84afdb4771
`ConcatInputSection::foldIdentical()` clears the folded functions `originalUnwindEntry`. However, it cleared every symbol: with N members, the repeated clearing is **O(N²)**. This is redundant: we should only remove the incoming `copy->symbols`. This patch moves the removing loop ahead and adds more clear comments on why we need to skip the first element. Also added a new `lld/test/MachO/icf-scale-same-class.s` with 500K identical functions as a stress test, which would've taken minutes to link, and less than a second with the patch. Testing on real-world app (IRPGO instrumentation + ICF) find that we achieved a 19x speed up (1:14:42 -> 3:55)
37 lines
1 KiB
ArmAsm
37 lines
1 KiB
ArmAsm
# REQUIRES: x86
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# RUN: rm -rf %t*
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# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t.o
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# RUN: %lld -lSystem --icf=all -o %t %t.o
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# RUN: llvm-objdump --macho --section-headers %t | FileCheck %s --check-prefix=SECT
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# RUN: llvm-objdump --macho --syms %t | FileCheck %s --check-prefix=SYMS
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## Every body folds into one, so __text holds a single 6-byte body plus _main
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## rather than the 3 MiB (0x30000d) the unfolded copies occupy.
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# SECT: Idx Name Size
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# SECT-NEXT: 0 __text 00000009
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## The sentinels bracket the group, so checking that the first and last members
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## of the class share an address covers the whole run of folds.
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# SYMS-DAG: [[#%.16x,F:]] g F __TEXT,__text _f_first
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# SYMS-DAG: [[#F]] g F __TEXT,__text _f_last
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.subsections_via_symbols
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.text
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.p2align 2
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.globl _f_first
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_f_first:; movl $7, %eax; ret
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## 64 Ki identical function landing in one equivalence class.
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.rept 65536
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.globl _f\+
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_f\+:; movl $$7, %eax; ret
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.endr
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.globl _f_last
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_f_last:; movl $7, %eax; ret
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.globl _main
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_main:
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ret
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