debListParser: Cache `essential` and `myArch` more

Lookup these variables in the constructor once, rather than
once per package.

This requires a bit of care as debListParser::UsePackage()
defaults to "all" for essential when unset, hence we simply
change its == "all" comparisons to == "all" || .empty().#

This removes any per-paragraph configuration lookups
from the file parser.

Also parse myArch from ParseProvides down to ParseDepends()
as that call ended up causing it to query APT::Architecture
*again* since the function we call is static.

Together, the removed config lookups safe about 2.3% of
cache generation runtime.

1 files changed, 2 insertions, 2 deletions

diff --git a/apt-pkg/deb/deblistparser.h b/apt-pkg/deb/deblistparser.h
index ff1bfa06c..2a9108775 100644
--- a/apt-pkg/deb/deblistparser.h
+++ b/apt-pkg/deb/deblistparser.h
@@ -36,13 +36,13 @@ class APT_HIDDEN debListParser : public pkgCacheListParser
       unsigned char Val;
    };
 
-   private:
+   protected:
    std::vector<std::string> forceEssential;
    std::vector<std::string> forceImportant;
    std::string MD5Buffer;
    std::string myArch;
+   std::string essential;
 
-   protected:
    pkgTagFile Tags;
    pkgTagSection Section;
    map_filesize_t iOffset;