ARM: fold prologue/epilogue sp updates into push/pop for code size

ARM prologues usually look like:
    push {r7, lr}
    sub sp, sp, #4

If code size is extremely important, this can be optimised to the single
instruction:
    push {r6, r7, lr}

where we don't actually care about the contents of r6, but pushing it subtracts
4 from sp as a side effect.

This should implement such a conversion, predicated on the "minsize" function
attribute (-Oz) since I've yet to find any code it actually makes faster.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194264 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 18 insertions, 0 deletions

diff --git a/lib/Target/ARM/ARMBaseInstrInfo.h b/lib/Target/ARM/ARMBaseInstrInfo.h
index 8ab06fd8c2..93e59647d2 100644
--- a/lib/Target/ARM/ARMBaseInstrInfo.h
+++ b/lib/Target/ARM/ARMBaseInstrInfo.h
@@ -362,6 +362,17 @@ bool isIndirectBranchOpcode(int Opc) {
   return Opc == ARM::BX || Opc == ARM::MOVPCRX || Opc == ARM::tBRIND;
 }
 
+static inline bool isPopOpcode(int Opc) {
+  return Opc == ARM::tPOP_RET || Opc == ARM::LDMIA_RET ||
+         Opc == ARM::t2LDMIA_RET || Opc == ARM::tPOP || Opc == ARM::LDMIA_UPD ||
+         Opc == ARM::t2LDMIA_UPD || Opc == ARM::VLDMDIA_UPD;
+}
+
+static inline bool isPushOpcode(int Opc) {
+  return Opc == ARM::tPUSH || Opc == ARM::t2STMDB_UPD ||
+         Opc == ARM::STMDB_UPD || Opc == ARM::VSTMDDB_UPD;
+}
+
 /// getInstrPredicate - If instruction is predicated, returns its predicate
 /// condition, otherwise returns AL. It also returns the condition code
 /// register by reference.
@@ -401,6 +412,13 @@ void emitThumbRegPlusImmediate(MachineBasicBlock &MBB,
                                const ARMBaseRegisterInfo& MRI,
                                unsigned MIFlags = 0);
 
+/// Tries to add registers to the reglist of a given base-updating
+/// push/pop instruction to adjust the stack by an additional
+/// NumBytes. This can save a few bytes per function in code-size, but
+/// obviously generates more memory traffic. As such, it only takes
+/// effect in functions being optimised for size.
+bool tryFoldSPUpdateIntoPushPop(MachineFunction &MF, MachineInstr *MI,
+                                unsigned NumBytes);
 
 /// rewriteARMFrameIndex / rewriteT2FrameIndex -
 /// Rewrite MI to access 'Offset' bytes from the FP. Return false if the