Okay, I'm now trying to reproduce the emitted assembly code,
so I can test whether my change will actually be working or not,
but I had GCC tell me that -march=armv9.5-a is a bad option.
I figured this was because I had built a gcc capable of targeting
x86, not ARM, so I tried bootstrapping a cross compiler for
ARM from current trunk sources after Claude gave me some
setup instructions, but it didn't work. I looked on the GNU
webpages but I couldn't find exact instructions for this either.
I'm doing this on an x86_64 laptop running Fedora natively.
The steps from Claude that I tried:
sudo dnf -y install sysroot-aarch64-fc$(rpm -E %fedora)-glibc
sudo dnf -y install binutils-aarch64-linux-gnu
Then from my build directory separate from the source dir:
../gcc/configure \
--target=aarch64-linux-gnu \
--prefix=$HOME/GCC-CLONED-ARM \
--with-sysroot=/usr/aarch64-redhat-linux/sys-root/fc44 \
--enable-languages=all \
--disable-multilib
This generates a Makefile all good, but then "make" fails
after a while. Is there any hope to set this cross compiler
testing on my x64 laptop or do I have to get on one of the
aarch64 farm machines and test my changes on it?
On Thu, Sep 17, 2026 at 10:11 PM Andrea Pinski
<[email protected]> wrote:
>
> On Thu, Sep 17, 2026 at 11:51 AM Kevin Stefanov
> <[email protected]> wrote:
> >
> > Hi all,
> >
> > I got assigned Easy Issue of Week 52 a while back and have now
> > started digging in.
> >
> > After looking around in simplify-rtx.cc for a while, I believe the
> > code for this simplification should be added under the "case SMAX:"
> > switch case, before the simplify_associative_operation call on
> > line 5038, correct?
>
> Hi Kevin,
> First off thanks for taking a stab at a rtl change.
> Yes that is the correct location where this matching/simplification
> would be placed.
>
> >
> > Also, could somebody point me to some example code I could have a
> > look at, that would help me understand how the check for operand
> > pattern (a, -a) and the operation's actual conversion to abs(a)
> > would look like?
>
> At the very beginning of the
> simplify_context::simplify_binary_operation_1 function, there is one
> for PLUS and conversion to NEG:
> /* (~a) + 1 -> -a */
> if (INTEGRAL_MODE_P (mode)
> && GET_CODE (op0) == NOT
> && trueop1 == const1_rtx)
> return simplify_gen_unary (NEG, mode, XEXP (op0, 0), mode);
> Which can be used as a model. The only thing is you want to use
> rtx_equal_p to compare if 2 rtls are the same (see below for an
> example).
>
> > Perhaps something along the lines of
> > "return gen_rtx_ABS(int_mode, op1)" ?
>
> So for RTL, the operands in this function would be op1 and op0. You
> need to first check if one of them is an NEG RTL and then check if the
> first operand of that is the same as the other original operand.
> To get the operand of a NEG, you use XEXP. The index is the saying
> (in this case) the first operand of NEG.
> So something like:
> if (GET_CODE (op0) == NEG && rtx_equal_p (XEXP (op0, 0), op1))
>
> Also you need to check for an integer mode here since SMAX can be used
> with floating point as described in rtl.def:
> ```
> The signed variants should be used
> with floating point. Further, if both operands are zeros, or if either
> operand is NaN, then it is unspecified which of the two operands is
> returned as the result. */
> ```
> The check would be using INTEGRAL_MODE_P (see machine-mode.h) on the
> mode argument.
>
> And then you need to generate ABS:
> The easiest way is to use simplify_gen_unary:
> simplify_gen_unary (ABS, mode, op1, mode);
>
> And then you need to do the same for the swapped operands snice it is
> symmetrical.
>
>
> >
> > Bugzilla page:
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126726
> >
> > Kev
