[llvm] [SystemZ, DebugInfo] Support InstrRef-based Debug Value Tracking in the SystemZ backend (PR #132415)

[Dominik Steenken via llvm-commits]

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@@ -346,6 +346,52 @@ Register SystemZInstrInfo::isStoreToStackSlot(const MachineInstr &MI,
   return isSimpleMove(MI, FrameIndex, SystemZII::SimpleBDXStore);
 }
 
+Register SystemZInstrInfo::isLoadFromStackSlotPostFE(const MachineInstr &MI,
+                                                     int &FrameIndex) const {
+  // if this is not a simple load from memory, it's not a load from stack slot
+  // either.
+  const MCInstrDesc &MCID = MI.getDesc();
+  if (!(MCID.TSFlags & SystemZII::SimpleBDXLoad))
+    return 0;
+
+  Register Reg;
+  // If the frame index is still there, use it.
+  if ((Reg = isLoadFromStackSlot(MI, FrameIndex)))
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dominik-steenken wrote:

I was confused by this as well, but i am still learning the codebase and am taking a lot of cuew from how things are implemented elsewhere, and `X86` does this exact same thing (see [here](https://github.com/llvm/llvm-project/blob/849e5ea94fe8c0007f73ea793ba2a986608a67be/llvm/lib/Target/X86/X86InstrInfo.cpp#L707)). Maybe there are circumstances where this function is called earlier?

https://github.com/llvm/llvm-project/pull/132415