[llvm] [InstrRef] Add debug hint for not reachable blocks from entry (PR #77725)

[via llvm-commits]

https://github.com/HaohaiWen created https://github.com/llvm/llvm-project/pull/77725

Those not reachable blocks was not analyzed by LiveDebugValues and may
raise out of bound access to VarLocs as case in #77441.

>From 09c55464de468ffc37f900289566bf3fe77de857 Mon Sep 17 00:00:00 2001
From: Haohai Wen <haohai.wen at intel.com>
Date: Thu, 11 Jan 2024 12:20:33 +0800
Subject: [PATCH] [InstrRef] Add debug hint for not reachable blocks from entry

Those not reachable blocks was not analyzed by LiveDebugValues and may
raise out of bound access to VarLocs as case in #77441.
---
 llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp b/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp
index 9037f752dc4f36..cfc8c28b99e562 100644
--- a/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp
+++ b/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp
@@ -2403,8 +2403,15 @@ bool InstrRefBasedLDV::mlocJoin(
   llvm::sort(BlockOrders, Cmp);
 
   // Skip entry block.
-  if (BlockOrders.size() == 0)
+  if (BlockOrders.size() == 0) {
+    // FIXME: We don't use assert here to prevent instr-ref-unreachable.mir
+    // failing.
+    LLVM_DEBUG(if (!MBB.isEntryBlock()) dbgs()
+               << "Found not reachable block " << MBB.getFullName()
+               << " from entry which may lead out of "
+                  "bound access to VarLocs\n");
     return false;
+  }
 
   // Step through all machine locations, look at each predecessor and test
   // whether we can eliminate redundant PHIs.