Avoid needlessly splitting a UniqSupply when extracting a Unique (#8041)

In many places, 'splitUniqSupply' + 'uniqFromSupply' is used to split a
UniqSupply into a Unique and a new UniqSupply. In such places we should
instead use the more efficient and more appropriate
'takeUniqFromSupply' (or equivalent).

Not only is the former method slower, it also generates and throws away
an extra Unique.

Signed-off-by: Austin Seipp <aseipp@pobox.com>

2 files changed, 6 insertions, 5 deletions

diff --git a/compiler/codeGen/StgCmmExpr.hs b/compiler/codeGen/StgCmmExpr.hs
index d7edf8e193..3d60def450 100644
--- a/compiler/codeGen/StgCmmExpr.hs
+++ b/compiler/codeGen/StgCmmExpr.hs
@@ -43,7 +43,6 @@ import Maybes
 import Util
 import FastString
 import Outputable
-import UniqSupply
 
 import Control.Monad (when,void)
 
@@ -70,8 +69,8 @@ cgExpr (StgLit lit)       = do cmm_lit <- cgLit lit
 
 cgExpr (StgLet binds expr)             = do { cgBind binds;     cgExpr expr }
 cgExpr (StgLetNoEscape _ _ binds expr) =
-  do { us <- newUniqSupply
-     ; let join_id = mkBlockId (uniqFromSupply us)
+  do { u <- newUnique
+     ; let join_id = mkBlockId u
      ; cgLneBinds join_id binds
      ; r <- cgExpr expr
      ; emitLabel join_id
diff --git a/compiler/codeGen/StgCmmMonad.hs b/compiler/codeGen/StgCmmMonad.hs
index 3f361e3f51..251b679078 100644
--- a/compiler/codeGen/StgCmmMonad.hs
+++ b/compiler/codeGen/StgCmmMonad.hs
@@ -446,8 +446,10 @@ newUniqSupply = do
 
 newUnique :: FCode Unique
 newUnique = do
-        us <- newUniqSupply
-        return (uniqFromSupply us)
+        state <- getState
+        let (u,us') = takeUniqFromSupply (cgs_uniqs state)
+        setState $ state { cgs_uniqs = us' }
+        return u
 
 ------------------
 getInfoDown :: FCode CgInfoDownwards