[PATCH] D152452: X86, PEI, WIP: Convert to backwards frame index elimination

[Jay Foad via Phabricator via llvm-commits]

foad updated this revision to Diff 546773.
foad added a comment.

Rebase.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D152452/new/

https://reviews.llvm.org/D152452

Files:
  llvm/lib/CodeGen/PrologEpilogInserter.cpp
  llvm/lib/Target/X86/X86InstrInfo.cpp
  llvm/lib/Target/X86/X86RegisterInfo.h


Index: llvm/lib/Target/X86/X86RegisterInfo.h
===================================================================
--- llvm/lib/Target/X86/X86RegisterInfo.h
+++ llvm/lib/Target/X86/X86RegisterInfo.h
@@ -143,6 +143,8 @@
                            int SPAdj, unsigned FIOperandNum,
                            RegScavenger *RS = nullptr) const override;
 
+  bool supportsBackwardScavenger() const override { return true; }
+
   /// findDeadCallerSavedReg - Return a caller-saved register that isn't live
   /// when it reaches the "return" instruction. We can then pop a stack object
   /// to this register without worry about clobbering it.
Index: llvm/lib/Target/X86/X86InstrInfo.cpp
===================================================================
--- llvm/lib/Target/X86/X86InstrInfo.cpp
+++ llvm/lib/Target/X86/X86InstrInfo.cpp
@@ -408,23 +408,23 @@
   }
 
   // To know whether a call adjusts the stack, we need information
-  // that is bound to the following ADJCALLSTACKUP pseudo.
-  // Look for the next ADJCALLSTACKUP that follows the call.
+  // that is bound to the preceding ADJCALLSTACKDOWN pseudo.
+  // Look for the next ADJCALLSTACKDOWN that precedes the call.
   if (MI.isCall()) {
     const MachineBasicBlock *MBB = MI.getParent();
-    auto I = ++MachineBasicBlock::const_iterator(MI);
-    for (auto E = MBB->end(); I != E; ++I) {
-      if (I->getOpcode() == getCallFrameDestroyOpcode() ||
+    auto I = MachineBasicBlock::const_iterator(MI);
+    for (auto E = MBB->begin(); I-- != E; ) {
+      if (I->getOpcode() == getCallFrameSetupOpcode() ||
           I->isCall())
         break;
     }
 
-    // If we could not find a frame destroy opcode, then it has already
+    // If we could not find a frame setup opcode, then it has already
     // been simplified, so we don't care.
-    if (I->getOpcode() != getCallFrameDestroyOpcode())
+    if (I->getOpcode() != getCallFrameSetupOpcode())
       return 0;
 
-    return -(I->getOperand(1).getImm());
+    return I->getOperand(1).getImm();
   }
 
   // Currently handle only PUSHes we can reasonably expect to see
Index: llvm/lib/CodeGen/PrologEpilogInserter.cpp
===================================================================
--- llvm/lib/CodeGen/PrologEpilogInserter.cpp
+++ llvm/lib/CodeGen/PrologEpilogInserter.cpp
@@ -1486,15 +1486,24 @@
   if (LocalRS)
     LocalRS->enterBasicBlockEnd(*BB);
 
+  bool InsideCallSequence = false;
   for (MachineBasicBlock::iterator I = BB->end(); I != BB->begin();) {
     MachineInstr &MI = *std::prev(I);
 
     if (TII.isFrameInstr(MI)) {
+      InsideCallSequence = !TII.isFrameSetup(MI);
       SPAdj -= TII.getSPAdjust(MI);
       TFI.eliminateCallFramePseudoInstr(MF, *BB, &MI);
       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(MI);
+
     // Step backwards to get the liveness state at (immedately after) MI.
     if (LocalRS)
       LocalRS->backward(MI);


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