* Big speedup (factor > 2.5) in all nix-env operations that do actual

  instantiation, e.g. "nix-env -i" and "nix-env -qas" (but not
  "nix-env -qa").  It turns out that many redundant calls to
  addToStore(path) were made, which reads and hashes the entire path.
  For instance, the bash bootstrap binary in Nixpkgs would be read and
  hashed many times.  As a result nix-env would spend around 92% of
  its time in the function sha256_block (according to callgrind).
  Some simple memoization fixes this.

2 files changed, 14 insertions, 3 deletions

diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 11185159c123..602f63fdedaf 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -11,6 +11,10 @@
 typedef map<Path, PathSet> DrvRoots;
 typedef map<Path, Hash> DrvHashes;
 
+/* Cache for calls to addToStore(); maps source paths to the store
+   paths. */
+typedef map<Path, Path> SrcToStore;
+
 struct EvalState;
 
 /* Note: using a ATermVector is safe here, since when we call a primop
@@ -24,6 +28,7 @@ struct EvalState
     ATermMap primOps;
     DrvRoots drvRoots;
     DrvHashes drvHashes; /* normalised derivation hashes */
+    SrcToStore srcToStore; 
     Expr blackHole;
 
     unsigned int nrEvaluated;
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 31fff0b493e8..77721a5a8d87 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -165,9 +165,15 @@ static void processBinding(EvalState & state, Expr e, Derivation & drv,
             if (isDerivation(srcPath))
                 throw Error(format("file names are not allowed to end in `%1%'")
                     % drvExtension);
-            Path dstPath(addToStore(srcPath));
-            printMsg(lvlChatty, format("copied source `%1%' -> `%2%'")
-                % srcPath % dstPath);
+            Path dstPath;
+            if (state.srcToStore[srcPath] != "")
+                dstPath = state.srcToStore[srcPath];
+            else {
+                dstPath = addToStore(srcPath);
+                state.srcToStore[srcPath] = dstPath;
+                printMsg(lvlChatty, format("copied source `%1%' -> `%2%'")
+                    % srcPath % dstPath);
+            }
             drv.inputSrcs.insert(dstPath);
             ss.push_back(dstPath);
         }