[PATCH] D137423: [PowerPC] make expensive mflr be away from its user in the function prologue

[ChenZheng via Phabricator via llvm-commits]

shchenz marked an inline comment as done.
shchenz added inline comments.


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Comment at: llvm/lib/Target/PowerPC/PPCFrameLowering.cpp:621
+  // expensive. We need to consider the latency when backup lr in the prologue.
+  const bool IsCheapMFLR = Subtarget.isISA3_1();
+
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RolandF wrote:
> The cost of an mflr is a characteristic of an implementation, not of the architecture.  A future processor might have a slow mflr.  I think a new subtarget feature is needed for this.
I added a new patch https://reviews.llvm.org/D137612 to add the subtarget feature. Seems for P10, the latency for mflr is only 2 cycles, so I only set the new feature for P10.


Repository:
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CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D137423/new/

https://reviews.llvm.org/D137423