<const Value *, unsigned> ObjectAlignments;
 
   void layoutObject(StackObject &Obj);
 
@@ -64,6 +65,9 @@ public:
   /// 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; }
 

test/Transforms/SafeStack/X86/byval.ll

@@ -33,6 +33,23 @@ entry:
   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: