HHVM calling conventions.

HHVM calling convention, hhvmcc, is used by HHVM JIT for
functions in translated cache. We currently support LLVM back end to
generate code for X86-64 and may support other architectures in the
future.

In HHVM calling convention any GP register could be used to pass and
return values, with the exception of R12 which is reserved for
thread-local area and is callee-saved. Other than R12, we always
pass RBX and RBP as args, which are our virtual machine's stack pointer
and frame pointer respectively.

When we enter translation cache via hhvmcc function, we expect
the stack to be aligned at 16 bytes, i.e. skewed by 8 bytes as opposed
to standard ABI alignment. This affects stack object alignment and stack
adjustments for function calls.

One extra calling convention, hhvm_ccc, is used to call C++ helpers from
HHVM's translation cache. It is almost identical to standard C calling
convention with an exception of first argument which is passed in RBP
(before we use RDI, RSI, etc.)

Differential Revision: http://reviews.llvm.org/D12681

llvm-svn: 248832

1 files changed, 18 insertions, 15 deletions

diff --git a/llvm/lib/CodeGen/PrologEpilogInserter.cpp b/llvm/lib/CodeGen/PrologEpilogInserter.cpp
index c7398ad00a0..63825b5dde9 100644
--- a/llvm/lib/CodeGen/PrologEpilogInserter.cpp
+++ b/llvm/lib/CodeGen/PrologEpilogInserter.cpp
@@ -500,7 +500,7 @@ void PEI::insertCSRSpillsAndRestores(MachineFunction &Fn) {
 static inline void
 AdjustStackOffset(MachineFrameInfo *MFI, int FrameIdx,
                   bool StackGrowsDown, int64_t &Offset,
-                  unsigned &MaxAlign) {
+                  unsigned &MaxAlign, unsigned Skew) {
   // If the stack grows down, add the object size to find the lowest address.
   if (StackGrowsDown)
     Offset += MFI->getObjectSize(FrameIdx);
@@ -512,7 +512,7 @@ AdjustStackOffset(MachineFrameInfo *MFI, int FrameIdx,
   MaxAlign = std::max(MaxAlign, Align);
 
   // Adjust to alignment boundary.
-  Offset = RoundUpToAlignment(Offset, Align);
+  Offset = RoundUpToAlignment(Offset, Align, Skew);
 
   if (StackGrowsDown) {
     DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") at SP[" << -Offset << "]\n");
@@ -530,12 +530,12 @@ static void
 AssignProtectedObjSet(const StackObjSet &UnassignedObjs,
                       SmallSet<int, 16> &ProtectedObjs,
                       MachineFrameInfo *MFI, bool StackGrowsDown,
-                      int64_t &Offset, unsigned &MaxAlign) {
+                      int64_t &Offset, unsigned &MaxAlign, unsigned Skew) {
 
   for (StackObjSet::const_iterator I = UnassignedObjs.begin(),
         E = UnassignedObjs.end(); I != E; ++I) {
     int i = *I;
-    AdjustStackOffset(MFI, i, StackGrowsDown, Offset, MaxAlign);
+    AdjustStackOffset(MFI, i, StackGrowsDown, Offset, MaxAlign, Skew);
     ProtectedObjs.insert(i);
   }
 }
@@ -563,6 +563,9 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
          && "Local area offset should be in direction of stack growth");
   int64_t Offset = LocalAreaOffset;
 
+  // Skew to be applied to alignment.
+  unsigned Skew = TFI.getStackAlignmentSkew(Fn);
+
   // If there are fixed sized objects that are preallocated in the local area,
   // non-fixed objects can't be allocated right at the start of local area.
   // We currently don't support filling in holes in between fixed sized
@@ -593,7 +596,7 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
 
       unsigned Align = MFI->getObjectAlignment(i);
       // Adjust to alignment boundary
-      Offset = RoundUpToAlignment(Offset, Align);
+      Offset = RoundUpToAlignment(Offset, Align, Skew);
 
       MFI->setObjectOffset(i, -Offset);        // Set the computed offset
     }
@@ -602,7 +605,7 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
     for (int i = MaxCSFI; i >= MinCSFI ; --i) {
       unsigned Align = MFI->getObjectAlignment(i);
       // Adjust to alignment boundary
-      Offset = RoundUpToAlignment(Offset, Align);
+      Offset = RoundUpToAlignment(Offset, Align, Skew);
 
       MFI->setObjectOffset(i, Offset);
       Offset += MFI->getObjectSize(i);
@@ -624,7 +627,7 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
     RS->getScavengingFrameIndices(SFIs);
     for (SmallVectorImpl<int>::iterator I = SFIs.begin(),
            IE = SFIs.end(); I != IE; ++I)
-      AdjustStackOffset(MFI, *I, StackGrowsDown, Offset, MaxAlign);
+      AdjustStackOffset(MFI, *I, StackGrowsDown, Offset, MaxAlign, Skew);
   }
 
   // FIXME: Once this is working, then enable flag will change to a target
@@ -635,7 +638,7 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
     unsigned Align = MFI->getLocalFrameMaxAlign();
 
     // Adjust to alignment boundary.
-    Offset = RoundUpToAlignment(Offset, Align);
+    Offset = RoundUpToAlignment(Offset, Align, Skew);
 
     DEBUG(dbgs() << "Local frame base offset: " << Offset << "\n");
 
@@ -662,7 +665,7 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
     StackObjSet AddrOfObjs;
 
     AdjustStackOffset(MFI, MFI->getStackProtectorIndex(), StackGrowsDown,
-                      Offset, MaxAlign);
+                      Offset, MaxAlign, Skew);
 
     // Assign large stack objects first.
     for (unsigned i = 0, e = MFI->getObjectIndexEnd(); i != e; ++i) {
@@ -695,11 +698,11 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
     }
 
     AssignProtectedObjSet(LargeArrayObjs, ProtectedObjs, MFI, StackGrowsDown,
-                          Offset, MaxAlign);
+                          Offset, MaxAlign, Skew);
     AssignProtectedObjSet(SmallArrayObjs, ProtectedObjs, MFI, StackGrowsDown,
-                          Offset, MaxAlign);
+                          Offset, MaxAlign, Skew);
     AssignProtectedObjSet(AddrOfObjs, ProtectedObjs, MFI, StackGrowsDown,
-                          Offset, MaxAlign);
+                          Offset, MaxAlign, Skew);
   }
 
   // Then assign frame offsets to stack objects that are not used to spill
@@ -719,7 +722,7 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
     if (ProtectedObjs.count(i))
       continue;
 
-    AdjustStackOffset(MFI, i, StackGrowsDown, Offset, MaxAlign);
+    AdjustStackOffset(MFI, i, StackGrowsDown, Offset, MaxAlign, Skew);
   }
 
   // Make sure the special register scavenging spill slot is closest to the
@@ -729,7 +732,7 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
     RS->getScavengingFrameIndices(SFIs);
     for (SmallVectorImpl<int>::iterator I = SFIs.begin(),
            IE = SFIs.end(); I != IE; ++I)
-      AdjustStackOffset(MFI, *I, StackGrowsDown, Offset, MaxAlign);
+      AdjustStackOffset(MFI, *I, StackGrowsDown, Offset, MaxAlign, Skew);
   }
 
   if (!TFI.targetHandlesStackFrameRounding()) {
@@ -754,7 +757,7 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
     // If the frame pointer is eliminated, all frame offsets will be relative to
     // SP not FP. Align to MaxAlign so this works.
     StackAlign = std::max(StackAlign, MaxAlign);
-    Offset = RoundUpToAlignment(Offset, StackAlign);
+    Offset = RoundUpToAlignment(Offset, StackAlign, Skew);
   }
 
   // Update frame info to pretend that this is part of the stack...