Fix performance degradation introduced by the second expansion feature.

I did this by adding intelligence into the algorithm such that the
second expansion was only actually performed when the prerequisite list
contained at least one "$", so we knew it is actually needed.

Without this we were using up a LOT more memory, since every single
target (even ones never used by make) had their file variables
initialized.  This also used a lot more CPU, since we needed to create
and populate a new variable hash table for every target.

There is one issue remaining with this feature: it leaks memory.  In
pattern_search() we now initialize the file variables for every pattern
target, which allocates a hash table, etc.  However, sometimes we
recursively invoke pattern_search() (for intermediate files) with an
automatic variable (alloca() I believe) as the file.  When that function
returns, obviously, the file variable hash memory is lost.

1 files changed, 1 insertions, 0 deletions

diff --git a/dep.h b/dep.h
index 01c31a3..7e6a853 100644
--- a/dep.h
+++ b/dep.h
@@ -40,6 +40,7 @@ struct dep
     struct file *file;
     unsigned int changed : 8;
     unsigned int ignore_mtime : 1;
+    unsigned int need_2nd_expansion : 1;
   };