Ping again. On Fri, 2023-08-18 at 13:04 +0200, Stefan Schulze Frielinghaus via Gcc-patches wrote: > Ping. Since this fixes bootstrap problem PR110939 for Loongarch I'm > pingen this one earlier. > > On Thu, Aug 10, 2023 at 03:04:03PM +0200, Stefan Schulze Frielinghaus wrote: > > In the former fix in commit 41ef5a34161356817807be3a2e51fbdbe575ae85 I > > completely missed the fact that the normal form of a generated constant for > > a > > mode with fewer bits than in HOST_WIDE_INT is a sign extended version of the > > actual constant. This even holds true for unsigned constants. > > > > Fixed by masking out the upper bits for the incoming constant and sign > > extending the resulting unsigned constant. > > > > Bootstrapped and regtested on x64 and s390x. Ok for mainline? > > > > While reading existing optimizations in combine I stumbled across two > > optimizations where either my intuition about the representation of > > unsigned integers via a const_int rtx is wrong, which then in turn would > > probably also mean that this patch is wrong, or that the optimizations > > are missed sometimes. In other words in the following I would assume > > that the upper bits are masked out: > > > > diff --git a/gcc/combine.cc b/gcc/combine.cc > > index 468b7fde911..80c4ff0fbaf 100644 > > --- a/gcc/combine.cc > > +++ b/gcc/combine.cc > > @@ -11923,7 +11923,7 @@ simplify_compare_const (enum rtx_code code, > > machine_mode mode, > > /* (unsigned) < 0x80000000 is equivalent to >= 0. */ > > else if (is_a <scalar_int_mode> (mode, &int_mode) > > && GET_MODE_PRECISION (int_mode) - 1 < HOST_BITS_PER_WIDE_INT > > - && ((unsigned HOST_WIDE_INT) const_op > > + && (((unsigned HOST_WIDE_INT) const_op & GET_MODE_MASK > > (int_mode)) > > == HOST_WIDE_INT_1U << (GET_MODE_PRECISION (int_mode) - > > 1))) > > { > > const_op = 0; > > @@ -11962,7 +11962,7 @@ simplify_compare_const (enum rtx_code code, > > machine_mode mode, > > /* (unsigned) >= 0x80000000 is equivalent to < 0. */ > > else if (is_a <scalar_int_mode> (mode, &int_mode) > > && GET_MODE_PRECISION (int_mode) - 1 < HOST_BITS_PER_WIDE_INT > > - && ((unsigned HOST_WIDE_INT) const_op > > + && (((unsigned HOST_WIDE_INT) const_op & GET_MODE_MASK > > (int_mode)) > > == HOST_WIDE_INT_1U << (GET_MODE_PRECISION (int_mode) - > > 1))) > > { > > const_op = 0; > > > > For example, while bootstrapping on x64 the optimization is missed since > > a LTU comparison in QImode is done and the constant equals > > 0xffffffffffffff80. > > > > Sorry for inlining another patch, but I would really like to make sure > > that my understanding is correct, now, before I come up with another > > patch. Thus it would be great if someone could shed some light on this. > > > > gcc/ChangeLog: > > > > * combine.cc (simplify_compare_const): Properly handle unsigned > > constants while narrowing comparison of memory and constants. > > --- > > gcc/combine.cc | 19 ++++++++++--------- > > 1 file changed, 10 insertions(+), 9 deletions(-) > > > > diff --git a/gcc/combine.cc b/gcc/combine.cc > > index e46d202d0a7..468b7fde911 100644 > > --- a/gcc/combine.cc > > +++ b/gcc/combine.cc > > @@ -12003,14 +12003,15 @@ simplify_compare_const (enum rtx_code code, > > machine_mode mode, > > && !MEM_VOLATILE_P (op0) > > /* The optimization makes only sense for constants which are big > > enough > > so that we have a chance to chop off something at all. */ > > - && (unsigned HOST_WIDE_INT) const_op > 0xff > > - /* Bail out, if the constant does not fit into INT_MODE. */ > > - && (unsigned HOST_WIDE_INT) const_op > > - < ((HOST_WIDE_INT_1U << (GET_MODE_PRECISION (int_mode) - 1) << 1) > > - 1) > > + && ((unsigned HOST_WIDE_INT) const_op & GET_MODE_MASK (int_mode)) > > > 0xff > > /* Ensure that we do not overflow during normalization. */ > > - && (code != GTU || (unsigned HOST_WIDE_INT) const_op < > > HOST_WIDE_INT_M1U)) > > + && (code != GTU > > + || ((unsigned HOST_WIDE_INT) const_op & GET_MODE_MASK (int_mode)) > > + < HOST_WIDE_INT_M1U) > > + && trunc_int_for_mode (const_op, int_mode) == const_op) > > { > > - unsigned HOST_WIDE_INT n = (unsigned HOST_WIDE_INT) const_op; > > + unsigned HOST_WIDE_INT n > > + = (unsigned HOST_WIDE_INT) const_op & GET_MODE_MASK (int_mode); > > enum rtx_code adjusted_code; > > > > /* Normalize code to either LEU or GEU. */ > > @@ -12051,15 +12052,15 @@ simplify_compare_const (enum rtx_code code, > > machine_mode mode, > > HOST_WIDE_INT_PRINT_HEX ") to (MEM %s " > > HOST_WIDE_INT_PRINT_HEX ").\n", GET_MODE_NAME (int_mode), > > GET_MODE_NAME (narrow_mode_iter), GET_RTX_NAME (code), > > - (unsigned HOST_WIDE_INT)const_op, GET_RTX_NAME > > (adjusted_code), > > - n); > > + (unsigned HOST_WIDE_INT) const_op & GET_MODE_MASK > > (int_mode), > > + GET_RTX_NAME (adjusted_code), n); > > } > > poly_int64 offset = (BYTES_BIG_ENDIAN > > ? 0 > > : (GET_MODE_SIZE (int_mode) > > - GET_MODE_SIZE (narrow_mode_iter))); > > *pop0 = adjust_address_nv (op0, narrow_mode_iter, offset); > > - *pop1 = GEN_INT (n); > > + *pop1 = gen_int_mode (n, narrow_mode_iter); > > return adjusted_code; > > } > > } > > -- > > 2.41.0 > >
-- Xi Ruoyao <xry...@xry111.site> School of Aerospace Science and Technology, Xidian University