[llvm] [llvm-reduce] Fix incorrectly ignored null MD in ReduceDIMetadata (PR #108541)

[Stephen Tozer via llvm-commits]

https://github.com/SLTozer created https://github.com/llvm/llvm-project/pull/108541

Commit c2e62c7 updated the ReduceDIMetadata pass to be able to remove DIGlobalVariableExpressions from MDNode operands; it also accidentally prevented null operands from being preserved, which results in an assertion being triggered:
`Targets == NoChunksCounter.count() && "number of chunks changes when reducing"'

This patch allows us to correctly preserve null operands once again. I've not got a test case for this yet - I'm hoping this patch is just trivially correct as-is, because I've not got the hang of reducing a test case for llvm-reduce yet, but I can get a test case generated if needed.

>From 1fabbdbf4edf569d173cd3a2ce56df6c0054c308 Mon Sep 17 00:00:00 2001
From: Stephen Tozer <stephen.tozer at sony.com>
Date: Fri, 13 Sep 2024 12:39:00 +0100
Subject: [PATCH] [llvm-reduce] Fix incorrectly ignored null MD in
 ReduceDIMetadata

Commit c2e62c7 updated the ReduceDIMetadata pass to be able to remove
DIGlobalVariableExpressions from MDNode operands; it also accidentally
prevented null operands from being preserved, which results in an
assertion being triggered:
`Targets == NoChunksCounter.count() && "number of chunks changes when reducing"'

This patch allows us to correctly preserve null operands once again.
---
 llvm/tools/llvm-reduce/deltas/ReduceDIMetadata.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/llvm/tools/llvm-reduce/deltas/ReduceDIMetadata.cpp b/llvm/tools/llvm-reduce/deltas/ReduceDIMetadata.cpp
index 38352d6342d4f9..fbad6f697584ee 100644
--- a/llvm/tools/llvm-reduce/deltas/ReduceDIMetadata.cpp
+++ b/llvm/tools/llvm-reduce/deltas/ReduceDIMetadata.cpp
@@ -70,8 +70,8 @@ void identifyUninterestingMDNodes(Oracle &O, MDNodeList &MDs) {
           // Don't add uninteresting operands to the tuple.
           if (!O.shouldKeep())
             continue;
-        TN.push_back(Op);
       }
+      TN.push_back(Tup->getOperand(I));
     }
     if (TN.size() != Tup->getNumOperands())
       DbgNode->replaceOperandWith(OpIdx, DbgNode->get(DbgNode->getContext(), TN));