https://bugs.llvm.org/show_bug.cgi?id=51317
Bug ID: 51317
Summary: `and 0xff` on load of 1 byte
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: Backend: AArch64
Assignee: unassignedb...@nondot.org
Reporter: kutdan...@yandex.ru
CC: arnaud.degrandmai...@arm.com,
llvm-bugs@lists.llvm.org, smithp...@googlemail.com,
ties.st...@arm.com
Minimal example https://gcc.godbolt.org/z/z8GrK6v95
DecompressBranchless
ldrb w8, [x0], #1
.LBB0_1: // =>This Inner Loop Header: Depth=1
and x9, x8, #0xff // Redundant!!!!!!!!!
ldrh w11, [x5, x9, lsl #1]
ubfx x10, x8, #2, #6
ands x8, x8, #0x3
csinc x8, x8, x10, ne
add x10, x2, x11
add x9, x0, x8
add x11, x3, x10
ldrb w8, [x9], #1
csel x11, x0, x11, eq
ldrb w11, [x11]
cmp x9, x1
strb w11, [x3, x2]
b.hs .LBB0_3
cmp x10, x4
mov x0, x9
mov x2, x10
b.lt .LBB0_1
.LBB0_3:
ret
After adding `asm("" ::"r"(tag));`, and is removed
DecompressBranchlessBetter
ldrb w8, [x0], #1
.LBB1_1: // =>This Inner Loop Header: Depth=1
ldrh w10, [x5, x8, lsl #1]
lsr x9, x8, #2
ands x8, x8, #0x3
csinc x8, x8, x9, ne
add x10, x2, x10
add x9, x0, x8
add x11, x3, x10
ldrb w8, [x9], #1
csel x11, x0, x11, eq
ldrb w11, [x11]
cmp x9, x1
strb w11, [x3, x2]
b.hs .LBB1_3
cmp x10, x4
mov x0, x9
mov x2, x10
b.lt .LBB1_1
.LBB1_3:
ret
--
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