[DebugInfo][DAG] Limit special-casing of dbg.values for Arguments

SelectionDAGBuilder has special handling for dbg.value intrinsics that are
understood to define the location of function parameters on entry to the
function. To enable this, we avoid recording a dbg.value as a virtual register
reference if it might be such a parameter, so that it later hits
EmitFuncArgumentDbgValue.

This patch reduces the set of circumstances where we avoid recording a
dbg.value as a virtual register reference, to allow more "normal" variables
to be recorded that way. We now only bypass for potential parameters if:
 * The dbg.value operand is an Argument,
 * The Variable is a parameter, and
 * The Variable is not inlined.
meaning it's very likely that the dbg.value is a function-entry parameter
location.

Differential Revision: https://reviews.llvm.org/D57584

llvm-svn: 353948

1 files changed, 10 insertions, 4 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index a5b43bc0a8e..042a0c3a473 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -5492,10 +5492,16 @@ SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I, unsigned Intrinsic) {
       return nullptr;
     }
 
-    // The value is not used in this block yet (or it would have an SDNode).
-    // We still want the value to appear for the user if possible -- if it has
-    // an associated VReg, we can refer to that instead.
-    if (!isa<Argument>(V)) {
+    // Special rules apply for the first dbg.values of parameter variables in a
+    // function. Identify them by the fact they reference Argument Values, that
+    // they're parameters, and they are parameters of the current function. We
+    // need to let them dangle until they get an SDNode.
+    bool IsParamOfFunc = isa<Argument>(V) && Variable->isParameter() &&
+                         !DI.getDebugLoc()->getInlinedAt();
+    if (!IsParamOfFunc) {
+      // The value is not used in this block yet (or it would have an SDNode).
+      // We still want the value to appear for the user if possible -- if it has
+      // an associated VReg, we can refer to that instead.
       auto VMI = FuncInfo.ValueMap.find(V);
       if (VMI != FuncInfo.ValueMap.end()) {
         unsigned Reg = VMI->second;