[llvm] [AMDGPU][SIInsertWaitcnts] don't crash when printing messages at end of block (PR #145694)

[Sameer Sahasrabuddhe via llvm-commits]

https://github.com/ssahasra created https://github.com/llvm/llvm-project/pull/145694

None

>From 760b8ee98c0e166f892c0edb9b7f4fc6ea29b9c8 Mon Sep 17 00:00:00 2001
From: Sameer Sahasrabuddhe <sameer.sahasrabuddhe at amd.com>
Date: Wed, 25 Jun 2025 18:19:39 +0530
Subject: [PATCH] [AMDGPU][SIInsertWaitcnts] don't crash when printing messages
 at end of block

---
 llvm/lib/Target/AMDGPU/SIInsertWaitcnts.cpp | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/Target/AMDGPU/SIInsertWaitcnts.cpp b/llvm/lib/Target/AMDGPU/SIInsertWaitcnts.cpp
index f43831016952a..98e1696056f11 100644
--- a/llvm/lib/Target/AMDGPU/SIInsertWaitcnts.cpp
+++ b/llvm/lib/Target/AMDGPU/SIInsertWaitcnts.cpp
@@ -1353,7 +1353,14 @@ bool WaitcntGeneratorPreGFX12::applyPreexistingWaitcnt(
   MachineInstr *WaitcntInstr = nullptr;
   MachineInstr *WaitcntVsCntInstr = nullptr;
 
-  LLVM_DEBUG(dbgs() << "PreGFX12::applyPreexistingWaitcnt at: " << *It);
+  // clang-format off
+  LLVM_DEBUG(dbgs() << "PreGFX12::applyPreexistingWaitcnt at: ";
+             if (It == OldWaitcntInstr.getParent()->instr_end())
+               dbgs() << "end of block\n";
+             else
+               dbgs() << *It;
+             );
+  // clang-format on
 
   for (auto &II :
        make_early_inc_range(make_range(OldWaitcntInstr.getIterator(), It))) {
@@ -1377,6 +1384,7 @@ bool WaitcntGeneratorPreGFX12::applyPreexistingWaitcnt(
 
       // Merge consecutive waitcnt of the same type by erasing multiples.
       if (WaitcntInstr || (!Wait.hasWaitExceptStoreCnt() && TrySimplify)) {
+        LLVM_DEBUG(dbgs() << "erased waitcnt: " << II);
         II.eraseFromParent();
         Modified = true;
       } else
@@ -1507,7 +1515,10 @@ bool WaitcntGeneratorGFX12Plus::applyPreexistingWaitcnt(
   MachineInstr *CombinedStoreDsCntInstr = nullptr;
   MachineInstr *WaitInstrs[NUM_EXTENDED_INST_CNTS] = {};
 
-  LLVM_DEBUG(dbgs() << "GFX12Plus::applyPreexistingWaitcnt at: " << *It);
+  LLVM_DEBUG(dbgs() << "GFX12Plus::applyPreexistingWaitcnt at: ";
+             if (It == OldWaitcntInstr.getParent()->instr_end()) dbgs()
+             << "end of block\n";
+             else dbgs() << *It);
 
   for (auto &II :
        make_early_inc_range(make_range(OldWaitcntInstr.getIterator(), It))) {