7841e21c98
This patch introduces the new .bb_addr_map section feature which allows us to emit the bits needed for mapping binary profiles to basic blocks into a separate section. The format of the emitted data is represented as follows. It includes a header for every function: | Address of the function | -> 8 bytes (pointer size) | Number of basic blocks in this function (>0) | -> ULEB128 The header is followed by a BB record for every basic block. These records are ordered in the same order as MachineBasicBlocks are placed in the function. Each BB Info is structured as follows: | Offset of the basic block relative to function begin | -> ULEB128 | Binary size of the basic block | -> ULEB128 | BB metadata | -> ULEB128 [ MBB.isReturn() OR MBB.hasTailCall() << 1 OR MBB.isEHPad() << 2 ] The new feature will replace the existing "BB labels" functionality with -basic-block-sections=labels. The .bb_addr_map section scrubs the specially-encoded BB symbols from the binary and makes it friendly to profilers and debuggers. Furthermore, the new feature reduces the binary size overhead from 70% bloat to only 12%. For more information and results please refer to the RFC: https://lists.llvm.org/pipermail/llvm-dev/2020-July/143512.html Reviewed By: MaskRay, snehasish Differential Revision: https://reviews.llvm.org/D85408
36 lines
1.3 KiB
LLVM
36 lines
1.3 KiB
LLVM
; RUN: llc < %s -mtriple=x86_64 -function-sections -basic-block-sections=labels | FileCheck %s
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$_Z4fooTIiET_v = comdat any
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define dso_local i32 @_Z3barv() {
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ret i32 0
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}
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;; Check we add SHF_LINK_ORDER for .bb_addr_map and link it with the corresponding .text sections.
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; CHECK: .section .text._Z3barv,"ax",@progbits
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; CHECK-LABEL: _Z3barv:
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; CHECK-NEXT: [[BAR_BEGIN:.Lfunc_begin[0-9]+]]:
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; CHECK: .section .bb_addr_map,"o",@progbits,.text._Z3barv{{$}}
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; CHECK-NEXT: .quad [[BAR_BEGIN]]
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define dso_local i32 @_Z3foov() {
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%1 = call i32 @_Z4fooTIiET_v()
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ret i32 %1
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}
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; CHECK: .section .text._Z3foov,"ax",@progbits
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; CHECK-LABEL: _Z3foov:
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; CHECK-NEXT: [[FOO_BEGIN:.Lfunc_begin[0-9]+]]:
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; CHECK: .section .bb_addr_map,"o",@progbits,.text._Z3foov{{$}}
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; CHECK-NEXT: .quad [[FOO_BEGIN]]
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define linkonce_odr dso_local i32 @_Z4fooTIiET_v() comdat {
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ret i32 0
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}
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;; Check we add .bb_addr_map section to a COMDAT group with the corresponding .text section if such a COMDAT exists.
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; CHECK: .section .text._Z4fooTIiET_v,"axG",@progbits,_Z4fooTIiET_v,comdat
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; CHECK-LABEL: _Z4fooTIiET_v:
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; CHECK-NEXT: [[FOOCOMDAT_BEGIN:.Lfunc_begin[0-9]+]]:
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; CHECK: .section .bb_addr_map,"Go",@progbits,_Z4fooTIiET_v,comdat,.text._Z4fooTIiET_v{{$}}
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; CHECK-NEXT: .quad [[FOOCOMDAT_BEGIN]]
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