Stack Alignment: when creating stack objects in MachineFrameInfo, make sure

the alignment is clamped to TargetFrameLowering.getStackAlignment if the target
does not support stack realignment or the option "realign-stack" is off.

This will cause miscompile if the address is treated as aligned and add is
replaced with or in DAGCombine.

Added a bool StackRealignable to TargetFrameLowering to check whether stack
realignment is implemented for the target. Also added a bool RealignOption
to MachineFrameInfo to check whether the option "realign-stack" is on.

rdar://12713765


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169197 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 13 insertions, 3 deletions

diff --git a/include/llvm/CodeGen/MachineFrameInfo.h b/include/llvm/CodeGen/MachineFrameInfo.h
index bf75578fbc..93d77287d7 100644
--- a/include/llvm/CodeGen/MachineFrameInfo.h
+++ b/include/llvm/CodeGen/MachineFrameInfo.h
@@ -221,8 +221,11 @@ class MachineFrameInfo {
   /// just allocate them normally.
   bool UseLocalStackAllocationBlock;
 
+  /// Whether the "realign-stack" option is on.
+  bool RealignOption;
 public:
-    explicit MachineFrameInfo(const TargetFrameLowering &tfi) : TFI(tfi) {
+    explicit MachineFrameInfo(const TargetFrameLowering &tfi, bool RealignOpt)
+    : TFI(tfi), RealignOption(RealignOpt) {
     StackSize = NumFixedObjects = OffsetAdjustment = MaxAlignment = 0;
     HasVarSizedObjects = false;
     FrameAddressTaken = false;
diff --git a/include/llvm/Target/TargetFrameLowering.h b/include/llvm/Target/TargetFrameLowering.h
index 7e54f1447e..1958f90f9b 100644
--- a/include/llvm/Target/TargetFrameLowering.h
+++ b/include/llvm/Target/TargetFrameLowering.h
@@ -47,11 +47,12 @@ private:
   unsigned StackAlignment;
   unsigned TransientStackAlignment;
   int LocalAreaOffset;
+  bool StackRealignable;
 public:
   TargetFrameLowering(StackDirection D, unsigned StackAl, int LAO,
-                      unsigned TransAl = 1)
+                      unsigned TransAl = 1, bool StackReal = true)
     : StackDir(D), StackAlignment(StackAl), TransientStackAlignment(TransAl),
-      LocalAreaOffset(LAO) {}
+      LocalAreaOffset(LAO), StackRealignable(StackReal) {}
 
   virtual ~TargetFrameLowering();
 
@@ -76,6 +77,12 @@ public:
     return TransientStackAlignment;
   }
 
+  /// isStackRealignable - This method returns whether the stack can be
+  /// realigned.
+  bool isStackRealignable() const {
+    return StackRealignable;
+  }
+
   /// getOffsetOfLocalArea - This method returns the offset of the local area
   /// from the stack pointer on entrance to a function.
   ///