feat: add NCNN_ISA environment variable cache for ARM ISA feature checks

This commit adds a cache mechanism for various ARM ISA feature checks using NCNN_ISA environment variables.
The `get_isa_env` results are now cached in static variables at the file level.

Signed-off-by: Kaiyao Duan <[email protected]>

src/cpu.cpp

@@ -1893,6 +1893,22 @@ static int get_isa_env(const char* isa_flags)
     return false;
 }
 
+#if (__aarch64__ || __arm__)
+    static int is_cpu_arm_cpuid_disabled = get_isa_env("-cpuid");
+    static int is_cpu_arm_asimdhp_disabled = get_isa_env("-asimdhp");
+    static int is_cpu_arm_asimddp_disabled = get_isa_env("-asimddp");
+    static int is_cpu_arm_asimdfhm_disabled = get_isa_env("-asimdfhm");
+    static int is_cpu_arm_bf16_disabled = get_isa_env("-bf16");
+    static int is_cpu_arm_i8mm_disabled = get_isa_env("-i8mm");
+    static int is_cpu_arm_sve_disabled = get_isa_env("-sve");
+    static int is_cpu_arm_sve2_disabled = get_isa_env("-sve2");
+    static int is_cpu_arm_svebf16_disabled = get_isa_env("-svebf16");
+    static int is_cpu_arm_svei8mm_disabled = get_isa_env("-svei8mm");
+    static int is_cpu_arm_svef32mm_disabled = get_isa_env("-svef32mm");
+    static int is_cpu_arm_edsp_disabled = get_isa_env("-edsp");
+    static int is_cpu_arm_vfpv4_disabled = get_isa_env("-vfpv4");
+#endif
+
 // the initialization
 static void initialize_global_cpu_info()
 {
@@ -2121,7 +2137,7 @@ int cpu_support_arm_edsp()
 {
     try_initialize_global_cpu_info();
 #if __arm__ && !__aarch64__
-    if (get_isa_env("-edsp"))
+    if (is_cpu_arm_edsp_disabled)
         return 0;
 #if defined _WIN32
     return g_cpu_support_arm_edsp;
@@ -2143,7 +2159,7 @@ int cpu_support_arm_neon()
 #if __aarch64__
     return 1;
 #elif __arm__
-    if (get_isa_env("-neon"))
+    if (is_cpu_arm_neon_disabled)
         return 0;
 #if defined _WIN32
     return g_cpu_support_arm_neon;
@@ -2165,7 +2181,7 @@ int cpu_support_arm_vfpv4()
 #if __aarch64__
     return 1;
 #elif __arm__
-    if (get_isa_env("-vfpv4"))
+    if (is_cpu_arm_vfpv4_disabled)
         return 0;
 #if defined _WIN32
     return g_cpu_support_arm_vfpv4;
@@ -2185,7 +2201,7 @@ int cpu_support_arm_asimdhp()
 {
     try_initialize_global_cpu_info();
 #if __aarch64__
-    if (get_isa_env("-asimdhp"))
+    if (is_cpu_arm_asimdhp_disabled)
         return 0;
 #if defined _WIN32
     return g_cpu_support_arm_asimdhp;
@@ -2215,7 +2231,7 @@ int cpu_support_arm_cpuid()
 {
     try_initialize_global_cpu_info();
 #if __aarch64__
-    if (get_isa_env("-cpuid"))
+    if (is_cpu_arm_cpuid_disabled)
         return 0;
 #if defined _WIN32
     return g_cpu_support_arm_cpuid;
@@ -2235,7 +2251,7 @@ int cpu_support_arm_asimddp()
 {
     try_initialize_global_cpu_info();
 #if __aarch64__
-    if (get_isa_env("-asimddp"))
+    if (is_cpu_arm_asimddp_disabled)
         return 0;
 #if defined _WIN32
     return g_cpu_support_arm_asimddp;
@@ -2263,7 +2279,7 @@ int cpu_support_arm_asimdfhm()
 {
     try_initialize_global_cpu_info();
 #if __aarch64__
-    if (get_isa_env("-asimdfhm"))
+    if (is_cpu_arm_asimdfhm_disabled)
         return 0;
 #if defined _WIN32
     return g_cpu_support_arm_asimdfhm;
@@ -2291,7 +2307,7 @@ int cpu_support_arm_bf16()
 {
     try_initialize_global_cpu_info();
 #if __aarch64__
-    if (get_isa_env("-bf16"))
+    if (is_cpu_arm_bf16_disabled)
         return 0;
 #if defined _WIN32
     return g_cpu_support_arm_bf16;
@@ -2317,7 +2333,7 @@ int cpu_support_arm_i8mm()
 {
     try_initialize_global_cpu_info();
 #if __aarch64__
-    if (get_isa_env("-i8mm"))
+    if (is_cpu_arm_i8mm_disabled)
         return 0;
 #if defined _WIN32
     return g_cpu_support_arm_i8mm;
@@ -2343,7 +2359,7 @@ int cpu_support_arm_sve()
 {
     try_initialize_global_cpu_info();
 #if __aarch64__
-    if (get_isa_env("-sve"))
+    if (is_cpu_arm_sve_disabled)
         return 0;
 #if defined _WIN32
     return g_cpu_support_arm_sve;
@@ -2363,7 +2379,7 @@ int cpu_support_arm_sve2()
 {
     try_initialize_global_cpu_info();
 #if __aarch64__
-    if (get_isa_env("-sve2"))
+    if (is_cpu_arm_sve2_disabled)
         return 0;
 #if defined _WIN32
     return g_cpu_support_arm_sve2;
@@ -2383,7 +2399,7 @@ int cpu_support_arm_svebf16()
 {
     try_initialize_global_cpu_info();
 #if __aarch64__
-    if (get_isa_env("-svebf16"))
+    if (is_cpu_arm_svebf16_disabled)
         return 0;
 #if defined _WIN32
     return g_cpu_support_arm_svebf16;
@@ -2403,7 +2419,7 @@ int cpu_support_arm_svei8mm()
 {
     try_initialize_global_cpu_info();
 #if __aarch64__
-    if (get_isa_env("-svei8mm"))
+    if (is_cpu_arm_svei8mm_disabled)
         return 0;
 #if defined _WIN32
     return g_cpu_support_arm_svei8mm;
@@ -2423,7 +2439,7 @@ int cpu_support_arm_svef32mm()
 {
     try_initialize_global_cpu_info();
 #if __aarch64__
-    if (get_isa_env("-svef32mm"))
+    if (is_cpu_arm_svef32mm_disabled)
         return 0;
 #if defined _WIN32
     return g_cpu_support_arm_svef32mm;