https://llvm.org/bugs/show_bug.cgi?id=25612
Bug ID: 25612
Summary: Optimize vadd_s64(vget_low_s64(x), vget_high_s64(x))
as vaddvq_s64(x)
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: enhancement
Priority: P
Component: Backend: AArch64
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
Created attachment 15338
--> https://llvm.org/bugs/attachment.cgi?id=15338&action=edit
Test code with sample functions and test they are identical
On Aarch64, clang/LLVM misses an optimization for vadd_s64(vget_low_s64(x),
vget_high_s64(x)). It can be emitted as addp.2d, in the same way as
vaddvq_s64.
The reason someone would write the former rather than the latter is that the
former is also valid armv7 Neon intrinsic code, whereas the latter is
aarch64-only. (This arose in actual code, Neon optimizations for the Opus
audio codec.)
See attached test code. The two test functions optimize as:
func1:
ext v1.16b, v0.16b, v0.16b, #8
add d0, d0, d1
fmov x0, d0
ret
func2:
addp d0, v0.2d
fmov x0, d0
ret
even though they have identical behavior.
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