It's better to have the arrays, which would trigger the creation of stack

protectors, to be near the stack protectors on the stack. Accomplish this by
tagging the stack object with a predicate that indicates that it would trigger
this. In the prolog-epilog inserter, assign these objects to the stack after the
stack protector but before the other objects.

llvm-svn: 109481

3 files changed, 33 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/MachineFunction.cpp b/llvm/lib/CodeGen/MachineFunction.cpp
index 9a52b7b0b41..017170076ce 100644
--- a/llvm/lib/CodeGen/MachineFunction.cpp
+++ b/llvm/lib/CodeGen/MachineFunction.cpp
@@ -446,7 +446,7 @@ int MachineFrameInfo::CreateFixedObject(uint64_t Size, int64_t SPOffset,
   unsigned StackAlign = TFI.getStackAlignment();
   unsigned Align = MinAlign(SPOffset, StackAlign);
   Objects.insert(Objects.begin(), StackObject(Size, Align, SPOffset, Immutable,
-                                              /*isSS*/false));
+                                              /*isSS*/false, false));
   return -++NumFixedObjects;
 }
 
diff --git a/llvm/lib/CodeGen/PrologEpilogInserter.cpp b/llvm/lib/CodeGen/PrologEpilogInserter.cpp
index 3787d0b7bed..827b6a30ad5 100644
--- a/llvm/lib/CodeGen/PrologEpilogInserter.cpp
+++ b/llvm/lib/CodeGen/PrologEpilogInserter.cpp
@@ -33,6 +33,7 @@
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/ADT/IndexedMap.h"
+#include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/STLExtras.h"
 #include <climits>
 
@@ -549,10 +550,29 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
 
   // Make sure that the stack protector comes before the local variables on the
   // stack.
-  if (MFI->getStackProtectorIndex() >= 0)
+  SmallSet<int, 16> LargeStackObjs;
+  if (MFI->getStackProtectorIndex() >= 0) {
     AdjustStackOffset(MFI, MFI->getStackProtectorIndex(), StackGrowsDown,
                       Offset, MaxAlign);
 
+    // Assign large stack objects first.
+    for (unsigned i = 0, e = MFI->getObjectIndexEnd(); i != e; ++i) {
+      if (i >= MinCSFrameIndex && i <= MaxCSFrameIndex)
+        continue;
+      if (RS && (int)i == RS->getScavengingFrameIndex())
+        continue;
+      if (MFI->isDeadObjectIndex(i))
+        continue;
+      if (MFI->getStackProtectorIndex() == (int)i)
+        continue;
+      if (!MFI->MayNeedStackProtector(i))
+        continue;
+
+      AdjustStackOffset(MFI, i, StackGrowsDown, Offset, MaxAlign);
+      LargeStackObjs.insert(i);
+    }
+  }
+
   // Then assign frame offsets to stack objects that are not used to spill
   // callee saved registers.
   for (unsigned i = 0, e = MFI->getObjectIndexEnd(); i != e; ++i) {
@@ -564,6 +584,8 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
       continue;
     if (MFI->getStackProtectorIndex() == (int)i)
       continue;
+    if (LargeStackObjs.count(i))
+      continue;
 
     AdjustStackOffset(MFI, i, StackGrowsDown, Offset, MaxAlign);
   }
diff --git a/llvm/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp b/llvm/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
index ee3bc0abbcf..77a2c866966 100644
--- a/llvm/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
@@ -112,8 +112,16 @@ void FunctionLoweringInfo::set(const Function &fn, MachineFunction &mf) {
 
         TySize *= CUI->getZExtValue();   // Get total allocated size.
         if (TySize == 0) TySize = 1; // Don't create zero-sized stack objects.
+
+        // The object may need to be placed onto the stack near the stack
+        // protector if one exists. Determine here if this object is a suitable
+        // candidate. I.e., it would trigger the creation of a stack protector.
+        bool MayNeedSP =
+          (AI->isArrayAllocation() ||
+           (TySize > 8 && isa<ArrayType>(Ty) &&
+            cast<ArrayType>(Ty)->getElementType()->isIntegerTy(8)));
         StaticAllocaMap[AI] =
-          MF->getFrameInfo()->CreateStackObject(TySize, Align, false);
+          MF->getFrameInfo()->CreateStackObject(TySize, Align, false, MayNeedSP);
       }
 
   for (; BB != EB; ++BB)