[llvm] [CodeGen] Preserved additional analyses in StackSlotColoring pass. (PR #93779)

[Vikash Gupta via llvm-commits]

https://github.com/vg0204 updated https://github.com/llvm/llvm-project/pull/93779

>From dc214360217a58d6b7b6a05f773bea348a62c496 Mon Sep 17 00:00:00 2001
From: vg0204 <Vikash.Gupta at amd.com>
Date: Thu, 30 May 2024 13:00:08 +0530
Subject: [PATCH 1/4] [CodeGen] Preserved additional analyses in
 StackSlotColoring pass.

The pass pipeline of some architecture splits register allocation
phase based on different register classes. As some analyses need to
be computed at the beginning of the register allocation and kept
alive till all values are assigned to some physical registers.

This poses challenge with objective of introducing StackSlotColoring
after partial virtual registers are assigned to physical registers,
in order to optimize stack slots usage.As this pass doesn't preserve
few analysis yet to be needed by the register allocation of the
remaining virtual registers, necessiating them to be kept preserved.
---
 llvm/lib/CodeGen/StackSlotColoring.cpp | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/CodeGen/StackSlotColoring.cpp b/llvm/lib/CodeGen/StackSlotColoring.cpp
index 9fdc8a338b52a..0ab6349c4f714 100644
--- a/llvm/lib/CodeGen/StackSlotColoring.cpp
+++ b/llvm/lib/CodeGen/StackSlotColoring.cpp
@@ -13,6 +13,7 @@
 #include "llvm/ADT/BitVector.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Statistic.h"
+#include "llvm/CodeGen/LiveDebugVariables.h"
 #include "llvm/CodeGen/LiveInterval.h"
 #include "llvm/CodeGen/LiveIntervalUnion.h"
 #include "llvm/CodeGen/LiveIntervals.h"
@@ -64,6 +65,7 @@ namespace {
     MachineFrameInfo *MFI = nullptr;
     const TargetInstrInfo *TII = nullptr;
     const MachineBlockFrequencyInfo *MBFI = nullptr;
+    SlotIndexes *Indexes = nullptr;
 
     // SSIntervals - Spill slot intervals.
     std::vector<LiveInterval*> SSIntervals;
@@ -152,6 +154,14 @@ namespace {
       AU.addRequired<MachineBlockFrequencyInfo>();
       AU.addPreserved<MachineBlockFrequencyInfo>();
       AU.addPreservedID(MachineDominatorsID);
+
+      // As in some Target's pipeline, register allocation (RA) might be
+      // splitted into multiple phases based on register class. So, this pass
+      // may be invoked multiple times requiring it to save these analyses to be
+      // used by RA later.
+      AU.addPreserved<LiveIntervals>();
+      AU.addPreserved<LiveDebugVariables>();
+
       MachineFunctionPass::getAnalysisUsage(AU);
     }
 
@@ -496,8 +506,10 @@ bool StackSlotColoring::RemoveDeadStores(MachineBasicBlock* MBB) {
     ++I;
   }
 
-  for (MachineInstr *MI : toErase)
+  for (MachineInstr *MI : toErase) {
     MI->eraseFromParent();
+    Indexes->removeMachineInstrFromMaps(*MI);
+  }
 
   return changed;
 }
@@ -515,6 +527,7 @@ bool StackSlotColoring::runOnMachineFunction(MachineFunction &MF) {
   TII = MF.getSubtarget().getInstrInfo();
   LS = &getAnalysis<LiveStacks>();
   MBFI = &getAnalysis<MachineBlockFrequencyInfo>();
+  Indexes = &getAnalysis<SlotIndexes>();
 
   bool Changed = false;
 

>From c8079d776bffb749954262b9791f6a99e3ad817f Mon Sep 17 00:00:00 2001
From: vg0204 <Vikash.Gupta at amd.com>
Date: Mon, 3 Jun 2024 12:17:33 +0530
Subject: [PATCH 2/4] Add recommended changes addressing the grammatical issue
 with comments.

---
 llvm/lib/CodeGen/StackSlotColoring.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/CodeGen/StackSlotColoring.cpp b/llvm/lib/CodeGen/StackSlotColoring.cpp
index 0ab6349c4f714..eb7d730e236bf 100644
--- a/llvm/lib/CodeGen/StackSlotColoring.cpp
+++ b/llvm/lib/CodeGen/StackSlotColoring.cpp
@@ -155,8 +155,8 @@ namespace {
       AU.addPreserved<MachineBlockFrequencyInfo>();
       AU.addPreservedID(MachineDominatorsID);
 
-      // As in some Target's pipeline, register allocation (RA) might be
-      // splitted into multiple phases based on register class. So, this pass
+      // In some Target's pipeline, register allocation (RA) might be
+      // split into multiple phases based on register class. So, this pass
       // may be invoked multiple times requiring it to save these analyses to be
       // used by RA later.
       AU.addPreserved<LiveIntervals>();

>From c56007db74d0d737d013f8e6eb428696caa5762d Mon Sep 17 00:00:00 2001
From: vg0204 <Vikash.Gupta at amd.com>
Date: Fri, 7 Jun 2024 14:54:19 +0530
Subject: [PATCH 3/4] Addressed requested changes after review in
 StackSlotColoring.cpp.

---
 llvm/lib/CodeGen/StackSlotColoring.cpp | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/CodeGen/StackSlotColoring.cpp b/llvm/lib/CodeGen/StackSlotColoring.cpp
index eb7d730e236bf..f4daf7f912df6 100644
--- a/llvm/lib/CodeGen/StackSlotColoring.cpp
+++ b/llvm/lib/CodeGen/StackSlotColoring.cpp
@@ -507,8 +507,10 @@ bool StackSlotColoring::RemoveDeadStores(MachineBasicBlock* MBB) {
   }
 
   for (MachineInstr *MI : toErase) {
+    if (Indexes) {
+      Indexes->removeMachineInstrFromMaps(*MI);
+    }
     MI->eraseFromParent();
-    Indexes->removeMachineInstrFromMaps(*MI);
   }
 
   return changed;

>From eb410b852197e6b823a5c6822bc70c8b443c9048 Mon Sep 17 00:00:00 2001
From: vg0204 <Vikash.Gupta at amd.com>
Date: Mon, 10 Jun 2024 22:00:53 +0530
Subject: [PATCH 4/4] Removed unnecessary braces from stackSlotColoring.cpp

---
 llvm/lib/CodeGen/StackSlotColoring.cpp | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/llvm/lib/CodeGen/StackSlotColoring.cpp b/llvm/lib/CodeGen/StackSlotColoring.cpp
index f4daf7f912df6..eb7a113b575f7 100644
--- a/llvm/lib/CodeGen/StackSlotColoring.cpp
+++ b/llvm/lib/CodeGen/StackSlotColoring.cpp
@@ -507,9 +507,8 @@ bool StackSlotColoring::RemoveDeadStores(MachineBasicBlock* MBB) {
   }
 
   for (MachineInstr *MI : toErase) {
-    if (Indexes) {
+    if (Indexes)
       Indexes->removeMachineInstrFromMaps(*MI);
-    }
     MI->eraseFromParent();
   }