[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 fcd62f65d28978bbea3440014e4bbb0e09efc8b2 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 616e4eda1dd29d..e323e2eb6ade5b 100644
--- a/llvm/lib/TargetParser/Host.cpp
+++ b/llvm/lib/TargetParser/Host.cpp
@@ -1941,9 +1941,10 @@ const StringMap<bool> sys::getHostCPUFeatures() {
   }
 
 #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 Features;
@@ -1952,12 +1953,13 @@ const StringMap<bool> sys::getHostCPUFeatures() {
 const StringMap<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 Features;
 }

>From 0d9373cbc3fa5baaa006003299baf75bd0e2582d 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 e323e2eb6ade5b..14567af8590e63 100644
--- a/llvm/lib/TargetParser/Host.cpp
+++ b/llvm/lib/TargetParser/Host.cpp
@@ -1898,7 +1898,8 @@ const StringMap<bool> sys::getHostCPUFeatures() {
     }
 
 #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
@@ -1944,7 +1945,10 @@ const StringMap<bool> sys::getHostCPUFeatures() {
   // 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 Features;
@@ -1958,8 +1962,12 @@ const StringMap<bool> sys::getHostCPUFeatures() {
       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 TradCrypto =
       IsProcessorFeaturePresent(PF_ARM_V8_CRYPTO_INSTRUCTIONS_AVAILABLE);
+  Features["aes"] = TradCrypto;
+  Features["sha2"] = TradCrypto;
 
   return Features;
 }