From 23c844b2aa84a65e573dcc023d19b8f5294a8baf Mon Sep 17 00:00:00 2001
From: jhorv <38920027+jhorv@users.noreply.github.com>
Date: Sat, 11 Mar 2023 15:05:48 -0500
Subject: Misc performance tweaks (#4509)

* use Array.Empty() where instead of allocating new zero-length arrays

* structure for loops in a way that the JIT will elide array/Span bounds checking

* avoiding function calls in for loop condition tests

* avoid LINQ in a hot path

* conform with code style

* fix mistake in GetNextWaitingObject()

* fix GetNextWaitingObject() possibility of returning null if all list items have TimePoint == long.MaxValue

* make GetNextWaitingObject() behave FIFO behavior for multiple items with the same TimePoint
---
 ARMeilleure/CodeGen/Arm64/CodeGenContext.cs                   | 2 +-
 ARMeilleure/CodeGen/RegisterAllocators/LinearScanAllocator.cs | 9 ++-------
 ARMeilleure/Decoders/DecoderHelper.cs                         | 4 ++--
 ARMeilleure/Decoders/OpCodeTable.cs                           | 6 +++---
 4 files changed, 8 insertions(+), 13 deletions(-)

(limited to 'ARMeilleure')

diff --git a/ARMeilleure/CodeGen/Arm64/CodeGenContext.cs b/ARMeilleure/CodeGen/Arm64/CodeGenContext.cs
index 1ddde0c1..cebfbde1 100644
--- a/ARMeilleure/CodeGen/Arm64/CodeGenContext.cs
+++ b/ARMeilleure/CodeGen/Arm64/CodeGenContext.cs
@@ -265,7 +265,7 @@ namespace ARMeilleure.CodeGen.Arm64
             }
             else
             {
-                relocInfo = new RelocInfo(new RelocEntry[0]);
+                relocInfo = new RelocInfo(Array.Empty<RelocEntry>());
             }
 
             return (code, relocInfo);
diff --git a/ARMeilleure/CodeGen/RegisterAllocators/LinearScanAllocator.cs b/ARMeilleure/CodeGen/RegisterAllocators/LinearScanAllocator.cs
index 6ea62c28..d80157af 100644
--- a/ARMeilleure/CodeGen/RegisterAllocators/LinearScanAllocator.cs
+++ b/ARMeilleure/CodeGen/RegisterAllocators/LinearScanAllocator.cs
@@ -433,16 +433,11 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
 
         private static int GetHighestValueIndex(Span<int> span)
         {
-            int highest = span[0];
-
-            if (highest == int.MaxValue)
-            {
-                return 0;
-            }
+            int highest = int.MinValue;
 
             int selected = 0;
 
-            for (int index = 1; index < span.Length; index++)
+            for (int index = 0; index < span.Length; index++)
             {
                 int current = span[index];
 
diff --git a/ARMeilleure/Decoders/DecoderHelper.cs b/ARMeilleure/Decoders/DecoderHelper.cs
index 38f98c39..5227e6a1 100644
--- a/ARMeilleure/Decoders/DecoderHelper.cs
+++ b/ARMeilleure/Decoders/DecoderHelper.cs
@@ -17,7 +17,7 @@ namespace ARMeilleure.Decoders
         {
             uint[] tbl = new uint[256];
 
-            for (int idx = 0; idx < 256; idx++)
+            for (int idx = 0; idx < tbl.Length; idx++)
             {
                 tbl[idx] = ExpandImm8ToFP32((uint)idx);
             }
@@ -29,7 +29,7 @@ namespace ARMeilleure.Decoders
         {
             ulong[] tbl = new ulong[256];
 
-            for (int idx = 0; idx < 256; idx++)
+            for (int idx = 0; idx < tbl.Length; idx++)
             {
                 tbl[idx] = ExpandImm8ToFP64((ulong)idx);
             }
diff --git a/ARMeilleure/Decoders/OpCodeTable.cs b/ARMeilleure/Decoders/OpCodeTable.cs
index 54abb141..8464ce55 100644
--- a/ARMeilleure/Decoders/OpCodeTable.cs
+++ b/ARMeilleure/Decoders/OpCodeTable.cs
@@ -1301,7 +1301,7 @@ namespace ARMeilleure.Decoders
         {
             List<InstInfo>[] temp = new List<InstInfo>[FastLookupSize];
 
-            for (int index = 0; index < FastLookupSize; index++)
+            for (int index = 0; index < temp.Length; index++)
             {
                 temp[index] = new List<InstInfo>();
             }
@@ -1311,7 +1311,7 @@ namespace ARMeilleure.Decoders
                 int mask  = ToFastLookupIndex(inst.Mask);
                 int value = ToFastLookupIndex(inst.Value);
 
-                for (int index = 0; index < FastLookupSize; index++)
+                for (int index = 0; index < temp.Length; index++)
                 {
                     if ((index & mask) == value)
                     {
@@ -1320,7 +1320,7 @@ namespace ARMeilleure.Decoders
                 }
             }
 
-            for (int index = 0; index < FastLookupSize; index++)
+            for (int index = 0; index < temp.Length; index++)
             {
                 table[index] = temp[index].ToArray();
             }
-- 
cgit v1.2.3