Partial Reapply "[DebugInfo] Use variadic debug values to salvage BinOps and GEP instrs with non-const operands"

This is a partial reapply of the original commit and the followup commit
that were previously reverted; this reapply also includes a small fix
for a potential source of non-determinism, but also has a small change
to turn off variadic debug value salvaging, to ensure that any future
revert/reapply steps to disable and renable this feature do not risk
causing conflicts.

Differential Revision: https://reviews.llvm.org/D91722

This reverts commit 386b66b2fc297cda121a3cc8a36887a6ecbcfc68.

1 files changed, 12 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index fd576ea..b63246a 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -1248,6 +1248,10 @@ void SelectionDAGBuilder::resolveDanglingDebugInfo(const Value *V,
 }
 
 void SelectionDAGBuilder::salvageUnresolvedDbgValue(DanglingDebugInfo &DDI) {
+  // TODO: For the variadic implementation, instead of only checking the fail
+  // state of `handleDebugValue`, we need know specifically which values were
+  // invalid, so that we attempt to salvage only those values when processing
+  // a DIArgList.
   assert(!DDI.getDI()->hasArgList() &&
          "Not implemented for variadic dbg_values");
   Value *V = DDI.getDI()->getValue(0);
@@ -1271,16 +1275,21 @@ void SelectionDAGBuilder::salvageUnresolvedDbgValue(DanglingDebugInfo &DDI) {
   while (isa<Instruction>(V)) {
     Instruction &VAsInst = *cast<Instruction>(V);
     // Temporary "0", awaiting real implementation.
-    DIExpression *NewExpr = salvageDebugInfoImpl(VAsInst, Expr, StackValue, 0);
+    SmallVector<Value *, 4> AdditionalValues;
+    DIExpression *SalvagedExpr =
+        salvageDebugInfoImpl(VAsInst, Expr, StackValue, 0, AdditionalValues);
 
     // If we cannot salvage any further, and haven't yet found a suitable debug
     // expression, bail out.
-    if (!NewExpr)
+    // TODO: If AdditionalValues isn't empty, then the salvage can only be
+    // represented with a DBG_VALUE_LIST, so we give up. When we have support
+    // here for variadic dbg_values, remove that condition.
+    if (!SalvagedExpr || !AdditionalValues.empty())
       break;
 
     // New value and expr now represent this debuginfo.
     V = VAsInst.getOperand(0);
-    Expr = NewExpr;
+    Expr = SalvagedExpr;
 
     // Some kind of simplification occurred: check whether the operand of the
     // salvaged debug expression can be encoded in this DAG.