Don't separate imp/expl def handling for call site params

[dstenb]

Summary

Since D70431 the describeLoadedValue() hook takes a parameter register,
meaning that it can now be asked to describe any register. This means
that we can drop the difference between explicit and implicit defines
that we previously had in collectCallSiteParameters().

I have not found any case for any upstream targets where a parameter
register is only implicitly defined, and does not overlap with any
explicit defines. I don't know if such a case would even make sense. So
as far as I have tested, this patch should be a non-functional change.
However, this reduces the complexity of the code a bit, and it will
simplify the implementation of an upcoming patch which solves PR44118.

[djtodoro]

Looks good to me (nit included)!

Thanks for the code clean up!

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

628–632

Perhaps we should add a comment here describing what the FwdRegDefs is used for, or rename the variable.

[djtodoro]

Please wait for someone else from the debug-info project to take a look as well, before committing this.

[dstenb]

Add comment to variable.

[dstenb]

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

628–632

My naming imagination was a bit lackluster, so I added a comment.

[vsk]

Thanks, lgtm.

[djtodoro]

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

628–632

nice, thanks!

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

for (auto ArgReg : CallFwdRegsInfo->second) {
     (void)InsertedReg;
   }
 
   // We erase, from the ForwardedRegWorklist, those forwarding registers for
   // which we successfully describe a loaded value (by using
   // the describeLoadedValue()). For those remaining arguments in the working
   // list, for which we do not describe a loaded value by
   // the describeLoadedValue(), we try to generate an entry value expression
-  // for their call site value desctipion, if the call is within the entry MBB.
+  // for their call site value description, if the call is within the entry MBB.
   // The RegsForEntryValues maps a forwarding register into the register holding
   // the entry value.
   // TODO: Handle situations when call site parameter value can be described
-  // as the entry value within basic blocks other then the first one.
+  // as the entry value within basic blocks other than the first one.
   bool ShouldTryEmitEntryVals = MBB->getIterator() == MF->begin();
   DenseMap<unsigned, unsigned> RegsForEntryValues;
 
   // If the MI is an instruction defining one or more parameters' forwarding
-  // registers, add those defines. We can currently only describe forwarded
-  // registers that are explicitly defined, but keep track of implicit defines
-  // also to remove those registers from the work list.
+  // registers, add those defines.
   auto getForwardingRegsDefinedByMI = [&](const MachineInstr &MI,
-                                          SmallVectorImpl<unsigned> &Explicit,
-                                          SmallVectorImpl<unsigned> &Implicit) {
+                                          SmallSetVector<unsigned, 4> &Defs) {
     if (MI.isDebugInstr())
       return;
 
     for (const MachineOperand &MO : MI.operands()) {
       if (MO.isReg() && MO.isDef() &&
           Register::isPhysicalRegister(MO.getReg())) {
-        for (auto FwdReg : ForwardedRegWorklist) {
-          if (TRI->regsOverlap(FwdReg, MO.getReg())) {
-            if (MO.isImplicit())
-              Implicit.push_back(FwdReg);
-            else
-              Explicit.push_back(FwdReg);
-          }
-        }
+        for (auto FwdReg : ForwardedRegWorklist)
+          if (TRI->regsOverlap(FwdReg, MO.getReg()))
+            Defs.insert(FwdReg);
       }
     }
   };
 
   auto finishCallSiteParam = [&](DbgValueLoc DbgLocVal, unsigned Reg) {
     unsigned FwdReg = Reg;
     if (ShouldTryEmitEntryVals) {
       auto EntryValReg = RegsForEntryValues.find(Reg);
for (; I != MBB->rend(); ++I) {
     // If the next instruction is a call we can not interpret parameter's
     // forwarding registers or we finished the interpretation of all parameters.
     if (I->isCall())
       return;
 
     if (ForwardedRegWorklist.empty())
       return;
 
-    SmallVector<unsigned, 4> ExplicitFwdRegDefs;
-    SmallVector<unsigned, 4> ImplicitFwdRegDefs;
-    getForwardingRegsDefinedByMI(*I, ExplicitFwdRegDefs, ImplicitFwdRegDefs);
-    if (ExplicitFwdRegDefs.empty() && ImplicitFwdRegDefs.empty())
+    // Set of worklist registers that are defined by this instruction.
+    SmallSetVector<unsigned, 4> FwdRegDefs;
+
+    getForwardingRegsDefinedByMI(*I, FwdRegDefs);
+    if (FwdRegDefs.empty())
       continue;
 
     // If the MI clobbers more then one forwarding register we must remove
     // all of them from the working list.
-    for (auto Reg : concat<unsigned>(ExplicitFwdRegDefs, ImplicitFwdRegDefs))
+    for (auto Reg : FwdRegDefs)
       ForwardedRegWorklist.erase(Reg);
 
-    for (auto ParamFwdReg : ExplicitFwdRegDefs) {
+    for (auto ParamFwdReg : FwdRegDefs) {
       if (auto ParamValue = TII->describeLoadedValue(*I, ParamFwdReg)) {
         if (ParamValue->first.isImm()) {
           int64_t Val = ParamValue->first.getImm();
           DbgValueLoc DbgLocVal(ParamValue->second, Val);
           finishCallSiteParam(DbgLocVal, ParamFwdReg);
         } else if (ParamValue->first.isReg()) {
           Register RegLoc = ParamValue->first.getReg();
           // TODO: For now, there is no use of describing the value loaded into the