[llvm-branch-commits] [llvm] [AMDGPU] Skip non-first termintors when forcing emit zero flag (PR #112116)

[Shilei Tian via llvm-branch-commits]

https://github.com/shiltian created https://github.com/llvm/llvm-project/pull/112116

None

>From 59007297616ea2e11a06401b79833953318d42e0 Mon Sep 17 00:00:00 2001
From: Shilei Tian <shilei.tian at amd.com>
Date: Sat, 12 Oct 2024 23:58:25 -0400
Subject: [PATCH] [AMDGPU] Skip non-first termintors when forcing emit zero
 flag

---
 llvm/lib/Target/AMDGPU/SIInsertWaitcnts.cpp   | 15 ++++++++++++-
 .../waitcnt-debug-non-first-terminators.mir   | 22 +++++++++++++++++++
 2 files changed, 36 insertions(+), 1 deletion(-)
 create mode 100644 llvm/test/CodeGen/AMDGPU/waitcnt-debug-non-first-terminators.mir

diff --git a/llvm/lib/Target/AMDGPU/SIInsertWaitcnts.cpp b/llvm/lib/Target/AMDGPU/SIInsertWaitcnts.cpp
index 9866ecbdddb608..28e26dc47b0ab4 100644
--- a/llvm/lib/Target/AMDGPU/SIInsertWaitcnts.cpp
+++ b/llvm/lib/Target/AMDGPU/SIInsertWaitcnts.cpp
@@ -1600,6 +1600,17 @@ static bool callWaitsOnFunctionReturn(const MachineInstr &MI) {
   return true;
 }
 
+/// \returns true if \p MI is not the first terminator of its associated MBB.
+static bool checkIfMBBNonFirstTerminator(const MachineInstr &MI) {
+  const auto &MBB = MI.getParent();
+  if (MBB->getFirstTerminator() == MI)
+    return false;
+  for (const auto &I : MBB->terminators())
+    if (&I == &MI)
+      return true;
+  return false;
+}
+
 ///  Generate s_waitcnt instruction to be placed before cur_Inst.
 ///  Instructions of a given type are returned in order,
 ///  but instructions of different types can complete out of order.
@@ -1825,7 +1836,9 @@ bool SIInsertWaitcnts::generateWaitcntInstBefore(MachineInstr &MI,
   // Verify that the wait is actually needed.
   ScoreBrackets.simplifyWaitcnt(Wait);
 
-  if (ForceEmitZeroFlag)
+  // When forcing emit, we need to skip non-first terminators of a MBB because
+  // that would break the terminators of the MBB.
+  if (ForceEmitZeroFlag && !checkIfMBBNonFirstTerminator(MI))
     Wait = WCG->getAllZeroWaitcnt(/*IncludeVSCnt=*/false);
 
   if (ForceEmitWaitcnt[LOAD_CNT])
diff --git a/llvm/test/CodeGen/AMDGPU/waitcnt-debug-non-first-terminators.mir b/llvm/test/CodeGen/AMDGPU/waitcnt-debug-non-first-terminators.mir
new file mode 100644
index 00000000000000..530d1981f053e9
--- /dev/null
+++ b/llvm/test/CodeGen/AMDGPU/waitcnt-debug-non-first-terminators.mir
@@ -0,0 +1,22 @@
+# RUN: llc -mtriple=amdgcn-amd-amdhsa -run-pass si-insert-waitcnts -amdgpu-waitcnt-forcezero=1 %s -o - | FileCheck %s
+
+...
+
+# CHECK-LABEL: waitcnt-debug-non-first-terminators
+# CHECK: S_WAITCNT 0
+# CHECK-NEXT: S_CBRANCH_SCC1 %bb.1, implicit $scc
+# CHECK-NEXT: S_BRANCH %bb.2, implicit $scc
+
+name: waitcnt-debug-non-first-terminators
+liveins:
+machineFunctionInfo:
+  isEntryFunction: true
+body:             |
+  bb.0:
+    S_CBRANCH_SCC1 %bb.1, implicit $scc
+    S_BRANCH %bb.2, implicit $scc
+  bb.1:
+    S_NOP 0
+  bb.2:
+    S_NOP 0
+...