[X86] Convert esp-relative movs of function arguments to pushes, step 2

This moves the transformation introduced in r223757 into a separate MI pass.
This allows it to cover many more cases (not only cases where there must be a 
reserved call frame), and perform rudimentary call folding. It still doesn't 
have a heuristic, so it is enabled only for optsize/minsize, with stack 
alignment <= 8, where it ought to be a fairly clear win.

(Re-commit of r227728)

Differential Revision: http://reviews.llvm.org/D6789

llvm-svn: 227752

1 files changed, 12 insertions, 8 deletions

diff --git a/llvm/lib/CodeGen/PrologEpilogInserter.cpp b/llvm/lib/CodeGen/PrologEpilogInserter.cpp
index 385e5a3..61407fa 100644
--- a/llvm/lib/CodeGen/PrologEpilogInserter.cpp
+++ b/llvm/lib/CodeGen/PrologEpilogInserter.cpp
@@ -703,7 +703,8 @@ void PEI::insertPrologEpilogCode(MachineFunction &Fn) {
 /// register references and actual offsets.
 ///
 void PEI::replaceFrameIndices(MachineFunction &Fn) {
-  if (!Fn.getFrameInfo()->hasStackObjects()) return; // Nothing to do?
+  const TargetFrameLowering &TFI = *Fn.getSubtarget().getFrameLowering();
+  if (!TFI.needsFrameIndexResolution(Fn)) return;
 
   // Store SPAdj at exit of a basic block.
   SmallVector<int, 8> SPState;
@@ -769,13 +770,6 @@ 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) {
@@ -854,6 +848,16 @@ void PEI::replaceFrameIndices(MachineBasicBlock *BB, MachineFunction &Fn,
       break;
     }
 
+    // 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.
+    // Note that this must come after eliminateFrameIndex, because 
+    // if I itself referred to a frame index, we shouldn't count its own
+    // adjustment.
+    if (MI && InsideCallSequence)
+      SPAdj += TII.getSPAdjust(MI);
+
     if (DoIncr && I != BB->end()) ++I;
 
     // Update register states.