[DebugInfo] Add helper for finding entry value candidates [NFC]

[dstenb]

Summary

The conditions that are used to determine if entry values should be
emitted for a parameter are quite many, and will grow slightly
in a follow-up commit, so move those to a helper function, as was
suggested in the code review for D69889.

[probinson]

Please remember to provide full-context diffs.

llvm/lib/CodeGen/LiveDebugValues.cpp

1304

Not clear why a lambda is better than a static function. The [&] captures way more than you need, for one thing. The only values it uses are MI (already passed as a parameter) and DebugEntryVals.

[djtodoro]

Thanks! This looks good to me, with minor nits inlined.

llvm/lib/CodeGen/LiveDebugValues.cpp

1304

Yes, If we are using lambdas, it is better to use an explicit capture instead of the default capture.

[dstenb]

Move the helper to a separate function rather than a lambda. Include full diff context.

[dstenb]

In D69955#1737420, @probinson wrote:

Please remember to provide full-context diffs.

Yes, sorry about that!

llvm/lib/CodeGen/LiveDebugValues.cpp

95

Taken from D68209.

[djtodoro]

This looks very good to me! Thanks!

llvm/lib/CodeGen/LiveDebugValues.cpp

95

This is OK. I will rebase the diff on top of this one.

1355

One if with the &&?

[dstenb]

Merge if statements.

[djtodoro]

lgtm, thanks!

llvm/lib/CodeGen/LiveDebugValues.cpp

                       std::greater<unsigned int>>
       Pending;
 
-  // Besides parameter's modification, check whether a DBG_VALUE is inlined
-  // in order to deduce whether the variable that it tracks comes from
-  // a different function. If that is the case we can't track its entry value.
-  auto IsUnmodifiedFuncParam = [&](const MachineInstr &MI) {
-    auto *DIVar = MI.getDebugVariable();
-    return DIVar->isParameter() && DIVar->isNotModified() &&
-           !MI.getDebugLoc()->getInlinedAt();
-  };
-
   const TargetLowering *TLI = MF.getSubtarget().getTargetLowering();
   unsigned SP = TLI->getStackPointerRegisterToSaveRestore();
   Register FP = TRI->getFrameRegister(MF);

   // representing candidates for production of debug entry values.
   DebugParamMap DebugEntryVals;
 
-  MachineBasicBlock &First_MBB = *(MF.begin());
   // Only in the case of entry MBB collect DBG_VALUEs representing
   // function parameters in order to generate debug entry values for them.
+  //
   // Currently, we generate debug entry values only for parameters that are
   // unmodified throughout the function and located in a register.
-  // TODO: Add support for parameters that are described as fragments.
-  // TODO: Add support for modified arguments that can be expressed
-  // by using its entry value.
-  // TODO: Add support for local variables that are expressed in terms of
-  // parameters entry values.
+  auto IsEntryValueCandidate = [&](const MachineInstr &MI) {
+    if (!MI.isDebugValue())
+      return false;
+
+    // TODO: Add support for local variables that are expressed in terms of
+    // parameters entry values.
+    // TODO: Add support for modified arguments that can be expressed
+    // by using its entry value.
+    auto *DIVar = MI.getDebugVariable();
+    if (!DIVar->isParameter() || !DIVar->isNotModified())
+      return false;
+
+    // Do not consider parameters that belong to an inlined function.
+    if (MI.getDebugLoc()->getInlinedAt())
+      return false;
+
+    // Do not consider indirect debug values (TODO: explain why).
+    if (MI.isIndirectDebugValue())
+      return false;
+
+    // Only consider parameters that are described using registers. Parameters
+    // that are passed on the stack are not yet supported, so ignore debug
+    // values that are described by the frame or stack pointer.
+    if (!IsRegOtherThanSPAndFP(MI.getOperand(0)))
+      return false;
+
+    // Do not consider parameters that we have already handled.
+    if (DebugEntryVals.count(MI.getDebugVariable()))
+      return false;
+
+    // TODO: Add support for parameters that are described as fragments.
+    if (MI.getDebugExpression()->isFragment())
+      return false;
+
+    return true;
+  };
+
+  MachineBasicBlock &First_MBB = *(MF.begin());
   for (auto &MI : First_MBB)
-    if (MI.isDebugValue() && IsUnmodifiedFuncParam(MI) &&
-        !MI.isIndirectDebugValue() && IsRegOtherThanSPAndFP(MI.getOperand(0)) &&
-        !DebugEntryVals.count(MI.getDebugVariable()) &&
-        !MI.getDebugExpression()->isFragment())
+    if (IsEntryValueCandidate(MI))
       DebugEntryVals[MI.getDebugVariable()] = &MI;
 
   // Initialize per-block structures and scan for fragment overlaps.