From b827123cf796571f5f00d7b5a0006dd9aff3fa0e Mon Sep 17 00:00:00 2001
From: Manman Ren <mren@apple.com>
Date: Mon, 15 Jul 2013 23:47:29 +0000
Subject: PEI: Support for non-zero SPAdj at beginning of a basic block.

We can have a FrameSetup in one basic block and the matching FrameDestroy
in a different basic block when we have struct byval. In that case, SPAdj
is not zero at beginning of the basic block.

Modify PEI to correctly set SPAdj at beginning of each basic block using
DFS traversal. We used to assume SPAdj is 0 at beginning of each basic block.

PEI had an assert SPAdjCount || SPAdj == 0.
If we have a Destroy <n> followed by a Setup <m>, PEI will assert failure.
We can add an extra condition to make sure the pairs are matched:
  The pairs start with a FrameSetup.
But since we are doing a much better job in the verifier, this patch removes
the check in PEI.

PR16393

llvm-svn: 186364
---
 llvm/lib/CodeGen/PrologEpilogInserter.cpp | 41 ++++++++++++++++++++-----------
 1 file changed, 26 insertions(+), 15 deletions(-)

(limited to 'llvm/lib/CodeGen/PrologEpilogInserter.cpp')

diff --git a/llvm/lib/CodeGen/PrologEpilogInserter.cpp b/llvm/lib/CodeGen/PrologEpilogInserter.cpp
index b39cd529c47..1965188eb0f 100644
--- a/llvm/lib/CodeGen/PrologEpilogInserter.cpp
+++ b/llvm/lib/CodeGen/PrologEpilogInserter.cpp
@@ -728,7 +728,33 @@ void PEI::insertPrologEpilogCode(MachineFunction &Fn) {
 void PEI::replaceFrameIndices(MachineFunction &Fn) {
   if (!Fn.getFrameInfo()->hasStackObjects()) return; // Nothing to do?
 
+  // Store SPAdj at exit of a basic block.
+  SmallVector<int, 8> SPState;
+  SPState.resize(Fn.getNumBlockIDs());
+  SmallPtrSet<MachineBasicBlock*, 8> Reachable;
+
+  // Iterate over the reachable blocks in DFS order.
+  for (df_ext_iterator<MachineFunction*, SmallPtrSet<MachineBasicBlock*, 8> >
+       DFI = df_ext_begin(&Fn, Reachable), DFE = df_ext_end(&Fn, Reachable);
+       DFI != DFE; ++DFI) {
+    int SPAdj = 0;
+    // Check the exit state of the DFS stack predecessor.
+    if (DFI.getPathLength() >= 2) {
+      MachineBasicBlock *StackPred = DFI.getPath(DFI.getPathLength() - 2);
+      assert(Reachable.count(StackPred) &&
+             "DFS stack predecessor is already visited.\n");
+      SPAdj = SPState[StackPred->getNumber()];
+    }
+    MachineBasicBlock *BB = *DFI;
+    replaceFrameIndices(BB, Fn, SPAdj);
+    SPState[BB->getNumber()] = SPAdj;
+  }
+
+  // Handle the unreachable blocks.
   for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) {
+    if (Reachable.count(BB))
+      // Already handled in DFS traversal.
+      continue;
     int SPAdj = 0;
     replaceFrameIndices(BB, Fn, SPAdj);
   }
@@ -746,19 +772,12 @@ void PEI::replaceFrameIndices(MachineBasicBlock *BB, MachineFunction &Fn,
   int FrameSetupOpcode   = TII.getCallFrameSetupOpcode();
   int FrameDestroyOpcode = TII.getCallFrameDestroyOpcode();
 
-#ifndef NDEBUG
-  int SPAdjCount = 0; // frame setup / destroy count.
-#endif
   if (RS && !FrameIndexVirtualScavenging) RS->enterBasicBlock(BB);
 
   for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ) {
 
     if (I->getOpcode() == FrameSetupOpcode ||
         I->getOpcode() == FrameDestroyOpcode) {
-#ifndef NDEBUG
-      // Track whether we see even pairs of them
-      SPAdjCount += I->getOpcode() == FrameSetupOpcode ? 1 : -1;
-#endif
       // Remember how much SP has been adjusted to create the call
       // frame.
       int Size = I->getOperand(0).getImm();
@@ -833,14 +852,6 @@ void PEI::replaceFrameIndices(MachineBasicBlock *BB, MachineFunction &Fn,
     // Update register states.
     if (RS && !FrameIndexVirtualScavenging && MI) RS->forward(MI);
   }
-
-  // If we have evenly matched pairs of frame setup / destroy instructions,
-  // make sure the adjustments come out to zero. If we don't have matched
-  // pairs, we can't be sure the missing bit isn't in another basic block
-  // due to a custom inserter playing tricks, so just asserting SPAdj==0
-  // isn't sufficient. See tMOVCC on Thumb1, for example.
-  assert((SPAdjCount || SPAdj == 0) &&
-         "Unbalanced call frame setup / destroy pairs?");
 }
 
 /// scavengeFrameVirtualRegs - Replace all frame index virtual registers
-- 
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