X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Fcmm%2FCmmOpt.hs;h=df0555fe58f027e963e283196e31c64d5830ddf6;hb=c9629e9f5e4957c8665fc2497b5e769b769cb7d3;hp=53281b031266c6df33604a71b6fefd455ff5ee1a;hpb=889c084e943779e76d19f2ef5e970ff655f511eb;p=ghc-hetmet.git

diff --git a/compiler/cmm/CmmOpt.hs b/compiler/cmm/CmmOpt.hs
index 53281b0..df0555f 100644
--- a/compiler/cmm/CmmOpt.hs
+++ b/compiler/cmm/CmmOpt.hs
@@ -306,9 +306,18 @@ cmmMachOpFold op [x@(CmmLit _), y]
 -- PicBaseReg from the corresponding label (or label difference).
 --
 cmmMachOpFold mop1 [CmmMachOp mop2 [arg1,arg2], arg3]
-   | mop1 == mop2 && isAssociativeMachOp mop1
+   | mop2 `associates_with` mop1
      && not (isLit arg1) && not (isPicReg arg1)
-   = cmmMachOpFold mop1 [arg1, cmmMachOpFold mop2 [arg2,arg3]]
+   = cmmMachOpFold mop2 [arg1, cmmMachOpFold mop1 [arg2,arg3]]
+   where
+     MO_Add{} `associates_with` MO_Sub{} = True
+     mop1 `associates_with` mop2 =
+        mop1 == mop2 && isAssociativeMachOp mop1
+
+-- special case: (a - b) + c  ==>  a + (c - b)
+cmmMachOpFold mop1@(MO_Add{}) [CmmMachOp mop2@(MO_Sub{}) [arg1,arg2], arg3]
+   | not (isLit arg1) && not (isPicReg arg1)
+   = cmmMachOpFold mop1 [arg1, cmmMachOpFold mop2 [arg3,arg2]]
 
 -- Make a RegOff if we can
 cmmMachOpFold (MO_Add _) [CmmReg reg, CmmLit (CmmInt n rep)]
@@ -431,10 +440,10 @@ cmmMachOpFold mop args@[x, y@(CmmLit (CmmInt n _))]
   = case mop of
     	MO_Mul rep
 	   | Just p <- exactLog2 n ->
-                 CmmMachOp (MO_Shl rep) [x, CmmLit (CmmInt p rep)]
+                 cmmMachOpFold (MO_Shl rep) [x, CmmLit (CmmInt p rep)]
     	MO_U_Quot rep
 	   | Just p <- exactLog2 n ->
-                 CmmMachOp (MO_U_Shr rep) [x, CmmLit (CmmInt p rep)]
+                 cmmMachOpFold (MO_U_Shr rep) [x, CmmLit (CmmInt p rep)]
     	MO_S_Quot rep
 	   | Just p <- exactLog2 n, 
 	     CmmReg _ <- x ->	-- We duplicate x below, hence require
@@ -462,7 +471,7 @@ cmmMachOpFold mop args@[x, y@(CmmLit (CmmInt n _))]
 			 CmmMachOp (MO_And rep) [x1, CmmLit (CmmInt (n-1) rep)]
 		    x3 = CmmMachOp (MO_Add rep) [x, x2]
 		in
-                CmmMachOp (MO_S_Shr rep) [x3, CmmLit (CmmInt p rep)]
+                cmmMachOpFold (MO_S_Shr rep) [x3, CmmLit (CmmInt p rep)]
     	other
            -> unchanged
     where