Properly implement the CPU feature disabling in qsimd.cpp.

Don't use ^=, since that might enable a feature that wasn't detected.

The new use is:
    export QT_NO_CPU_FEATURE="<feature1> [<feature2>]"

Reviewed-by: Benjamin Poulain

1 files changed, 60 insertions, 97 deletions

diff --git a/src/corelib/tools/qsimd.cpp b/src/corelib/tools/qsimd.cpp
index 2472449..c34644c 100644
--- a/src/corelib/tools/qsimd.cpp
+++ b/src/corelib/tools/qsimd.cpp
@@ -112,11 +112,6 @@ static inline uint detectProcessorFeatures()
                 }
         }
 
-        if (qgetenv("QT_NO_IWMMXT").toInt())
-            features ^= IWMMXT;
-        if (qgetenv("QT_NO_NEON").toInt())
-            features ^= NEON;
-
         ::qt_safe_close(auxv);
         return features;
     }
@@ -125,11 +120,9 @@ static inline uint detectProcessorFeatures()
 
 #if defined(QT_HAVE_IWMMXT)
     // runtime detection only available when running as a previlegied process
-    static const bool doIWMMXT = !qgetenv("QT_NO_IWMMXT").toInt();
-    features = doIWMMXT ? IWMMXT : 0;
+    features = IWMMXT;
 #elif defined(QT_HAVE_NEON)
-    static const bool doNEON = !qgetenv("QT_NO_NEON").toInt();
-    features = doNEON ? NEON : 0;
+    features = NEON;
 #endif
 
     return features;
@@ -284,29 +277,6 @@ static inline uint detectProcessorFeatures()
     if (feature_result & (1u << 28))
         features |= AVX;
 
-#if defined(QT_HAVE_MMX)
-    if (qgetenv("QT_NO_MMX").toInt())
-        features ^= MMX;
-#endif
-    if (qgetenv("QT_NO_MMXEXT").toInt())
-        features ^= MMXEXT;
-
-#if defined(QT_HAVE_3DNOW)
-    if (qgetenv("QT_NO_3DNOW").toInt())
-        features ^= MMX3DNOW;
-#endif
-    if (qgetenv("QT_NO_3DNOWEXT").toInt())
-        features ^= MMX3DNOWEXT;
-
-#if defined(QT_HAVE_SSE)
-    if (qgetenv("QT_NO_SSE").toInt())
-        features ^= SSE;
-#endif
-#if defined(QT_HAVE_SSE2)
-    if (qgetenv("QT_NO_SSE2").toInt())
-        features ^= SSE2;
-#endif
-
     return features;
 }
 
@@ -358,28 +328,7 @@ static inline uint detectProcessorFeatures()
     if (feature_result & (1u << 28))
         features |= AVX;
 
-#if defined(QT_HAVE_MMX)
-    if (qgetenv("QT_NO_MMX").toInt())
-        features ^= MMX;
-#endif
-    if (qgetenv("QT_NO_MMXEXT").toInt())
-        features ^= MMXEXT;
-
-#if defined(QT_HAVE_3DNOW)
-    if (qgetenv("QT_NO_3DNOW").toInt())
-        features ^= MMX3DNOW;
-#endif
-    if (qgetenv("QT_NO_3DNOWEXT").toInt())
-        features ^= MMX3DNOWEXT;
-
-#if defined(QT_HAVE_SSE)
-    if (qgetenv("QT_NO_SSE").toInt())
-        features ^= SSE;
-#endif
-#if defined(QT_HAVE_SSE2)
-    if (qgetenv("QT_NO_SSE2").toInt())
-        features ^= SSE2;
-#endif
+    return features;
 }
 
 #elif defined(__ia64__)
@@ -395,64 +344,78 @@ static inline uint detectProcessorFeatures()
 }
 #endif
 
+/*
+ * Use kdesdk/scripts/generate_string_table.pl to update the table below.
+ * Here's the data (don't forget the ONE leading space):
+ mmx
+ mmxext
+ mmx3dnow
+ mmx3dnowext
+ sse
+ sse2
+ cmov
+ iwmmxt
+ neon
+ sse3
+ ssse3
+ sse4.1
+ sse4.2
+ avx
+  */
+
+// begin generated
+static const char features_string[] =
+    " mmx\0"
+    " mmxext\0"
+    " mmx3dnow\0"
+    " mmx3dnowext\0"
+    " sse\0"
+    " sse2\0"
+    " cmov\0"
+    " iwmmxt\0"
+    " neon\0"
+    " sse3\0"
+    " ssse3\0"
+    " sse4.1\0"
+    " sse4.2\0"
+    " avx\0"
+    "\0";
+
+static const int features_indices[] = {
+       0,    5,   13,   23,   36,   41,   47,   53,
+      61,   67,   73,   80,   88,   96,   -1
+};
+// end generated
+
+const int features_count = (sizeof features_indices - 1) / (sizeof features_indices[0]);
+
 uint qDetectCPUFeatures()
 {
     static QBasicAtomicInt features = Q_BASIC_ATOMIC_INITIALIZER(-1);
     if (features != -1)
         return features;
 
-    features = detectProcessorFeatures();
+    uint f = detectProcessorFeatures();
+    QByteArray disable = qgetenv("QT_NO_CPU_FEATURE");
+    if (!disable.isEmpty()) {
+        disable.prepend(' ');
+        for (int i = 0; i < features_count; ++i) {
+            if (disable.contains(features_string + features_indices[i]))
+                f &= ~(1 << i);
+        }
+    }
+
+    features = f;
     return features;
 }
 
 void qDumpCPUFeatures()
 {
-    /*
-     * Use kdesdk/scripts/generate_string_table.pl to update the table below.
-     * Here's the data:
-mmx
-mmxext
-mmx3dnow
-mmx3dnowext
-sse
-sse2
-cmov
-iwmmxt
-neon
-sse3
-ssse3
-sse4.1
-sse4.2
-avx
-      */
-    static const char features_string[] =
-        "mmx\0"
-        "mmxext\0"
-        "mmx3dnow\0"
-        "mmx3dnowext\0"
-        "sse\0"
-        "sse2\0"
-        "cmov\0"
-        "iwmmxt\0"
-        "neon\0"
-        "sse3\0"
-        "ssse3\0"
-        "sse4.1\0"
-        "sse4.2\0"
-        "avx\0"
-        "\0";
-
-    static const int features_indices[] = {
-           0,    4,   11,   20,   32,   36,   41,   46,
-          53,   58,   63,   69,   76,   83,   -1
-    };
-    const int features_count = (sizeof features_indices - 1) / (sizeof features_indices[0]);
-
     uint features = qDetectCPUFeatures();
     printf("Processor features: ");
     for (int i = 0; i < features_count; ++i) {
         if (features & (1 << i))
-            printf(" %s", features_string + features_indices[i]);
+            printf("%s", features_string + features_indices[i]);
     }
     puts("");
 }