http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57439
--- Comment #13 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
(In reply to Jorn Wolfgang Rennecke from comment #10)
> Created attachment 30212 [details]
> experimental patch for execute/pr42721.c failure
The patch is OK but let's beef up the comment a little bit:
+ if (mode != reg_mode[regno])
+ {
+ if (!MODES_OK_FOR_MOVE2ADD (mode, reg_mode[regno]))
+ return false;
+ /* For big endian, the starting regno for the subreg might be
+ different. */
/* The value loaded into regno in reg_mode[regno] is also valid in
mode after truncation only if (REG:mode regno) is the lowpart of
(REG:reg_mode[regno] regno). Now, for big endian, the starting
regno of the lowpart might be different. */
+ int s_off = subreg_lowpart_offset (mode, reg_mode[regno]);
+ s_off = subreg_regno_offset (regno, reg_mode[regno], s_off, mode);
+ if (s_off != 0)
+ /* We could in principle adjust regno, check reg_mode[regno] to be
+ BLKmode, and return s_off to the caller (vs. -1 for failure),
+ but we currently have no callers that could make use of this
+ information. */
+ return false;
+ }
