[X86] Restore X86 base pointer after call to llvm.eh.sjlj.setjmp

Commit on 

- This patch fixes the bug described in
  http://lists.cs.uiuc.edu/pipermail/llvmdev/2013-May/062343.html

The fix allocates an extra slot just below the GPRs and stores the base pointer
there. This is done only for functions containing llvm.eh.sjlj.setjmp that also
need a base pointer. Because code containing llvm.eh.sjlj.setjmp saves all of
the callee-save GPRs in the prologue, the offset to the extra slot can be
computed before prologue generation runs.

Impact at run-time on affected functions is::

  - One extra store in the prologue, The store saves the base pointer.
  - One extra load after a llvm.eh.sjlj.setjmp. The load restores the base pointer.

Because the extra slot is just above a gap between frame-pointer-relative and
base-pointer-relative chunks of memory, there is no impact on other offset
calculations other than ensuring there is room for the extra slot.

http://reviews.llvm.org/D6388

Patch by Arch Robison <arch.robison@intel.com>

llvm-svn: 223329

1 files changed, 13 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/X86FrameLowering.cpp b/llvm/lib/Target/X86/X86FrameLowering.cpp
index f8ada8db292..b6e2d932d81 100644
--- a/llvm/lib/Target/X86/X86FrameLowering.cpp
+++ b/llvm/lib/Target/X86/X86FrameLowering.cpp
@@ -448,6 +448,8 @@ void X86FrameLowering::getStackProbeFunction(const X86Subtarget &STI,
 
   [if needs base pointer]
       mov  %rsp, %rbx
+      [if needs to restore base pointer]
+          mov %rsp, -MMM(%rbp)
 
   ; Emit CFI info
   [if needs FP]
@@ -570,6 +572,9 @@ void X86FrameLowering::emitPrologue(MachineFunction &MF) const {
   if (HasFP) {
     // Calculate required stack adjustment.
     uint64_t FrameSize = StackSize - SlotSize;
+    // If required, include space for extra hidden slot for stashing base pointer.
+    if (X86FI->getRestoreBasePointer()) 
+      FrameSize += SlotSize;
     if (RegInfo->needsStackRealignment(MF)) {
       // Callee-saved registers are pushed on stack before the stack
       // is realigned.
@@ -838,6 +843,14 @@ void X86FrameLowering::emitPrologue(MachineFunction &MF) const {
     BuildMI(MBB, MBBI, DL, TII.get(Opc), BasePtr)
       .addReg(StackPtr)
       .setMIFlag(MachineInstr::FrameSetup);
+    if (X86FI->getRestoreBasePointer()) {
+      // Stash value of base pointer.  Saving RSP instead of EBP shortens dependence chain.
+      unsigned Opm = Uses64BitFramePtr ? X86::MOV64mr : X86::MOV32mr;
+      addRegOffset(BuildMI(MBB, MBBI, DL, TII.get(Opm)),
+                   FramePtr, true, X86FI->getRestoreBasePointerOffset())
+        .addReg(StackPtr)
+        .setMIFlag(MachineInstr::FrameSetup);
+    }
   }
 
   if (((!HasFP && NumBytes) || PushedRegs) && NeedsDwarfCFI) {