[llvm] ddfdecb - [MISched] Add statistics to quantify scheduling (#138090)

[via llvm-commits]

Author: Cullen Rhodes
Date: 2025-05-07T07:47:16+01:00
New Revision: ddfdecbd00d2e9ac9b710c33ec9a7a1a6e4498ce

URL: https://github.com/llvm/llvm-project/commit/ddfdecbd00d2e9ac9b710c33ec9a7a1a6e4498ce
DIFF: https://github.com/llvm/llvm-project/commit/ddfdecbd00d2e9ac9b710c33ec9a7a1a6e4498ce.diff

LOG: [MISched] Add statistics to quantify scheduling (#138090)

When diagnosing scheduler issues it can be useful to know how scheduling
changes the order of instructions, particularly for large functions when
it's not trivial to figure out from the debug output by looking at the
scheduling unit (SU) IDs.

This adds pre-RA and post-RA statistics to track 1) the number of
instructions that remain in source order after scheduling and 2) the
total number of instructions scheduled, to compare 1) against.

Added: 
    

Modified: 
    llvm/include/llvm/CodeGen/MachineScheduler.h
    llvm/lib/CodeGen/MachineScheduler.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/include/llvm/CodeGen/MachineScheduler.h b/llvm/include/llvm/CodeGen/MachineScheduler.h
index bc00d0b4ff852..1660fe6864a92 100644
--- a/llvm/include/llvm/CodeGen/MachineScheduler.h
+++ b/llvm/include/llvm/CodeGen/MachineScheduler.h
@@ -1196,6 +1196,9 @@ class GenericSchedulerBase : public MachineSchedStrategy {
   const MachineSchedContext *Context;
   const TargetSchedModel *SchedModel = nullptr;
   const TargetRegisterInfo *TRI = nullptr;
+  unsigned TopIdx = 0;
+  unsigned BotIdx = 0;
+  unsigned NumRegionInstrs = 0;
 
   MachineSchedPolicy RegionPolicy;
 

diff  --git a/llvm/lib/CodeGen/MachineScheduler.cpp b/llvm/lib/CodeGen/MachineScheduler.cpp
index 31acfef45cfee..b8a7eb6b4068b 100644
--- a/llvm/lib/CodeGen/MachineScheduler.cpp
+++ b/llvm/lib/CodeGen/MachineScheduler.cpp
@@ -74,6 +74,14 @@ using namespace llvm;
 
 #define DEBUG_TYPE "machine-scheduler"
 
+STATISTIC(NumInstrsInSourceOrderPreRA,
+          "Number of instructions in source order after pre-RA scheduling");
+STATISTIC(NumInstrsInSourceOrderPostRA,
+          "Number of instructions in source order after post-RA scheduling");
+STATISTIC(NumInstrsScheduledPreRA,
+          "Number of instructions scheduled by pre-RA scheduler");
+STATISTIC(NumInstrsScheduledPostRA,
+          "Number of instructions scheduled by post-RA scheduler");
 STATISTIC(NumClustered, "Number of load/store pairs clustered");
 
 namespace llvm {
@@ -3505,6 +3513,9 @@ void GenericScheduler::initPolicy(MachineBasicBlock::iterator Begin,
     RegionPolicy.OnlyBottomUp = false;
     RegionPolicy.OnlyTopDown = false;
   }
+
+  BotIdx = NumRegionInstrs - 1;
+  this->NumRegionInstrs = NumRegionInstrs;
 }
 
 void GenericScheduler::dumpPolicy() const {
@@ -3981,6 +3992,18 @@ SUnit *GenericScheduler::pickNode(bool &IsTopNode) {
 
   LLVM_DEBUG(dbgs() << "Scheduling SU(" << SU->NodeNum << ") "
                     << *SU->getInstr());
+
+  if (IsTopNode) {
+    if (SU->NodeNum == TopIdx++)
+      ++NumInstrsInSourceOrderPreRA;
+  } else {
+    assert(BotIdx < NumRegionInstrs && "out of bounds");
+    if (SU->NodeNum == BotIdx--)
+      ++NumInstrsInSourceOrderPreRA;
+  }
+
+  NumInstrsScheduledPreRA += 1;
+
   return SU;
 }
 
@@ -4104,6 +4127,9 @@ void PostGenericScheduler::initPolicy(MachineBasicBlock::iterator Begin,
     RegionPolicy.OnlyBottomUp = false;
     RegionPolicy.OnlyTopDown = false;
   }
+
+  BotIdx = NumRegionInstrs - 1;
+  this->NumRegionInstrs = NumRegionInstrs;
 }
 
 void PostGenericScheduler::registerRoots() {
@@ -4323,6 +4349,18 @@ SUnit *PostGenericScheduler::pickNode(bool &IsTopNode) {
 
   LLVM_DEBUG(dbgs() << "Scheduling SU(" << SU->NodeNum << ") "
                     << *SU->getInstr());
+
+  if (IsTopNode) {
+    if (SU->NodeNum == TopIdx++)
+      ++NumInstrsInSourceOrderPostRA;
+  } else {
+    assert(BotIdx < NumRegionInstrs && "out of bounds");
+    if (SU->NodeNum == BotIdx--)
+      ++NumInstrsInSourceOrderPostRA;
+  }
+
+  NumInstrsScheduledPostRA += 1;
+
   return SU;
 }