[llvm] [TargetParser][AArch64] Believe runtime feature detection (PR #95694)

[via llvm-commits]

https://github.com/workingjubilee updated https://github.com/llvm/llvm-project/pull/95694

>From 56265e59e6729990ec3984c897999b5417b70ceb Mon Sep 17 00:00:00 2001
From: Jubilee Young <workingjubilee at gmail.com>
Date: Sun, 16 Jun 2024 01:59:59 -0700
Subject: [PATCH 1/2] [TargetParser][AArch64] Believe runtime feature detection

---
 llvm/lib/TargetParser/Host.cpp | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/llvm/lib/TargetParser/Host.cpp b/llvm/lib/TargetParser/Host.cpp
index 2ea56746aff24..0cb0419746459 100644
--- a/llvm/lib/TargetParser/Host.cpp
+++ b/llvm/lib/TargetParser/Host.cpp
@@ -1967,21 +1967,23 @@ bool sys::getHostCPUFeatures(StringMap<bool> &Features) {
   }
 
 #if defined(__aarch64__)
-  // If we have all crypto bits we can add the feature
-  if (crypto == (CAP_AES | CAP_PMULL | CAP_SHA1 | CAP_SHA2))
-    Features["crypto"] = true;
+  // LLVM has decided some AArch64 CPUs have all the instructions they _may_
+  // have, as opposed to all the instructions they _must_ have, so allow runtime
+  // information to correct us on that.
+  Features["crypto"] = (crypto == (CAP_AES | CAP_PMULL | CAP_SHA1 | CAP_SHA2));
 #endif
 
   return true;
 }
 #elif defined(_WIN32) && (defined(__aarch64__) || defined(_M_ARM64))
 bool sys::getHostCPUFeatures(StringMap<bool> &Features) {
-  if (IsProcessorFeaturePresent(PF_ARM_NEON_INSTRUCTIONS_AVAILABLE))
-    Features["neon"] = true;
-  if (IsProcessorFeaturePresent(PF_ARM_V8_CRC32_INSTRUCTIONS_AVAILABLE))
-    Features["crc"] = true;
-  if (IsProcessorFeaturePresent(PF_ARM_V8_CRYPTO_INSTRUCTIONS_AVAILABLE))
-    Features["crypto"] = true;
+  // If we're asking the OS at runtime, believe what the OS says
+  Features["neon"] =
+      IsProcessorFeaturePresent(PF_ARM_NEON_INSTRUCTIONS_AVAILABLE);
+  Features["crc"] =
+      IsProcessorFeaturePresent(PF_ARM_V8_CRC32_INSTRUCTIONS_AVAILABLE);
+  Features["crypto"] =
+      IsProcessorFeaturePresent(PF_ARM_V8_CRYPTO_INSTRUCTIONS_AVAILABLE);
 
   return true;
 }

>From 6c9e72d33a31910c226e2733f4e5a8b7096c157e Mon Sep 17 00:00:00 2001
From: Jubilee Young <workingjubilee at gmail.com>
Date: Mon, 17 Jun 2024 11:24:40 -0700
Subject: [PATCH 2/2] [TargetParser][AArch64] Split crypto feature detection
 into AES & SHA2

---
 llvm/lib/TargetParser/Host.cpp | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/llvm/lib/TargetParser/Host.cpp b/llvm/lib/TargetParser/Host.cpp
index 0cb0419746459..5f3fda18772fa 100644
--- a/llvm/lib/TargetParser/Host.cpp
+++ b/llvm/lib/TargetParser/Host.cpp
@@ -1924,7 +1924,8 @@ bool sys::getHostCPUFeatures(StringMap<bool> &Features) {
     }
 
 #if defined(__aarch64__)
-  // Keep track of which crypto features we have seen
+  // All of these are "crypto" features, but we must sift out actual features
+  // as the former meaning of "crypto" as a single feature is no more.
   enum { CAP_AES = 0x1, CAP_PMULL = 0x2, CAP_SHA1 = 0x4, CAP_SHA2 = 0x8 };
   uint32_t crypto = 0;
 #endif
@@ -1970,7 +1971,10 @@ bool sys::getHostCPUFeatures(StringMap<bool> &Features) {
   // LLVM has decided some AArch64 CPUs have all the instructions they _may_
   // have, as opposed to all the instructions they _must_ have, so allow runtime
   // information to correct us on that.
-  Features["crypto"] = (crypto == (CAP_AES | CAP_PMULL | CAP_SHA1 | CAP_SHA2));
+  uint32_t aes = CAP_AES | CAP_PMULL;
+  uint32_t sha2 = CAP_SHA1 | CAP_SHA2;
+  Features["aes"] = (crypto & aes) == aes;
+  Features["sha2"] = (crypto & sha2) == sha2;
 #endif
 
   return true;
@@ -1982,8 +1986,12 @@ bool sys::getHostCPUFeatures(StringMap<bool> &Features) {
       IsProcessorFeaturePresent(PF_ARM_NEON_INSTRUCTIONS_AVAILABLE);
   Features["crc"] =
       IsProcessorFeaturePresent(PF_ARM_V8_CRC32_INSTRUCTIONS_AVAILABLE);
-  Features["crypto"] =
+
+  // Avoid inferring "crypto" means more than the traditional AES + SHA2
+  bool trad_crypto =
       IsProcessorFeaturePresent(PF_ARM_V8_CRYPTO_INSTRUCTIONS_AVAILABLE);
+  Features["aes"] = crypto;
+  Features["sha2"] = crypto;
 
   return true;
 }