JIT: Use rsb and shift in easy multiply.

For easy multiplication using reverse subtract (when
lit is 2^n-1) use the barrel shifter for rsb.

This improves arithmetic performance for code executing
in Dalvik. E.g String.hashCode.

Change-Id: Ifb086dcec344b30fd3e392ac21d508b43e820cdc
Signed-off-by: Patrik Ryd <patrik.ryd@stericsson.com>

1 files changed, 1 insertions, 4 deletions

diff --git a/vm/compiler/codegen/arm/CodegenDriver.cpp b/vm/compiler/codegen/arm/CodegenDriver.cpp
index f8570c435..44a48f7d0 100644
--- a/vm/compiler/codegen/arm/CodegenDriver.cpp
+++ b/vm/compiler/codegen/arm/CodegenDriver.cpp
@@ -2257,10 +2257,7 @@ static bool handleEasyMultiply(CompilationUnit *cUnit,
     } else {
         // Reverse subtract: (src << (shift + 1)) - src.
         assert(powerOfTwoMinusOne);
-        // TODO: rsb dst, src, src lsl#lowestSetBit(lit + 1)
-        int tReg = dvmCompilerAllocTemp(cUnit);
-        opRegRegImm(cUnit, kOpLsl, tReg, rlSrc.lowReg, lowestSetBit(lit + 1));
-        opRegRegReg(cUnit, kOpSub, rlResult.lowReg, tReg, rlSrc.lowReg);
+        genMultiplyByShiftAndReverseSubtract(cUnit, rlSrc, rlResult, lowestSetBit(lit + 1));
     }
     storeValue(cUnit, rlDest, rlResult);
     return true;