Move SPAdj logic from PEI into the targets (NFC)

PEI tries to keep track of how much starting or ending a call sequence adjusts the stack pointer by, so that it can resolve frame-index references. Currently, it takes a very simplistic view of how SP adjustments are done - both FrameStartOpcode and FrameDestroyOpcode adjust it exactly by the amount written in its first argument.

This view is in fact incorrect for some targets (e.g. due to stack re-alignment, or because it may want to adjust the stack pointer in multiple steps). However, that doesn't cause breakage, because most targets (the only in-tree exception appears to be 32-bit ARM) rely on being able to simplify the call frame pseudo-instructions earlier, so this code is never hit. 

Moving the computation into TargetInstrInfo allows targets to override the way the adjustment is computed if they need to have a non-zero SPAdj.

Differential Revision: http://reviews.llvm.org/D6863

llvm-svn: 225437

llvm/include/llvm/Target/TargetInstrInfo.h

@@ -109,6 +109,12 @@ class TargetInstrInfo : public MCInstrInfo {
   int getCallFrameSetupOpcode() const { return CallFrameSetupOpcode; }
   int getCallFrameDestroyOpcode() const { return CallFrameDestroyOpcode; }
 
+  /// Returns the actual stack pointer adjustment made by an instruction
+  /// as part of a call sequence. By default, only call frame setup/destroy
+  /// instructions adjust the stack, but targets may want to override this
+  /// to enable more fine-grained adjustment, or adjust by a different value.
+  virtual int getSPAdjust(const MachineInstr *MI) const;
+
   /// isCoalescableExtInstr - Return true if the instruction is a "coalescable"
   /// extension instruction. That is, it's like a copy where it's legal for the
   /// source to overlap the destination. e.g. X86::MOVSX64rr32. If this returns

llvm/lib/CodeGen/PrologEpilogInserter.cpp

@@ -743,26 +743,19 @@ void PEI::replaceFrameIndices(MachineBasicBlock *BB, MachineFunction &Fn,
   const TargetInstrInfo &TII = *Fn.getSubtarget().getInstrInfo();
   const TargetRegisterInfo &TRI = *Fn.getSubtarget().getRegisterInfo();
   const TargetFrameLowering *TFI = Fn.getSubtarget().getFrameLowering();
-  bool StackGrowsDown =
-    TFI->getStackGrowthDirection() == TargetFrameLowering::StackGrowsDown;
   int FrameSetupOpcode   = TII.getCallFrameSetupOpcode();
   int FrameDestroyOpcode = TII.getCallFrameDestroyOpcode();
 
   if (RS && !FrameIndexVirtualScavenging) RS->enterBasicBlock(BB);
 
+  bool InsideCallSequence = false;
+
   for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ) {
 
     if (I->getOpcode() == FrameSetupOpcode ||
         I->getOpcode() == FrameDestroyOpcode) {
-      // Remember how much SP has been adjusted to create the call
-      // frame.
-      int Size = I->getOperand(0).getImm();
-
-      if ((!StackGrowsDown && I->getOpcode() == FrameSetupOpcode) ||
-          (StackGrowsDown && I->getOpcode() == FrameDestroyOpcode))
-        Size = -Size;
-
-      SPAdj += Size;
+      InsideCallSequence = (I->getOpcode() == FrameSetupOpcode);
+      SPAdj += TII.getSPAdjust(I);
 
       MachineBasicBlock::iterator PrevI = BB->end();
       if (I != BB->begin()) PrevI = std::prev(I);
@@ -776,6 +769,13 @@ void PEI::replaceFrameIndices(MachineBasicBlock *BB, MachineFunction &Fn,
       continue;
     }
 
+    // If we are looking at a call sequence, we need to keep track of
+    // the SP adjustment made by each instruction in the sequence.
+    // This includes both the frame setup/destroy pseudos (handled above),
+    // as well as other instructions that have side effects w.r.t the SP.
+    if (InsideCallSequence)
+      SPAdj += TII.getSPAdjust(I);
+
     MachineInstr *MI = I;
     bool DoIncr = true;
     for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {

llvm/lib/CodeGen/TargetInstrInfo.cpp

@@ -28,6 +28,7 @@
 #include "llvm/Target/TargetLowering.h"
 #include "llvm/Target/TargetMachine.h"
 #include "llvm/Target/TargetRegisterInfo.h"
+#include "llvm/Target/TargetFrameLowering.h"
 #include <cctype>
 using namespace llvm;
 
@@ -644,6 +645,28 @@ isReallyTriviallyReMaterializableGeneric(const MachineInstr *MI,
   return true;
 }
 
+int TargetInstrInfo::getSPAdjust(const MachineInstr *MI) const {
+  const MachineFunction *MF = MI->getParent()->getParent();
+  const TargetFrameLowering *TFI = MF->getSubtarget().getFrameLowering();
+  bool StackGrowsDown =
+    TFI->getStackGrowthDirection() == TargetFrameLowering::StackGrowsDown;
+
+  int FrameSetupOpcode = getCallFrameSetupOpcode();
+  int FrameDestroyOpcode = getCallFrameDestroyOpcode();
+
+  if (MI->getOpcode() != FrameSetupOpcode &&
+      MI->getOpcode() != FrameDestroyOpcode)
+    return 0;
+
+  int SPAdj = MI->getOperand(0).getImm();
+
+  if ((!StackGrowsDown && MI->getOpcode() == FrameSetupOpcode) ||
+       (StackGrowsDown && MI->getOpcode() == FrameDestroyOpcode))
+    SPAdj = -SPAdj;
+
+  return SPAdj;
+}
+
 /// isSchedulingBoundary - Test if the given instruction should be
 /// considered a scheduling boundary. This primarily includes labels
 /// and terminators.