Richard Biener <richard.guent...@gmail.com> writes: > Nick Clifton <ni...@redhat.com> wrote: >>Hi Guys, >> >> I have tracked down a bug reported against the MSP430 (PR >> target/59613) which turns out to be a generic problem. The function >> get_mode_bounds() in stor-layout.c computes the minimum and maximum >> values for a given mode, but it uses the bitsize of the mode not the >> precision. This is incorrect if the two values are different, (which >> can happen when the target is using partial integer modes), since >> values outside of the precision cannot be stored in the mode, no >> matter how many bits the mode uses. >> >> The result, for the MSP430 in LARGE mode, is that calling >> get_mode_bounds() on PSImode returns a maximum value of -1 instead of >> 1^20. Note - what happens is that get_mode_bounds computes the >> maximum as (1 << 31) - 1 and then calls gen_int_mode to create an RTX >> for this value. But gen_int_mode calls trunc_int_for_mode which uses >> GET_MODE_PRECISION to determine the sign bits and these bits overwrite >> some of the zero bits in (1 << 31) - 1 changing it into -1. >> >> The result of this behaviour is the bug that I was tracking down. >> simplify_const_relational_operation() was erroneously discarding a >> comparison of a pointer against zero, because get_mode_bounds told it >> that the pointer could only have values between 0 and -1... >> >> The proposed patch is simple - use the mode's precision and not its >> bitsize to compute the bounds. This seems like an obvious fix, but >> I am not familiar with all of the uses of get_mode_bounds() so maybe >> there is a situation where using the bitsize is correct. >> >> There were no regressions and several fixed test cases with the >> msp430-elf toolchain that I was using, and no regressions with an >> i686-pc-linux-gnu toolchain. >> >> OK to apply ? > > Ok without the comment (this is obvious)
This completely breaks ia64, see PR59649. Andreas. -- Andreas Schwab, sch...@linux-m68k.org GPG Key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5 "And now for something completely different."
