Streamline the API of salvageDebugInfoImpl (NFC)

This patch refactors / simplifies salvageDebugInfoImpl(). The goal
here is to simplify the implementation of coro::salvageDebugInfo() in
a followup patch.

  1. Change the return value to I.getOperand(0). Currently users of
     salvageDebugInfoImpl() assume that the first operand is
     I.getOperand(0). This patch makes this information explicit. A
     nice side-effect of this change is that it allows us to salvage
     expressions such as add i8 1, %a in the future.

  2. Factor out the creation of a DIExpression and return an array of
     DIExpression operations instead. This change allows users that
     call salvageDebugInfoImpl() in a loop to avoid the costly
     creation of temporary DIExpressions and to defer the creation of
     a DIExpression until the end.

This patch does not change any functionality.

rdar://80227769

Differential Revision: https://reviews.llvm.org/D107383

1 files changed, 8 insertions, 6 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index e0e4eed..514b215 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -1281,21 +1281,23 @@ void SelectionDAGBuilder::salvageUnresolvedDbgValue(DanglingDebugInfo &DDI) {
   while (isa<Instruction>(V)) {
     Instruction &VAsInst = *cast<Instruction>(V);
     // Temporary "0", awaiting real implementation.
+    SmallVector<uint64_t, 16> Ops;
     SmallVector<Value *, 4> AdditionalValues;
-    DIExpression *SalvagedExpr =
-        salvageDebugInfoImpl(VAsInst, Expr, StackValue, 0, AdditionalValues);
-
+    V = salvageDebugInfoImpl(VAsInst, Expr->getNumLocationOperands(), Ops,
+                             AdditionalValues);
     // If we cannot salvage any further, and haven't yet found a suitable debug
     // expression, bail out.
+    if (!V)
+      break;
+
     // 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())
+    if (!AdditionalValues.empty())
       break;
 
     // New value and expr now represent this debuginfo.
-    V = VAsInst.getOperand(0);
-    Expr = SalvagedExpr;
+    Expr = DIExpression::appendOpsToArg(Expr, Ops, 0, StackValue);
 
     // Some kind of simplification occurred: check whether the operand of the
     // salvaged debug expression can be encoded in this DAG.