From 061ec365a8850d140aa5069fc7d2a4c380be4752 Mon Sep 17 00:00:00 2001
From: JosJuice <josjuice@gmail.com>
Date: Fri, 9 Jun 2023 19:21:57 +0200
Subject: [PATCH] PPCAnalyst: Reduce number of iterations in
 ReorderInstructionsCore

We can utilize the fact that if swapping two instructions causes another
swap to become possible, that swap involves one of the two instructions
we just swapped. There's need to search for new swap opportunities as
far back as the beginning of the block; we can just go one step back.
---
 Source/Core/Core/PowerPC/PPCAnalyst.cpp | 92 +++++++++++++++----------
 1 file changed, 57 insertions(+), 35 deletions(-)

diff --git a/Source/Core/Core/PowerPC/PPCAnalyst.cpp b/Source/Core/Core/PowerPC/PPCAnalyst.cpp
index 34501a5bbe..8e6a1eee00 100644
--- a/Source/Core/Core/PowerPC/PPCAnalyst.cpp
+++ b/Source/Core/Core/PowerPC/PPCAnalyst.cpp
@@ -470,52 +470,74 @@ static bool isCror(const CodeOp& a)
 void PPCAnalyzer::ReorderInstructionsCore(u32 instructions, CodeOp* code, bool reverse,
                                           ReorderType type) const
 {
-  // Bubbling an instruction sometimes reveals another opportunity to bubble an instruction, so do
-  // multiple passes.
+  // Instruction Reordering Pass
+  // Carry pass: bubble carry-using instructions as close to each other as possible, so we can avoid
+  // storing the carry flag.
+  // Compare pass: bubble compare instructions next to branches, so they can be merged.
+
+  const int start = reverse ? instructions - 1 : 0;
+  const int end = reverse ? 0 : instructions - 1;
+  const int increment = reverse ? -1 : 1;
+
+  int i = start;
+  int next = start;
+  bool go_backwards = false;
+
   while (true)
   {
-    // Instruction Reordering Pass
-    // Carry pass: bubble carry-using instructions as close to each other as possible, so we can
-    // avoid
-    // storing the carry flag.
-    // Compare pass: bubble compare instructions next to branches, so they can be merged.
-    bool swapped = false;
-    int increment = reverse ? -1 : 1;
-    int start = reverse ? instructions - 1 : 0;
-    int end = reverse ? 0 : instructions - 1;
-    for (int i = start; i != end; i += increment)
+    if (go_backwards)
     {
-      CodeOp& a = code[i];
-      CodeOp& b = code[i + increment];
-      // Reorder integer compares, rlwinm., and carry-affecting ops
-      // (if we add more merged branch instructions, add them here!)
-      if ((type == ReorderType::CROR && isCror(a)) ||
-          (type == ReorderType::Carry && isCarryOp(a)) ||
-          (type == ReorderType::CMP && (isCmp(a) || a.outputCR[0])))
+      i -= increment;
+      go_backwards = false;
+    }
+    else
+    {
+      i = next;
+      next += increment;
+    }
+
+    if (i == end)
+      break;
+
+    CodeOp& a = code[i];
+    CodeOp& b = code[i + increment];
+
+    // Reorder integer compares, rlwinm., and carry-affecting ops
+    // (if we add more merged branch instructions, add them here!)
+    if ((type == ReorderType::CROR && isCror(a)) || (type == ReorderType::Carry && isCarryOp(a)) ||
+        (type == ReorderType::CMP && (isCmp(a) || a.outputCR[0])))
+    {
+      // once we're next to a carry instruction, don't move away!
+      if (type == ReorderType::Carry && i != start)
       {
-        // once we're next to a carry instruction, don't move away!
-        if (type == ReorderType::Carry && i != start)
+        // if we read the CA flag, and the previous instruction sets it, don't move away.
+        if (!reverse && (a.opinfo->flags & FL_READ_CA) &&
+            (code[i - increment].opinfo->flags & FL_SET_CA))
         {
-          // if we read the CA flag, and the previous instruction sets it, don't move away.
-          if (!reverse && (a.opinfo->flags & FL_READ_CA) &&
-              (code[i - increment].opinfo->flags & FL_SET_CA))
-            continue;
-          // if we set the CA flag, and the next instruction reads it, don't move away.
-          if (reverse && (a.opinfo->flags & FL_SET_CA) &&
-              (code[i - increment].opinfo->flags & FL_READ_CA))
-            continue;
+          continue;
         }
 
-        if (CanSwapAdjacentOps(a, b))
+        // if we set the CA flag, and the next instruction reads it, don't move away.
+        if (reverse && (a.opinfo->flags & FL_SET_CA) &&
+            (code[i - increment].opinfo->flags & FL_READ_CA))
         {
-          // Alright, let's bubble it!
-          std::swap(a, b);
-          swapped = true;
+          continue;
+        }
+      }
+
+      if (CanSwapAdjacentOps(a, b))
+      {
+        // Alright, let's bubble it!
+        std::swap(a, b);
+
+        if (i != start)
+        {
+          // Bubbling an instruction sometimes reveals another opportunity to bubble an instruction,
+          // so go one step backwards and check if we have such an opportunity.
+          go_backwards = true;
         }
       }
     }
-    if (!swapped)
-      return;
   }
 }