Fold Add8(t,t) ==> t << 1. Fixes #143817 (Unused bitfield pad bits

confuse memcheck)

git-svn-id: svn://svn.valgrind.org/vex/trunk@1747

diff --git a/VEX/priv/ir/iropt.c b/VEX/priv/ir/iropt.c
index 40c7888163c089f74f62a632f25de0dab68875ab..db7aa6b0bcab7e359cfc79794ccee486874fde0c 100644 (file)
--- a/VEX/priv/ir/iropt.c
+++ b/VEX/priv/ir/iropt.c
@@ -1432,6 +1432,18 @@ static IRExpr* fold_Expr ( IRExpr* e )
                               IRExpr_Const(IRConst_U8(1)));
          } else
 
+         /* Add8(t,t) ==> t << 1;  rationale as for Add32(t,t) above. */
+         if (e->Iex.Binop.op == Iop_Add8
+             && e->Iex.Binop.arg1->tag == Iex_RdTmp
+             && e->Iex.Binop.arg2->tag == Iex_RdTmp
+             && e->Iex.Binop.arg1->Iex.RdTmp.tmp 
+                == e->Iex.Binop.arg2->Iex.RdTmp.tmp) {
+            e2 = IRExpr_Binop(Iop_Shl8,
+                              e->Iex.Binop.arg1,
+                              IRExpr_Const(IRConst_U8(1)));
+         } else
+         /* NB no Add16(t,t) case yet as no known test case exists */
+
          /* Or64/Add64(x,0) ==> x */
          if ((e->Iex.Binop.op == Iop_Add64 || e->Iex.Binop.op == Iop_Or64)
              && e->Iex.Binop.arg2->tag == Iex_Const