From 0affe0c8cf199d1b00503f5babfa2bebb508329f Mon Sep 17 00:00:00 2001
From: Jay Foad <jay.foad@amd.com>
Date: Fri, 2 Dec 2022 14:07:11 +0000
Subject: [PATCH] Revert "[AMDGPU] Speedup
 GCNDownwardRPTracker::advanceBeforeNext"

This reverts commit 2d09bec169277fb5a341249afacff532c7511756.

It was causing assertion failures in some out-of-tree tests.
---
 llvm/lib/Target/AMDGPU/GCNRegPressure.cpp | 35 +++++++----------------
 1 file changed, 10 insertions(+), 25 deletions(-)

diff --git a/llvm/lib/Target/AMDGPU/GCNRegPressure.cpp b/llvm/lib/Target/AMDGPU/GCNRegPressure.cpp
index 4b055d883e38..f9bed9a76c6f 100644
--- a/llvm/lib/Target/AMDGPU/GCNRegPressure.cpp
+++ b/llvm/lib/Target/AMDGPU/GCNRegPressure.cpp
@@ -336,38 +336,23 @@ bool GCNDownwardRPTracker::advanceBeforeNext() {
   assert(SI.isValid());
 
   // Remove dead registers or mask bits.
-  SmallSet<Register, 8> SeenRegs;
-  for (auto &MO : LastTrackedMI->operands()) {
-    if (!MO.isReg() || !MO.getReg().isVirtual())
-      continue;
-    if (MO.isUse() && !MO.readsReg())
-      continue;
-    if (!SeenRegs.insert(MO.getReg()).second)
-      continue;
-    const LiveInterval &LI = LIS.getInterval(MO.getReg());
+  for (auto &It : LiveRegs) {
+    const LiveInterval &LI = LIS.getInterval(It.first);
     if (LI.hasSubRanges()) {
-      auto It = LiveRegs.end();
       for (const auto &S : LI.subranges()) {
         if (!S.liveAt(SI)) {
-          if (It == LiveRegs.end()) {
-            It = LiveRegs.find(MO.getReg());
-            if (It == LiveRegs.end())
-              llvm_unreachable("register isn't live");
-          }
-          auto PrevMask = It->second;
-          It->second &= ~S.LaneMask;
-          CurPressure.inc(MO.getReg(), PrevMask, It->second, *MRI);
+          auto PrevMask = It.second;
+          It.second &= ~S.LaneMask;
+          CurPressure.inc(It.first, PrevMask, It.second, *MRI);
         }
       }
-      if (It != LiveRegs.end() && It->second.none())
-        LiveRegs.erase(It);
     } else if (!LI.liveAt(SI)) {
-      auto It = LiveRegs.find(MO.getReg());
-      if (It == LiveRegs.end())
-        llvm_unreachable("register isn't live");
-      CurPressure.inc(MO.getReg(), It->second, LaneBitmask::getNone(), *MRI);
-      LiveRegs.erase(It);
+      auto PrevMask = It.second;
+      It.second = LaneBitmask::getNone();
+      CurPressure.inc(It.first, PrevMask, It.second, *MRI);
     }
+    if (It.second.none())
+      LiveRegs.erase(It.first);
   }
 
   MaxPressure = max(MaxPressure, CurPressure);