[AArch64] Enable shrink-wrapping by default

[qcolombet]

Summary

Hi,

This is the AArch64 version of enable shrink-wrapping by default, but since copy/paste are cheap, here is a longer description :).

This patch enables shrink-wrapping by default for AArch64.
I have tested shrink-wrapping and no correctness problems came out or runtime regressions.
Although the gain may be small, the code looks nicer with shrink-wrapping enabled and the performance could just be better.

For the record shrink-wrapping was introduced after this review:
http://reviews.llvm.org/D9210

More information on Shrink-Wrapping:
http://lists.llvm.org/pipermail/llvm-dev/2015-May/085220.html

OK to commit?

Thanks,
-Quentin

[mcrosier]

I have no objections to this change. Assuming Tim or others don't object, LGTM.

[qcolombet]

Hi Tim,

What are your thoughts on this patch?

Thanks,
-Quentin

[t.p.northover]

Looks fine to me too.

Tim.

[qcolombet]

r 253520

lib/Target/AArch64/AArch64FrameLowering.h

public:
   /// \brief Can this function use the red zone for local allocations.
   bool canUseRedZone(const MachineFunction &MF) const;
 
   bool hasFP(const MachineFunction &MF) const override;
   bool hasReservedCallFrame(const MachineFunction &MF) const override;
 
   void determineCalleeSaves(MachineFunction &MF, BitVector &SavedRegs,
                             RegScavenger *RS) const override;
+
+  /// Returns true if the target will correctly handle shrink wrapping.
+  bool enableShrinkWrapping(const MachineFunction &MF) const override {
+    return true;
+  }
 };
 
 } // End llvm namespace
 
 #endif

test/CodeGen/AArch64/aarch64-dynamic-stack-layout.ll

bb0:
   br label %bb1
 
 bb1:
   ret void
 }
 
 ; CHECK-LABEL: realign_conditional2
 ; Extra realignment in the prologue (performance issue).
+; CHECK:  tbz  {{.*}} .[[LABEL:.*]]
 ; CHECK:  sub  x9, sp, #32            // =32
 ; CHECK:  and  sp, x9, #0xffffffffffffffe0
 ; CHECK:  mov   x19, sp
-; CHECK:  tbz  {{.*}} .[[LABEL:.*]]
 ; Stack is realigned in a non-entry BB.
 ; CHECK:  sub  [[REG:x[01-9]+]], sp, #64
 ; CHECK:  and  sp, [[REG]], #0xffffffffffffffe0
 ; CHECK:  .[[LABEL]]:
 ; CHECK:  ret
 
 attributes #0 = { "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
 attributes #1 = { nounwind "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
 
 !1 = !{!2, !2, i64 0}
 !2 = !{!"int", !3, i64 0}
 !3 = !{!"omnipotent char", !4, i64 0}
 !4 = !{!"Simple C/C++ TBAA"}