Fix initialisation order for ID register fields.

Making the constructor `constexpr` gives these "constant" rather than
"dynamic" initialisation, which guarantees that they'll be initialised
before any other dynamically-initialised static variables.

This makes it safe to make static variable initialisers dependent on the
result of `CPUFeatures::InferFromOS()` and similar functions.

Change-Id: Ib65e92273c7ac03d07e17cbe844b598ef3bc60ac

1 files changed, 5 insertions, 1 deletions

diff --git a/src/aarch64/cpu-aarch64.h b/src/aarch64/cpu-aarch64.h
index 74b23934..2bf1e60f 100644
--- a/src/aarch64/cpu-aarch64.h
+++ b/src/aarch64/cpu-aarch64.h
@@ -56,7 +56,11 @@ class IDRegister {
    public:
     enum Type { kUnsigned, kSigned };
 
-    explicit Field(int lsb, Type type = kUnsigned) : lsb_(lsb), type_(type) {}
+    // This needs to be constexpr so that fields have "constant initialisation".
+    // This avoids initialisation order problems when these values are used to
+    // (dynamically) initialise static variables, etc.
+    explicit constexpr Field(int lsb, Type type = kUnsigned)
+        : lsb_(lsb), type_(type) {}
 
     static const int kMaxWidthInBits = 4;