[PATCH] D89451: [SystemZ] Mark unsaved argument R6 as live throughout function

Thu Oct 15 15:54:03 PDT 2020

efriedma added a comment.

This seems like the right approach.  It feels weird, but I can't think of anything better.

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Comment at: llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp:356
+  if (MF.front().isLiveIn(SystemZ::R6D) && LowGPR &&
+      SystemZMC::getFirstReg(LowGPR) > SystemZMC::getFirstReg(SystemZ::R6D)) {
+    // Clear any kill flags.
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Not sure I understand what the `LowGPR && SystemZMC::getFirstReg(LowGPR) > SystemZMC::getFirstReg(SystemZ::R6D)` is doing.  We should be checking whether the register was spilled in the prologue.

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Comment at: llvm/test/CodeGen/SystemZ/frame-26.ll:6
+; Test that R6 when used for an argument is modelled as being live throughout
+; the function when not saved in the prologue..
+
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Probably want an MIR testcase; smaller, and more likely to continue to hit the case in question in the future.

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D89451/new/

https://reviews.llvm.org/D89451