Erase constant dbgloc on reuse in PHI node

Basic block selection involves checking successor BBs for PHI nodes
that depend on the current BB.  In case such BBs are found, the value
being selected is a constant and such constant already exists in
current BB, it's value is reused.

This might lead to wrong locations in some situations, especially if
same constant value ends up being materialized twice in two different
ways, which discards that sharing and leaves us with wrong debug
location in the successor BB.

In code this involves the following sequence of calls:

 SelectionDAGBuilder::HandlePHINodesInSuccessorBlocks ->
 SelectionDAGBuilder::CopyValueToVirtualRegister ->
 SelectionDAGBuilder::getNonRegisterValue

llvm-svn: 239089

1 files changed, 10 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index a0eea9ffb06..cf0900f59e8 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -1002,7 +1002,16 @@ bool SelectionDAGBuilder::findValue(const Value *V) const {
 SDValue SelectionDAGBuilder::getNonRegisterValue(const Value *V) {
   // If we already have an SDValue for this value, use it.
   SDValue &N = NodeMap[V];
-  if (N.getNode()) return N;
+  if (N.getNode()) {
+    if (isa<ConstantSDNode>(N) || isa<ConstantFPSDNode>(N)) {
+      // Remove the debug location from the node as the node is about to be used
+      // in a location which may differ from the original debug location.  This
+      // is relevant to Constant and ConstantFP nodes because they can appear
+      // as constant expressions inside PHI nodes.
+      N->setDebugLoc(DebugLoc());
+    }
+    return N;
+  }
 
   // Otherwise create a new SDValue and remember it.
   SDValue Val = getValueImpl(V);