[llvm-commits] CVS: llvm/lib/Target/ARM/ARMRegisterInfo.cpp ARMRegisterInfo.h

[Evan Cheng]

Changes in directory llvm/lib/Target/ARM:

ARMRegisterInfo.cpp updated: 1.90 -> 1.91
ARMRegisterInfo.h updated: 1.17 -> 1.18
---
Log message:

Under normal circumstances, when a frame pointer is not required, we reserve
argument space for call sites in the function immediately on entry to the
current function. This eliminates the need for add/sub sp brackets around call
sites. However, this is not always a good idea. If the "call frame" is large and
the target load / store instructions have small immediate field to encode sp
offset, this can cause poor codegen. In the worst case, this can make it
impossible to scavenge a register if the reserved spill slot is pushed too far
apart from sp / fp.

---
Diffs of the changes:  (+29 -3)

 ARMRegisterInfo.cpp |   30 +++++++++++++++++++++++++++---
 ARMRegisterInfo.h   |    2 ++
 2 files changed, 29 insertions(+), 3 deletions(-)


Index: llvm/lib/Target/ARM/ARMRegisterInfo.cpp
diff -u llvm/lib/Target/ARM/ARMRegisterInfo.cpp:1.90 llvm/lib/Target/ARM/ARMRegisterInfo.cpp:1.91
--- llvm/lib/Target/ARM/ARMRegisterInfo.cpp:1.90	Fri Apr 27 15:10:08 2007
+++ llvm/lib/Target/ARM/ARMRegisterInfo.cpp	Mon Apr 30 19:52:08 2007
@@ -386,6 +386,29 @@
   return NoFramePointerElim || MF.getFrameInfo()->hasVarSizedObjects();
 }
 
+// hasReservedCallFrame - Under normal circumstances, when a frame pointer is
+// not required, we reserve argument space for call sites in the function
+// immediately on entry to the current function. This eliminates the need for
+// add/sub sp brackets around call sites. Returns true if the call frame is
+// included as part of the stack frame.
+bool ARMRegisterInfo::hasReservedCallFrame(MachineFunction &MF) const {
+  const MachineFrameInfo *FFI = MF.getFrameInfo();
+  unsigned CFSize = FFI->getMaxCallFrameSize();
+  ARMFunctionInfo *AFI = MF.getInfo<ARMFunctionInfo>();
+  // It's not always a good idea to include the call frame as part of the
+  // stack frame. ARM (especially Thumb) has small immediate offset to
+  // address the stack frame. So a large call frame can cause poor codegen
+  // and may even makes it impossible to scavenge a register.
+  if (AFI->isThumbFunction()) {
+    if (CFSize >= ((1 << 8) - 1) * 4 / 2) // Half of imm8 * 4
+      return false;
+  } else {
+    if (CFSize >= ((1 << 12) - 1) / 2)  // Half of imm12
+      return false;
+  }
+  return !hasFP(MF);
+}
+
 /// emitARMRegPlusImmediate - Emits a series of instructions to materialize
 /// a destreg = basereg + immediate in ARM code.
 static
@@ -605,7 +628,7 @@
 void ARMRegisterInfo::
 eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
                               MachineBasicBlock::iterator I) const {
-  if (hasFP(MF)) {
+  if (!hasReservedCallFrame(MF)) {
     // If we have alloca, convert as follows:
     // ADJCALLSTACKDOWN -> sub, sp, sp, amount
     // ADJCALLSTACKUP   -> add, sp, sp, amount
@@ -1146,8 +1169,9 @@
                 Limit = (1 << 8) - 1;
                 goto DoneEstimating;
               } else if (AddrMode == ARMII::AddrMode5) {
-                Limit = ((1 << 8) - 1) * 4;
-                goto DoneEstimating;
+                unsigned ThisLimit = ((1 << 8) - 1) * 4;
+                if (ThisLimit < Limit)
+                  Limit = ThisLimit;
               }
             }
         }


Index: llvm/lib/Target/ARM/ARMRegisterInfo.h
diff -u llvm/lib/Target/ARM/ARMRegisterInfo.h:1.17 llvm/lib/Target/ARM/ARMRegisterInfo.h:1.18
--- llvm/lib/Target/ARM/ARMRegisterInfo.h:1.17	Tue Mar 20 03:07:04 2007
+++ llvm/lib/Target/ARM/ARMRegisterInfo.h	Mon Apr 30 19:52:08 2007
@@ -78,6 +78,8 @@
 
   bool hasFP(const MachineFunction &MF) const;
 
+  bool hasReservedCallFrame(MachineFunction &MF) const;
+
   void eliminateCallFramePseudoInstr(MachineFunction &MF,
                                      MachineBasicBlock &MBB,
                                      MachineBasicBlock::iterator I) const;