> -----Original Message----- > From: Richard Guenther [mailto:richard.guent...@gmail.com] > Sent: Friday, September 02, 2011 5:07 PM > To: Jiangning Liu > Cc: gcc@gcc.gnu.org > Subject: Re: Is VRP is too conservative to identify boolean value 0 and > 1? > > On Fri, Sep 2, 2011 at 7:58 AM, Jiangning Liu <jiangning....@arm.com> > wrote: > > Hi, > > > > For the following small case, > > > > int f(int i, int j) > > { > > if (i==1 && j==2) > > return i; > > else > > return j; > > } > > > > with -O2 option, GCC has vrp2 dump like below, > > > > ====================== > > > > Value ranges after VRP: > > > > i_1: VARYING > > i_2(D): VARYING > > D.1249_3: [0, +INF] > > j_4(D): VARYING > > D.1250_5: [0, +INF] > > D.1251_6: [0, +INF] > > j_10: [2, 2] EQUIVALENCES: { j_4(D) } (1 elements) > > > > > > Removing basic block 3 > > f (int i, int j) > > { > > _Bool D.1251; > > _Bool D.1250; > > _Bool D.1249; > > > > <bb 2>: > > D.1249_3 = i_2(D) == 1; > > D.1250_5 = j_4(D) == 2; > > D.1251_6 = D.1250_5 & D.1249_3; > > if (D.1251_6 != 0) > > goto <bb 3>; > > else > > goto <bb 4>; > > > > <bb 3>: > > > > <bb 4>: > > # i_1 = PHI <1(3), j_4(D)(2)> > > return i_1; > > > > } > > > > ======================== > > > > Variable D.1249_3, D.1250_5 and D.1251_6 should be boolean values, so > the > > their value ranges should be > > > > D.1249_3: [0, 1] > > D.1250_5: [0, 1] > > D.1251_6: [0, 1] > > > > So why current VRP can't find out this value range? > > It does - it just prints it as [0, +INF], they are bools with > TYPE_MAX_VALUE > == 1 after all.
Richard, May I use REG_EXPR(rtx of D.1249_3) in xxx.md file to detect whether D.1249_3 is a bool or not? Some comments in GCC says REG_EXPR may be lost in back-end. True? If we do have REG_EXPR info for some cases in back-end, is it guaranteed to be correct? May I implementing back-end peephole optimization depending on REG_EXPR? Thanks, -Jiangning > > Richard. > > > > > I'm asking this question because the optimizations in back-end need > this > > info to do advanced optimization. > > > > Thanks, > > -Jiangning > > > > > >
