[PATCH] D46232: [SystemZ, IPRA] determineCalleeSaves must always add return register and DP.

[Jonas Paulsson via Phabricator via llvm-commits]

jonpa created this revision.
jonpa added reviewers: uweigand, qcolombet.

When enabling IPRA on SystemZ, a benchmark crashed and I found out that a function had been optimized to not save the Callee Saved Registers, which unfortunately included the return register (%r14) on SystemZ, so when the function tried to return UB resulted.

To fix this, I beleive SystemZFrameLowering::determineCalleeSaves() needs to add R14D to SavedRegs. I also think the DP should be added (https://reviews.llvm.org/source/libunwind/), in case the calling function uses DP, right?

In SystemZFrameLowering::determineCalleeSaves(), the first call to TargetFrameLowering::determineCalleeSaves(MF, SavedRegs, RS) will not add any registers to SavedRegs if

  // When interprocedural register allocation is enabled caller saved registers
  // are preferred over callee saved registers.
  if (MF.getTarget().Options.EnableIPRA && isSafeForNoCSROpt(MF.getFunction()))
    return;

So, the question then is what registers we must save in this case, and which we in fact do not have to save, to get better performance with IPRA. So far, I have come to the conclusion that all the specially treated registers that SystemZFrameLowering::determineCalleeSaves is already adding needs to be saved with IPRA.

I made two tests - one each for https://reviews.llvm.org/source/libunwind/ and R14. For some reason I could not process the debug output without doing a separate run for it.


https://reviews.llvm.org/D46232

Files:
  lib/Target/SystemZ/SystemZFrameLowering.cpp
  test/CodeGen/SystemZ/ipra-02.ll
  test/CodeGen/SystemZ/ipra-03.ll

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