[llvm-commits] [llvm] r72898 - /llvm/trunk/lib/Target/X86/X86RegisterInfo.cpp

[Bill Wendling]

Author: void
Date: Thu Jun  4 17:52:30 2009
New Revision: 72898

URL: http://llvm.org/viewvc/llvm-project?rev=72898&view=rev
Log:
The DWARF unwind info was incorrect. While compiling with
`-fomit-frame-pointer', we would lack the DW_CFA_advance_loc information for a
lot of function, and then they would be `0'. The linker (at least on Darwin)
needs to encode the stack size. In some cases, the stack size is too large to
directly encode. So the linker checks to see if there is a "subl $xxx,%esp"
instruction at the point where the `DW_CFA_def_cfa_offset' says the pc was. If
so, the compact encoding records the offset in the function to where the stack
size is embedded. But because the `DW_CFA_advance_loc' instructions are missing,
it looks before the function and dies.

So, instead of emitting the EH debug label before the stack adjustment
operations, emit it afterwards, right before the frame move stuff.

Modified:
    llvm/trunk/lib/Target/X86/X86RegisterInfo.cpp

Modified: llvm/trunk/lib/Target/X86/X86RegisterInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86RegisterInfo.cpp?rev=72898&r1=72897&r2=72898&view=diff

==============================================================================
--- llvm/trunk/lib/Target/X86/X86RegisterInfo.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86RegisterInfo.cpp Thu Jun  4 17:52:30 2009
@@ -822,13 +822,6 @@
     NumBytes = StackSize - X86FI->getCalleeSavedFrameSize();
   }
 
-  unsigned ReadyLabelId = 0;
-  if (needsFrameMoves) {
-    // Mark effective beginning of when frame pointer is ready.
-    ReadyLabelId = MMI->NextLabelID();
-    BuildMI(MBB, MBBI, DL, TII.get(X86::DBG_LABEL)).addImm(ReadyLabelId);
-  }
-
   // Skip the callee-saved push instructions.
   while (MBBI != MBB.end() &&
          (MBBI->getOpcode() == X86::PUSH32r ||
@@ -838,20 +831,20 @@
   if (MBBI != MBB.end())
     DL = MBBI->getDebugLoc();
 
-  if (NumBytes) {   // adjust stack pointer: ESP -= numbytes
+  if (NumBytes) {   // Adjust stack pointer: ESP -= numbytes.
     if (NumBytes >= 4096 && Subtarget->isTargetCygMing()) {
-      // Check, whether EAX is livein for this function
+      // Check, whether EAX is livein for this function.
       bool isEAXAlive = false;
       for (MachineRegisterInfo::livein_iterator
            II = MF.getRegInfo().livein_begin(),
            EE = MF.getRegInfo().livein_end(); (II != EE) && !isEAXAlive; ++II) {
         unsigned Reg = II->first;
         isEAXAlive = (Reg == X86::EAX || Reg == X86::AX ||
-                      Reg == X86::AH || Reg == X86::AL);
+                      Reg == X86::AH  || Reg == X86::AL);
       }
 
-      // Function prologue calls _alloca to probe the stack when allocating
-      // more than 4k bytes in one go. Touching the stack at 4K increments is
+      // Function prologue calls _alloca to probe the stack when allocating more
+      // than 4k bytes in one go. Touching the stack at 4K increments is
       // necessary to ensure that the guard pages used by the OS virtual memory
       // manager are allocated in correct sequence.
       if (!isEAXAlive) {
@@ -863,12 +856,14 @@
         // Save EAX
         BuildMI(MBB, MBBI, DL, TII.get(X86::PUSH32r))
           .addReg(X86::EAX, RegState::Kill);
+
         // Allocate NumBytes-4 bytes on stack. We'll also use 4 already
         // allocated bytes for EAX.
-        BuildMI(MBB, MBBI, DL, 
-                TII.get(X86::MOV32ri), X86::EAX).addImm(NumBytes-4);
+        BuildMI(MBB, MBBI, DL, TII.get(X86::MOV32ri), X86::EAX)
+          .addImm(NumBytes-4);
         BuildMI(MBB, MBBI, DL, TII.get(X86::CALLpcrel32))
           .addExternalSymbol("_alloca");
+
         // Restore EAX
         MachineInstr *MI = addRegOffset(BuildMI(MF, DL, TII.get(X86::MOV32rm),
                                                 X86::EAX),
@@ -880,6 +875,7 @@
       // merge the two. This can be the case when tail call elimination is
       // enabled and the callee has more arguments then the caller.
       NumBytes -= mergeSPUpdates(MBB, MBBI, StackPtr, true);
+
       // If there is an ADD32ri or SUB32ri of ESP immediately after this
       // instruction, merge the two instructions.
       mergeSPUpdatesDown(MBB, MBBI, StackPtr, &NumBytes);
@@ -889,8 +885,13 @@
     }
   }
 
-  if (needsFrameMoves)
+  if (needsFrameMoves) {
+    // Mark effective beginning of when frame pointer is ready.
+    unsigned ReadyLabelId = 0;
+    ReadyLabelId = MMI->NextLabelID();
+    BuildMI(MBB, MBBI, DL, TII.get(X86::DBG_LABEL)).addImm(ReadyLabelId);
     emitFrameMoves(MF, FrameLabelId, ReadyLabelId);
+  }
 }
 
 void X86RegisterInfo::emitEpilogue(MachineFunction &MF,