On Thu, Aug 7, 2014 at 7:24 AM, Kugan <kugan.vivekanandara...@linaro.org> wrote: > On 06/08/14 23:29, Richard Biener wrote: >> On Wed, Aug 6, 2014 at 3:21 PM, Kugan <kugan.vivekanandara...@linaro.org> >> wrote: >>> On 06/08/14 22:09, Richard Biener wrote: >>>> On Tue, Aug 5, 2014 at 4:21 PM, Jakub Jelinek <ja...@redhat.com> wrote: >>>>> On Tue, Aug 05, 2014 at 04:17:41PM +0200, Richard Biener wrote: >>>>>> what's the semantic of setting SRP_SIGNED_AND_UNSIGNED >>>>>> on the subreg? That is, for the created (subreg:lhs_mode >>>>>> (reg:<PROMOTE_MODE of ssa> N))? >>>>> >>>>> SRP_SIGNED_AND_UNSIGNED on a subreg should mean that >>>>> the subreg is both zero and sign extended, which means >>>>> that the topmost bit of the narrower mode is known to be zero, >>>>> and all bits above it in the wider mode are known to be zero too. >>>>> SRP_SIGNED means that the topmost bit of the narrower mode is >>>>> either 0 or 1 and depending on that the above wider mode bits >>>>> are either all 0 or all 1. >>>>> SRP_UNSIGNED means that regardless of the topmost bit value, >>>>> all above wider mode bits are 0. >>>> >>>> Ok, then from the context of the patch we already know that >>>> either SRP_UNSIGNED or SRP_SIGNED is true which means >>>> that the value is sign- or zero-extended. >>>> >>>> I suppose inside promoted_for_type_p >>>> TYPE_MODE (TREE_TYPE (ssa)) == lhs_mode, I'm not sure >>>> why you pass !unsignedp as lhs_uns. >>> >>> In expand_expr_real_1, it is already known that it is promoted for >>> unsigned_p and we are setting SUBREG_PROMOTED_SET (temp, unsignedp). >>> >>> If we can prove that it is also promoted for !unsignedp, we can set >>> SUBREG_PROMOTED_SET (temp, SRP_SIGNED_AND_UNSIGNED). >>> >>> promoted_for_type_p should prove this based on the value range info. >>> >>>> >>>> Now, from 'ssa' alone we can't tell anything about a larger mode >>>> registers value if that is either zero- or sign-extended. But we >>>> know that those bits are properly zero-extended if unsignedp >>>> and properly sign-extended if !unsignedp? >>>> >>>> So what the predicate tries to prove is that sign- and zero-extending >>>> results in the same larger-mode value. This is true if the >>>> MSB of the smaller mode is not set. >>>> >>>> Let's assume that smaller mode is that of 'ssa' then the test >>>> is just >>>> >>>> return (!tree_int_cst_sign_bit (min) && !tree_int_cst_sign_bit (max)); >>>> >>>> no? >>> >>> hmm, is this because we will never have a call to promoted_for_type_p >>> with same sign (ignoring PROMOTE_MODE) for 'ssa' and the larger mode. >>> The case with larger mode signed and 'ssa' unsigned will not work. >>> Therefore larger mode unsigned and 'ssa' signed will be the only case >>> that we should consider. >>> >>> However, with PROMOTE_MODE, isnt that we will miss some cases with this. >> >> No, PROMOTE_MODE will still either sign- or zero-extend. If either >> results in zeros in the upper bits then PROMOTE_MODE doesn't matter. >> > > Thanks for the explanation. Please find the attached patch that > implements this. I have updated the comments and predicate to match this. > > Bootstrap tested on x86_64-unknown-linux-gnu and regression tested on > x86_64-unknown-linux-gnu and arm-none-linux-gnueabi with no new > regressions. Is this OK?
Ok with changing + || (TYPE_PRECISION (TREE_TYPE (ssa)) > GET_MODE_PRECISION (mode))) + return false; to check with != (does that even happen?) Thanks, Richard. > Thanks, > Kugan > > gcc/ > 2014-08-07 Kugan Vivekanandarajah <kug...@linaro.org> > > * calls.c (precompute_arguments): Check > promoted_for_signed_and_unsigned_p and set the promoted mode. > (promoted_for_signed_and_unsigned_p): New function. > (expand_expr_real_1): Check promoted_for_signed_and_unsigned_p > and set the promoted mode. > * expr.h (promoted_for_signed_and_unsigned_p): New function > definition. > * cfgexpand.c (expand_gimple_stmt_1): Call emit_move_insn if > SUBREG is promoted with SRP_SIGNED_AND_UNSIGNED. > > > gcc/testsuite > 2014-08-07 Kugan Vivekanandarajah <kug...@linaro.org> > > * gcc.dg/zero_sign_ext_test.c: New test. > >
