0aa6df6575
This is a resurrection of D106421 with the change that it keeps backward-compatibility. This means decoding the previous version of `LLVM_BB_ADDR_MAP` will work. This is required as the profile mapping tool is not released with LLVM (AutoFDO). As suggested by @jhenderson we rename the original section type value to `SHT_LLVM_BB_ADDR_MAP_V0` and assign a new value to the `SHT_LLVM_BB_ADDR_MAP` section type. The new encoding adds a version byte to each function entry to specify the encoding version for that function. This patch also adds a feature byte to be used with more flexibility in the future. An use-case example for the feature field is encoding multi-section functions more concisely using a different format. Conceptually, the new encoding emits basic block offsets and sizes as label differences between each two consecutive basic block begin and end label. When decoding, offsets must be aggregated along with basic block sizes to calculate the final offsets of basic blocks relative to the function address. This encoding uses smaller values compared to the existing one (offsets relative to function symbol). Smaller values tend to occupy fewer bytes in ULEB128 encoding. As a result, we get about 17% total reduction in the size of the bb-address-map section (from about 11MB to 9MB for the clang PGO binary). The extra two bytes (version and feature fields) incur a small 3% size overhead to the `LLVM_BB_ADDR_MAP` section size. Reviewed By: jhenderson Differential Revision: https://reviews.llvm.org/D121346
42 lines
1.6 KiB
LLVM
42 lines
1.6 KiB
LLVM
; RUN: llc < %s -mtriple=x86_64 -function-sections -basic-block-sections=labels | FileCheck %s
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$_Z4fooTIiET_v = comdat any
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define dso_local i32 @_Z3barv() {
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ret i32 0
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}
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;; Check we add SHF_LINK_ORDER for .llvm_bb_addr_map and link it with the corresponding .text sections.
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; CHECK: .section .text._Z3barv,"ax",@progbits
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; CHECK-LABEL: _Z3barv:
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; CHECK-NEXT: [[BAR_BEGIN:.Lfunc_begin[0-9]+]]:
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; CHECK: .section .llvm_bb_addr_map,"o",@llvm_bb_addr_map,.text._Z3barv{{$}}
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; CHECK-NEXT: .byte 1 # version
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; CHECK-NEXT: .byte 0 # feature
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; CHECK-NEXT: .quad [[BAR_BEGIN]] # function address
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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 .llvm_bb_addr_map,"o",@llvm_bb_addr_map,.text._Z3foov{{$}}
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; CHECK-NEXT: .byte 1 # version
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; CHECK-NEXT: .byte 0 # feature
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; CHECK-NEXT: .quad [[FOO_BEGIN]] # function address
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define linkonce_odr dso_local i32 @_Z4fooTIiET_v() comdat {
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ret i32 0
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}
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;; Check we add .llvm_bb_addr_map section to a COMDAT group with the corresponding .text section if such a COMDAT exists.
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; CHECK: .section .text._Z4fooTIiET_v,"axG",@progbits,_Z4fooTIiET_v,comdat
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; CHECK-LABEL: _Z4fooTIiET_v:
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; CHECK-NEXT: [[FOOCOMDAT_BEGIN:.Lfunc_begin[0-9]+]]:
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; CHECK: .section .llvm_bb_addr_map,"Go",@llvm_bb_addr_map,_Z4fooTIiET_v,comdat,.text._Z4fooTIiET_v{{$}}
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; CHECK-NEXT: .byte 1 # version
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; CHECK-NEXT: .byte 0 # feature
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; CHECK-NEXT: .quad [[FOOCOMDAT_BEGIN]] # function address
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