On Fri, 2020-08-21 at 13:53 +0100, Roger Sayle wrote:
> This patch improves the code generated on PA-RISC for DImode
> (double word) left shifts by small constants (1-31). This target
> has a very cool shd instruction that can be recognized by combine
> for simple shifts, but relying on combine is fragile for more
> complicated functions. This patch tweaks pa.md's ashldi3 expander,
> to form the optimal two instruction shd/zdep sequence at RTL
> expansion time.
>
> As an example of the benefits of this approach, the simple function
>
> unsigned long long u9(unsigned long long x) { return x*9; }
>
> currently generates 9 instructions
>
> u9: copy %r25,%r28
> copy %r26,%r29
> extru %r26,2,3,%r21
> zdep %r25,28,29,%r19
> zdep %r26,28,29,%r20
> or %r21,%r19,%r19
> add %r29,%r20,%r29
> addc %r28,%r19,%r28
> bv,n %r0(%r2)
>
> and with this patch now requires only 7:
>
> u9: copy %r25,%r28
> copy %r26,%r29
> shd %r26,%r25,29,%r19
> zdep %r26,28,29,%r20
> add %r29,%r20,%r29
> addc %r28,%r19,%r28
> bv,n %r0(%r2)
>
>
> This improvement is a first step towards getting synth_mult to
> behave sanely on hppa (PR middle-end/87256).
>
> Unfortunately, it's been a long while since I've had access to a
> hppa system, so apart from building a cross-compiler and looking at
> the assembler it generates, this patch is completely untested.
> I was wondering whether Dave or Jeff (or someone else with access
> to real hardware) might "spin" this patch for me?
So while I have an R390 down in the basement, it overheats and I don't think
I've
turned it on in a few years.
What I do for testing is exploit QEMU user mode emulation. I have a little root
filesystem with HPPA binaries -- there's enough bits in that filesystem to build
binutils, gcc, glibc & the linux kernel as well as run the testsuite.
The root filesystems are here:
https://github.com/JeffreyALaw/chroots
The Jenkins tester spins the PA once week. It failed its last run due to
regressions in the analyzer. I didn't realize it was running the static
analyzer
for the qemu emulated targets, which I turned off yesterday and re-started the
PA
build.
http://3.14.90.209:8080/job/hppa-linux-gnu/
Jeff
>
