https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112531
Bug ID: 112531 Summary: [14] RISC-V: gcc.dg/unroll-8.c rtl-dump scan errors with --param=riscv-autovec-preference=scalable Product: gcc Version: 14.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: target Assignee: unassigned at gcc dot gnu.org Reporter: ewlu at rivosinc dot com Target Milestone: --- As reported in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111311#c8 The following errors are found on trunk === gcc: Unexpected fails for rv64gcv lp64d medlow === FAIL: gcc.dg/unroll-8.c scan-rtl-dump loop2_unroll "Not unrolling loop, doesn't roll" FAIL: gcc.dg/unroll-8.c scan-rtl-dump loop2_unroll "likely upper bound: 6" FAIL: gcc.dg/unroll-8.c scan-rtl-dump loop2_unroll "realistic bound: -1" I have bisected it down to this commit r14-701-gb75c9e10379 introducing the errors. I have isolated the cause to specifically the change in the expand pass by running the testsuite with just the refactor (reverting the change to autovec.md) and saw no change in testsuite results. Compilation command: ./build-gcc-linux-stage2/gcc/xgcc -B./build-gcc-linux-stage2/gcc/ /scratch/ewlu/ci/triage/baseline/gcc/gcc/testsuite/gcc.dg/unroll-8.c -march=rv64gcv -mabi=lp64d -mcmodel=medlow -fdiagnostics-plain-output -O2 -fdump-rtl-loop2_unroll-details-blocks -funroll-loops -ffat-lto-objects -S -o unroll-8.s --param=riscv-autovec-preference=scalable --fdump-rtl-all --fdump-tree-all Observations: Adding the new define expand pattern changes unroll-8.s to output vector instructions. Previously only scalar output was generated (previous commit: r14-700-gaf595613acb.) The first difference in dump file outputs occurs with the tree dump 172t.vect where vector variables are added. This is confusing to me since I expected the first change to be with the rtl expand pass. I believe this may be the cause of the problem since the optimized tree dump has # loop_len_16 = PHI <_31(4), _27(3)> which affects the analysis of the operands in the loop2_unroll pass. Analyzing operand (reg:DI 137 [ loop_len_16 ]) of insn (jump_insn 56 54 81 10 (set (pc) (if_then_else (ne (reg:DI 137 [ loop_len_16 ]) (const_int 0 [0])) (label_ref:DI 81) (pc))) 242 {*branchdi} (int_list:REG_BR_PROB 894784862 (nil)) -> 81) Checking get reaching def has more than one reaching def not simple. loop number: 1 Failed to analyze op0: (reg:DI 137 [ loop_len_16 ]) Loop 1 is not simple. /scratch/ewlu/ci/triage/baseline/gcc/gcc/testsuite/gcc.dg/unroll-8.c:8:9: note: considering unrolling loop 1 at BB 6 ;; Not unrolling loop, user didn't want it unrolled starting the processing of deferred insns loop_len_16 now has multiple reaching definitions since it is the output of a phi function.