[llvm] [CodeGen] Correctly handle non-standard cases in RemoveLoadsIntoFakeUses (PR #111551)

[Jeremy Morse via llvm-commits]

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@@ -74,6 +77,10 @@ INITIALIZE_PASS_END(RemoveLoadsIntoFakeUses, DEBUG_TYPE,
                     "Remove Loads Into Fake Uses", false, false)
 
 bool RemoveLoadsIntoFakeUses::runOnMachineFunction(MachineFunction &MF) {
+  // Skip this pass if we would use VarLoc-based LDV, as there may be DBG_VALUE
+  // instructions of the restored values that would become invalid.
+  if (debuginfoShouldUseDebugInstrRef(MF.getTarget().getTargetTriple()))
+    return false;
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jmorse wrote:

I believe instead this should be using the "UseDebugInstrRef" field of MachineFunction -- observe the `MachineFunction::shouldUseDebugInstrRef` function, there are compositions of attributes and flags that mess up instruction referencing, thus it's enabled on a function-by-function basis.

Sad to say, but that'll mean we need a test too.

https://github.com/llvm/llvm-project/pull/111551