[llvm] 8ea5eac - [MISched] Fix off-by-one error in debug output with -misched-cutoff=<n> flag (#137988)

[via llvm-commits]

Author: Cullen Rhodes
Date: 2025-05-06T11:12:23+01:00
New Revision: 8ea5eacea263ed5c2c4b0950a4d1d6ef863444bc

URL: https://github.com/llvm/llvm-project/commit/8ea5eacea263ed5c2c4b0950a4d1d6ef863444bc
DIFF: https://github.com/llvm/llvm-project/commit/8ea5eacea263ed5c2c4b0950a4d1d6ef863444bc.diff

LOG: [MISched] Fix off-by-one error in debug output with -misched-cutoff=<n> flag (#137988)

This flag instructs the scheduler to stop scheduling after N
instructions, but
in the debug output it appears as if it's scheduling N+1 instructions,
e.g.

$ llc -misched-cutoff=10 -debug-only=machine-scheduler
example.ll 2>&1 | grep "^Scheduling SU" | wc -l
11

as it calls pickNode before calling checkSchedLimit.

Added: 
    

Modified: 
    llvm/lib/CodeGen/MachineScheduler.cpp
    llvm/test/CodeGen/AArch64/misched-cutoff.mir

Removed: 
    


################################################################################
diff  --git a/llvm/lib/CodeGen/MachineScheduler.cpp b/llvm/lib/CodeGen/MachineScheduler.cpp
index 0c3ffb1bbaa6f..31acfef45cfee 100644
--- a/llvm/lib/CodeGen/MachineScheduler.cpp
+++ b/llvm/lib/CodeGen/MachineScheduler.cpp
@@ -1003,13 +1003,14 @@ void ScheduleDAGMI::schedule() {
 
   bool IsTopNode = false;
   while (true) {
+    if (!checkSchedLimit())
+      break;
+
     LLVM_DEBUG(dbgs() << "** ScheduleDAGMI::schedule picking next node\n");
     SUnit *SU = SchedImpl->pickNode(IsTopNode);
     if (!SU) break;
 
     assert(!SU->isScheduled && "Node already scheduled");
-    if (!checkSchedLimit())
-      break;
 
     MachineInstr *MI = SU->getInstr();
     if (IsTopNode) {
@@ -1637,13 +1638,14 @@ void ScheduleDAGMILive::schedule() {
 
   bool IsTopNode = false;
   while (true) {
+    if (!checkSchedLimit())
+      break;
+
     LLVM_DEBUG(dbgs() << "** ScheduleDAGMILive::schedule picking next node\n");
     SUnit *SU = SchedImpl->pickNode(IsTopNode);
     if (!SU) break;
 
     assert(!SU->isScheduled && "Node already scheduled");
-    if (!checkSchedLimit())
-      break;
 
     scheduleMI(SU, IsTopNode);
 

diff  --git a/llvm/test/CodeGen/AArch64/misched-cutoff.mir b/llvm/test/CodeGen/AArch64/misched-cutoff.mir
index a81fe1102ac9f..a61eb64318a39 100644
--- a/llvm/test/CodeGen/AArch64/misched-cutoff.mir
+++ b/llvm/test/CodeGen/AArch64/misched-cutoff.mir
@@ -4,7 +4,7 @@
 
 # REQUIRES: asserts
 
-# CHECK-CUTOFF-COUNT-2: Scheduling SU
+# CHECK-CUTOFF-COUNT-1: Scheduling SU
 
 # NOTE: copied from machine-scheduler.mir