[Bug middle-end/18908] New: Missed folding opportunities with bools

[falk at debian dot org]

GNU C version 4.0.0 20041209 (experimental)

_Bool f1(const _Bool *p) { return *p & 1; }
_Bool f2(const _Bool *p) { return *p + 0; }
_Bool f3(_Bool *p) { *p ^= 1; }
_Bool f4(_Bool *p) { *p = ~*p; }

yields

f1:	ldbu    v0,0(a0)
	and     v0,0x1,v0
	ret

f2:	ldbu    v0,0(a0)
	cmpult  zero,v0,v0
	ret

f3:	ldbu    t0,0(a0)
	cmpeq   t0,0x1,t0
	cmpeq   t0,0,t0
	stb     t0,0(a0)
	ret

f4:	ldbu    t0,0(a0)
	not     t0,t0
	sextl   t0,t0
	cmpult  zero,t0,t0
	stb     t0,0(a0)
	ret

all of which contain at least one superfluous instruction.

-- 
           Summary: Missed folding opportunities with bools
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P2
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: falk at debian dot org
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: alphaev68-unknown-linux-gnu
  GCC host triplet: alphaev68-unknown-linux-gnu
GCC target triplet: alphaev68-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18908