en Copyright 2015 Java http://src.rcs.uwaterloo.ca:8080/source/history/llvm-project/llvm/test/CodeGen/BPF/CORE/simplify-patchable-liveness-bug.ll#27026fe5633b546ed647efd99eccdfc598686535 [BPF] Reset machine register kill mark in BPFMISimplifyPatchableWhen LLVM is build with `LLVM_ENABLE_EXPENSIVE_CHECKS=ON` optionthe following C code snippet: struct t { unsigned long a; } __attribute__((preserve_access_index)); void foo(volatile struct t *t, volatile unsigned long *p) { *p = t->a; *p = t->a; }Causes an assertion: $ clang -g -O2 -c --target=bpf -mcpu=v2 t2.c -o /dev/null # After BPF PreEmit SimplifyPatchable # Machine code for function foo: IsSSA, TracksLiveness Function Live Ins: $r1 in %0, $r2 in %1 bb.0.entry: liveins: $r1, $r2 DBG_VALUE $r1, $noreg, !"t", !DIExpression() DBG_VALUE $r2, $noreg, !"p", !DIExpression() %1:gpr = COPY $r2 DBG_VALUE %1:gpr, $noreg, !"p", !DIExpression() %0:gpr = COPY $r1 DBG_VALUE %0:gpr, $noreg, !"t", !DIExpression() %2:gpr = LD_imm64 @"llvm.t:0:0$0:0" %4:gpr = ADD_rr %0:gpr(tied-def 0), killed %2:gpr %5:gpr = CORE_LD 344, %0:gpr, @"llvm.t:0:0$0:0" STD killed %5:gpr, %1:gpr, 0 %7:gpr = ADD_rr %0:gpr(tied-def 0), killed %2:gpr %8:gpr = CORE_LD 344, %0:gpr, @"llvm.t:0:0$0:0" STD killed %8:gpr, %1:gpr, 0 RET # End machine code for function foo. *** Bad machine code: Using a killed virtual register *** - function: foo - basic block: %bb.0 entry (0x6210000e6690) - instruction: %7:gpr = ADD_rr %0:gpr(tied-def 0), killed %2:gpr - operand 2: killed %2:gprThis happens because of the wayBPFMISimplifyPatchable::processDstReg() updates second operand of the`ADD_rr` instruction. Code before `BPFMISimplifyPatchable`: .-> %2:gpr = LD_imm64 @"llvm.t:0:0$0:0" | |`----------------. | %3:gpr = LDD %2:gpr, 0 | %4:gpr = ADD_rr %0:gpr(tied-def 0), killed %3:gpr <--- (1) | %5:gpr = LDD killed %4:gpr, 0 ^^^^^^^^^^^^^ | STD killed %5:gpr, %1:gpr, 0 this is updated `----------------. %6:gpr = LDD %2:gpr, 0 %7:gpr = ADD_rr %0:gpr(tied-def 0), killed %6:gpr <--- (2) %8:gpr = LDD killed %7:gpr, 0 ^^^^^^^^^^^^^ STD killed %8:gpr, %1:gpr, 0 this is updatedInstructions (1) and (2) would be updated to: ADD_rr %0:gpr(tied-def 0), killed %2:gprThe `killed` mark is inherited from machine operands `killed %3:gpr`and `killed %6:gpr` which are updated inplace by `processDstReg()`.This commit updates `processDstReg()` reset kill marks for updatedmachine operands to keep liveness information conservatively correct.Differential Revision: https://reviews.llvm.org/D157805 List of files: /llvm-project/llvm/test/CodeGen/BPF/CORE/simplify-patchable-liveness-bug.ll Sun, 13 Aug 2023 00:11:37 +0000 Eduard Zingerman <eddyz87@gmail.com>