[PATCH] D42710: [SafeStack] Use updated CreateMemCpy API to set more accurate source and destination alignments.

[Daniel Neilson via Phabricator via llvm-commits]

dneilson created this revision.
dneilson added a reviewer: eugenis.
Herald added a reviewer: bollu.

  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. ( https://reviews.llvm.org/rL322965, https://reviews.llvm.org/rC322964, https://reviews.llvm.org/rL322963 )
Step 2) Expand the IRBuilder API to allow creation of memcpy/memmove with differing
source and dest alignments. ( https://reviews.llvm.org/rL323597 )
Step 3) Update Clang to use the new IRBuilder API. ( https://reviews.llvm.org/rC323617 )
Step 4) Update Polly to use the new IRBuilder API. ( https://reviews.llvm.org/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


Repository:
  rL LLVM

https://reviews.llvm.org/D42710

Files:
  lib/CodeGen/SafeStack.cpp
  lib/CodeGen/SafeStackLayout.cpp
  lib/CodeGen/SafeStackLayout.h
  test/Transforms/SafeStack/X86/byval.ll


Index: test/Transforms/SafeStack/X86/byval.ll
===================================================================
--- test/Transforms/SafeStack/X86/byval.ll
+++ test/Transforms/SafeStack/X86/byval.ll
@@ -33,6 +33,23 @@
   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:
Index: lib/CodeGen/SafeStackLayout.h
===================================================================
--- lib/CodeGen/SafeStackLayout.h
+++ lib/CodeGen/SafeStackLayout.h
@@ -47,6 +47,7 @@
   SmallVector<StackObject, 8> StackObjects;
 
   DenseMap<const Value *, unsigned> ObjectOffsets;
+  DenseMap<const Value *, unsigned> ObjectAlignments;
 
   void layoutObject(StackObject &Obj);
 
@@ -64,6 +65,9 @@
   /// 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; }
 
Index: lib/CodeGen/SafeStackLayout.cpp
===================================================================
--- lib/CodeGen/SafeStackLayout.cpp
+++ lib/CodeGen/SafeStackLayout.cpp
@@ -42,6 +42,7 @@
 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);
 }
 
Index: lib/CodeGen/SafeStack.cpp
===================================================================
--- lib/CodeGen/SafeStack.cpp
+++ lib/CodeGen/SafeStack.cpp
@@ -557,6 +557,7 @@
 
   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 @@
                       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.


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