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* [Bug tree-optimization/102971] New: GCC cannot understand >>32 pattern
@ 2021-10-27 20:29 unlvsur at live dot com
2021-10-27 20:30 ` [Bug tree-optimization/102971] " unlvsur at live dot com
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: unlvsur at live dot com @ 2021-10-27 20:29 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102971
Bug ID: 102971
Summary: GCC cannot understand >>32 pattern
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: unlvsur at live dot com
Target Milestone: ---
https://godbolt.org/z/eeG8fnY1z
I want to seperate a uint_least64_t to 2x uint_least32_t or merge 2x
uint_least32_t to uint_least64_t. GCC just cannot understand the pattern at all
here.
The assembly it generates is very bad for things like this.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/102971] GCC cannot understand >>32 pattern
2021-10-27 20:29 [Bug tree-optimization/102971] New: GCC cannot understand >>32 pattern unlvsur at live dot com
@ 2021-10-27 20:30 ` unlvsur at live dot com
2021-10-27 21:03 ` pinskia at gcc dot gnu.org
2021-10-28 8:19 ` [Bug target/102971] " rguenth at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: unlvsur at live dot com @ 2021-10-27 20:30 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102971
--- Comment #1 from cqwrteur <unlvsur at live dot com> ---
Here is clang
https://godbolt.org/z/7YjW1Ezrx
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/102971] GCC cannot understand >>32 pattern
2021-10-27 20:29 [Bug tree-optimization/102971] New: GCC cannot understand >>32 pattern unlvsur at live dot com
2021-10-27 20:30 ` [Bug tree-optimization/102971] " unlvsur at live dot com
@ 2021-10-27 21:03 ` pinskia at gcc dot gnu.org
2021-10-28 8:19 ` [Bug target/102971] " rguenth at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-10-27 21:03 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102971
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
#include <cstdint>
std::uint64_t umul_naive(std::uint64_t a,std::uint64_t b,std::uint64_t& high)
noexcept
{
std::uint32_t a0(static_cast<std::uint32_t>(a));
std::uint32_t a1(static_cast<std::uint32_t>(a>>32));
std::uint32_t b0(static_cast<std::uint32_t>(b));
std::uint32_t b1(static_cast<std::uint32_t>(b>>32));
std::uint64_t c00(static_cast<std::uint64_t>(a0)*b0);
std::uint64_t c01(static_cast<std::uint64_t>(a0)*b1);
std::uint64_t c10(static_cast<std::uint64_t>(a1)*b0);
std::uint64_t c11(static_cast<std::uint64_t>(a1)*b1);
std::uint64_t d0{static_cast<std::uint32_t>(c00)};
std::uint64_t c00_high{c00>>32};
std::uint64_t c01_low{static_cast<std::uint32_t>(c01)};
std::uint64_t c01_high{c01>>32};
std::uint64_t c10_low{static_cast<std::uint32_t>(c10)};
std::uint64_t c10_high{c10>>32};
std::uint64_t d1{c00_high+c01_low+c10_low};
std::uint64_t d2{(d1>>32)+c10_high+c01_high};
std::uint64_t d3{(d2>>32)+c11};
high=d2|(d3<<32);
return d0|(d1<<32);
}
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug target/102971] GCC cannot understand >>32 pattern
2021-10-27 20:29 [Bug tree-optimization/102971] New: GCC cannot understand >>32 pattern unlvsur at live dot com
2021-10-27 20:30 ` [Bug tree-optimization/102971] " unlvsur at live dot com
2021-10-27 21:03 ` pinskia at gcc dot gnu.org
@ 2021-10-28 8:19 ` rguenth at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: rguenth at gcc dot gnu.org @ 2021-10-28 8:19 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102971
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Component|middle-end |target
Target|i?86 |i?86-*-*
Status|UNCONFIRMED |NEW
Last reconfirmed| |2021-10-28
--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed. With -mno-stv the assembly looks much better so something is wrong
there with costing when deciding to do 64bit math in SSE regs as opposed to
GPR pairs.
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2021-10-28 8:19 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2021-10-27 20:29 [Bug tree-optimization/102971] New: GCC cannot understand >>32 pattern unlvsur at live dot com
2021-10-27 20:30 ` [Bug tree-optimization/102971] " unlvsur at live dot com
2021-10-27 21:03 ` pinskia at gcc dot gnu.org
2021-10-28 8:19 ` [Bug target/102971] " rguenth at gcc dot gnu.org
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