[llvm] [AArch64] Make compiling arm_neon.h faster (PR #226378)

[Nico Weber via llvm-commits]

https://github.com/nico updated https://github.com/llvm/llvm-project/pull/226378

>From 01f3018d9d21412f44be5357e4b5fe7f793baf52 Mon Sep 17 00:00:00 2001
From: Nico Weber <thakis at chromium.org>
Date: Sun, 20 Sep 2026 12:40:26 -0400
Subject: [PATCH 1/2] [AArch64] Make compiling arm_neon.h faster
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Replace two linear scans with map lookups.

On my system, reduces time to compile a TU that does nothing but
`#include <arm_neon.h>` from 92.0 ms ± 1.4 ms to 70.9 ms ± 1.3 ms.

No behavior change.
---
 llvm/lib/TargetParser/AArch64TargetParser.cpp | 28 +++++++++++++------
 1 file changed, 20 insertions(+), 8 deletions(-)

diff --git a/llvm/lib/TargetParser/AArch64TargetParser.cpp b/llvm/lib/TargetParser/AArch64TargetParser.cpp
index b7ceb0bb403c30..ee0a5204c1429c 100644
--- a/llvm/lib/TargetParser/AArch64TargetParser.cpp
+++ b/llvm/lib/TargetParser/AArch64TargetParser.cpp
@@ -12,6 +12,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/TargetParser/AArch64TargetParser.h"
+#include "llvm/ADT/StringMap.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/Format.h"
 #include "llvm/Support/raw_ostream.h"
@@ -165,10 +166,15 @@ std::optional<AArch64::ExtensionInfo>
 AArch64::parseArchExtension(StringRef ArchExt) {
   if (ArchExt.empty())
     return {};
-  for (const auto &A : Extensions) {
-    if (ArchExt == StrTab[A.UserVisibleName] || ArchExt == StrTab[A.Alias])
-      return A;
-  }
+  static const StringMap<const ExtensionInfo *> NameToExtension = [] {
+    StringMap<const ExtensionInfo *> Map;
+    for (const auto &A : Extensions)
+      for (StringRef Name : {StrTab[A.UserVisibleName], StrTab[A.Alias]})
+        Map.try_emplace(Name, &A);
+    return Map;
+  }();
+  if (const ExtensionInfo *A = NameToExtension.lookup(ArchExt))
+    return *A;
   return {};
 }
 
@@ -186,10 +192,16 @@ std::optional<AArch64::FMVInfo> AArch64::parseFMVExtension(StringRef FMVExt) {
 
 std::optional<AArch64::ExtensionInfo>
 AArch64::targetFeatureToExtension(StringRef TargetFeature) {
-  for (const auto &E : Extensions)
-    if (TargetFeature == StrTab[E.PosTargetFeature] ||
-        TargetFeature == StrTab[E.NegTargetFeature])
-      return E;
+  static const StringMap<const ExtensionInfo *> FeatureToExtension = [] {
+    StringMap<const ExtensionInfo *> Map;
+    for (const auto &E : Extensions)
+      for (StringRef Feature :
+           {StrTab[E.PosTargetFeature], StrTab[E.NegTargetFeature]})
+        Map.try_emplace(Feature, &E);
+    return Map;
+  }();
+  if (const ExtensionInfo *E = FeatureToExtension.lookup(TargetFeature))
+    return *E;
   return {};
 }
 

>From 0707215e3163abb35ca4cde4af8f7500c1700e37 Mon Sep 17 00:00:00 2001
From: Nico Weber <thakis at chromium.org>
Date: Fri, 25 Sep 2026 06:06:43 -0700
Subject: [PATCH 2/2] densemap

---
 llvm/lib/TargetParser/AArch64TargetParser.cpp | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/llvm/lib/TargetParser/AArch64TargetParser.cpp b/llvm/lib/TargetParser/AArch64TargetParser.cpp
index ee0a5204c1429c..3624b04ffb81e9 100644
--- a/llvm/lib/TargetParser/AArch64TargetParser.cpp
+++ b/llvm/lib/TargetParser/AArch64TargetParser.cpp
@@ -12,7 +12,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/TargetParser/AArch64TargetParser.h"
-#include "llvm/ADT/StringMap.h"
+#include "llvm/ADT/DenseMap.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/Format.h"
 #include "llvm/Support/raw_ostream.h"
@@ -166,14 +166,14 @@ std::optional<AArch64::ExtensionInfo>
 AArch64::parseArchExtension(StringRef ArchExt) {
   if (ArchExt.empty())
     return {};
-  static const StringMap<const ExtensionInfo *> NameToExtension = [] {
-    StringMap<const ExtensionInfo *> Map;
+  static const DenseMap<StringRef, const ExtensionInfo *> NameToExt = [] {
+    DenseMap<StringRef, const ExtensionInfo *> Map;
     for (const auto &A : Extensions)
       for (StringRef Name : {StrTab[A.UserVisibleName], StrTab[A.Alias]})
         Map.try_emplace(Name, &A);
     return Map;
   }();
-  if (const ExtensionInfo *A = NameToExtension.lookup(ArchExt))
+  if (const ExtensionInfo *A = NameToExt.lookup(ArchExt))
     return *A;
   return {};
 }
@@ -192,15 +192,15 @@ std::optional<AArch64::FMVInfo> AArch64::parseFMVExtension(StringRef FMVExt) {
 
 std::optional<AArch64::ExtensionInfo>
 AArch64::targetFeatureToExtension(StringRef TargetFeature) {
-  static const StringMap<const ExtensionInfo *> FeatureToExtension = [] {
-    StringMap<const ExtensionInfo *> Map;
+  static const DenseMap<StringRef, const ExtensionInfo *> FeatureToExt = [] {
+    DenseMap<StringRef, const ExtensionInfo *> Map;
     for (const auto &E : Extensions)
       for (StringRef Feature :
            {StrTab[E.PosTargetFeature], StrTab[E.NegTargetFeature]})
         Map.try_emplace(Feature, &E);
     return Map;
   }();
-  if (const ExtensionInfo *E = FeatureToExtension.lookup(TargetFeature))
+  if (const ExtensionInfo *E = FeatureToExt.lookup(TargetFeature))
     return *E;
   return {};
 }