[Lldb-commits] [clang] [libcxx] [lldb] [llvm] [mlir] [BOLT][BAT] Add entries for deleted basic blocks (PR #91906)
rafaelauler wrote: Oh I see, thanks! https://github.com/llvm/llvm-project/pull/91906 ___ lldb-commits mailing list lldb-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-commits
[Lldb-commits] [clang] [libcxx] [lldb] [llvm] [mlir] [BOLT][BAT] Add entries for deleted basic blocks (PR #91906)
aaupov wrote: The entries for deleted basic blocks won't participate in `BAT::getFallthroughsInTrace` because trace boundary is looked up by output offsets: https://github.com/llvm/llvm-project/blob/098c6dfa8157681699a71fce9e3d94515e66311f/bolt/lib/Profile/BoltAddressTranslation.cpp#L529-L540 But deleted blocks will be used in `writeBATYAML` where we lookup containing blocks by input offsets: https://github.com/llvm/llvm-project/blob/098c6dfa8157681699a71fce9e3d94515e66311f/bolt/lib/Profile/DataAggregator.cpp#L2358-L2367 https://github.com/llvm/llvm-project/pull/91906 ___ lldb-commits mailing list lldb-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-commits
[Lldb-commits] [clang] [libcxx] [lldb] [llvm] [mlir] [BOLT][BAT] Add entries for deleted basic blocks (PR #91906)
rafaelauler wrote: Thanks for the detailed explanation. So essentially the output offset is not important because these deleted blocks are only useful for their input offset, which will be used in BoltAddressTranslation::getFallthroughsInTrace() to create traffic in this to-be deleted block, is that right? https://github.com/llvm/llvm-project/pull/91906 ___ lldb-commits mailing list lldb-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-commits
[Lldb-commits] [clang] [libcxx] [lldb] [llvm] [mlir] [BOLT][BAT] Add entries for deleted basic blocks (PR #91906)
https://github.com/aaupov closed https://github.com/llvm/llvm-project/pull/91906 ___ lldb-commits mailing list lldb-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-commits
[Lldb-commits] [clang] [libcxx] [lldb] [llvm] [mlir] [BOLT][BAT] Add entries for deleted basic blocks (PR #91906)
aaupov wrote: > Could you elaborate a bit better on why do we need a deleted block to be > present in the table? My memory fails me, aren't we using the translation > table just to map samples collected on the bolted binary? Where do the > deleted blocks become a problem? > > Other than the motivation, the implementation itself looks good to me. We need deleted blocks to correctly map optimized tail calls to containing basic blocks. Because we expand tail calls during CFG construction, and attach the profile to that CFG, we need those intermediate blocks to be present in the profile. bb -with-two-tail-calls offers a good example: after building CFG (details omitted): ``` .LBB00 (1 instructions, align : 1) : je .Ltmp0 # Offset: 0 .LFT0 (2 instructions, align : 1) 0002: ja .Ltmp1 # Offset: 2 0004: jmp .Ltmp2 # Offset: 4 .Ltmp0 (1 instructions, align : 1) 0006: retq # Offset: 6 .Ltmp1 (1 instructions, align : 1) 0007: jmp e # TAILCALL # Offset: 7 .Ltmp2 (2 instructions, align : 1) 000c: nop # Offset: 12 # Size: 1 # NOP: 1 000d: jmp f # TAILCALL # Offset: 13 ``` after SCTC, we normally write out BAT from that state: ``` .LBB00 (1 instructions, align : 1) : je .Ltmp0 # Offset: 0 .LFT0 (2 instructions, align : 1) 0002: ja e # TAILCALL # Offset: 7 # CTCTakenCount: 4 0004: jmp f # TAILCALL # Offset: 13 .Ltmp0 (1 instructions, align : 1) 0009: retq # Offset: 6 ``` So in order to map this branch ``` 0004: jmp f # TAILCALL # Offset: 13 ``` to its block Ltmp2 we need to preserve the block entry in BAT, although it's removed from CFG. https://github.com/llvm/llvm-project/pull/91906 ___ lldb-commits mailing list lldb-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-commits
[Lldb-commits] [clang] [libcxx] [lldb] [llvm] [mlir] [BOLT][BAT] Add entries for deleted basic blocks (PR #91906)
https://github.com/rafaelauler approved this pull request. Could you elaborate a bit better on why do we need a deleted block to be present in the table? My memory fails me, aren't we using the translation table just to map samples collected on the bolted binary? Where do the deleted blocks become a problem? Other than the motivation, the implementation itself looks good to me. https://github.com/llvm/llvm-project/pull/91906 ___ lldb-commits mailing list lldb-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-commits
[Lldb-commits] [clang] [libcxx] [lldb] [llvm] [mlir] [BOLT][BAT] Add entries for deleted basic blocks (PR #91906)
https://github.com/aaupov edited https://github.com/llvm/llvm-project/pull/91906 ___ lldb-commits mailing list lldb-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-commits
