https://gcc.gnu.org/g:c80ac3cb559f6ea2be6be3d0458c1615ff27c9a0
commit r17-3009-gc80ac3cb559f6ea2be6be3d0458c1615ff27c9a0 Author: Kito Cheng <[email protected]> Date: Tue Aug 4 10:43:37 2026 +0800 RISC-V: Don't let popretz combine across a call [PR target/126454] The popretz pass scans backwards from cm.popret for the "li a0, 0" that feeds the (use a0), but nothing stopped the scan at a call: the argument registers of a call live in CALL_INSN_FUNCTION_USAGE, which reg_referenced_p does not look at, and the a0 set by a call_value hides in a PARALLEL, which the bare SET test did not match. A "li a0, 0" that sets up the first argument of a call was therefore deleted and cm.popret became cm.popretz, so the callee got garbage in a0 and the caller returned 0 instead of the result of the callee. Use insn level helpers instead, find_reg_fusage for the uses and reg_set_p for the definitions, and ask them about the word_mode a0 rather than about the a0 of the (use a0), whose mode covers a0 and a1 for a DImode return value on rv32. gcc/ChangeLog: PR target/126454 * config/riscv/riscv-opt-popretz.cc (pass_combine_popretz::execute): Stop the backward scan at any use or definition of a0, including those hidden in CALL_INSN_FUNCTION_USAGE or in a PARALLEL. gcc/testsuite/ChangeLog: PR target/126454 * gcc.target/riscv/pr126454.c: New test. Diff: --- gcc/config/riscv/riscv-opt-popretz.cc | 44 ++++++++++++++++++------------- gcc/testsuite/gcc.target/riscv/pr126454.c | 36 +++++++++++++++++++++++++ 2 files changed, 61 insertions(+), 19 deletions(-) diff --git a/gcc/config/riscv/riscv-opt-popretz.cc b/gcc/config/riscv/riscv-opt-popretz.cc index a109780417b1..3c501d3df239 100644 --- a/gcc/config/riscv/riscv-opt-popretz.cc +++ b/gcc/config/riscv/riscv-opt-popretz.cc @@ -205,7 +205,7 @@ pass_combine_popretz::execute (function *fn) rtx_insn *def_a0_insn = NULL; rtx_insn *use_a0_insn = NULL; - rtx a0_reg = NULL; + rtx a0_reg = regno_reg_rtx[A0_REGNUM]; /* Scan backwards from popret to find the pattern: 1. First, find the (use a0) pseudo-instruction 2. Continue scanning to find "li a0, 0" (set a0 to const0_rtx) @@ -223,29 +223,35 @@ pass_combine_popretz::execute (function *fn) && REG_P (XEXP (def_pat, 0)) && REGNO (XEXP (def_pat, 0)) == A0_REGNUM) { - a0_reg = XEXP (def_pat, 0); use_a0_insn = def_insn; continue; } - if (use_a0_insn && reg_referenced_p (a0_reg, def_pat)) + if (use_a0_insn) { - /* a0 is used by other instruction before its use in popret. */ - use_a0_insn = NULL; - break; - } - - if (use_a0_insn - && GET_CODE (def_pat) == SET - && REG_P (SET_DEST (def_pat)) - && REGNO (SET_DEST (def_pat)) == A0_REGNUM) - { - if (SET_SRC (def_pat) == CONST0_RTX (GET_MODE (SET_SRC (def_pat)))) - def_a0_insn = def_insn; - /* Stop the search regardless of the value assigned to a0, - because we only want to match the last (most recent) - definition of a0 before the (use a0). */ - break; + if (reg_referenced_p (a0_reg, def_pat) + || (CALL_P (def_insn) + && find_reg_fusage (def_insn, USE, a0_reg))) + { + /* a0 is used by other instruction before its use in + popret. */ + use_a0_insn = NULL; + break; + } + + if (reg_set_p (a0_reg, def_insn)) + { + rtx set = single_set (def_insn); + if (set + && REG_P (SET_DEST (set)) + && REGNO (SET_DEST (set)) == A0_REGNUM + && SET_SRC (set) == CONST0_RTX (GET_MODE (SET_SRC (set)))) + def_a0_insn = def_insn; + /* Stop the search regardless of the value assigned to a0, + because we only want to match the last (most recent) + definition of a0 before the (use a0). */ + break; + } } } diff --git a/gcc/testsuite/gcc.target/riscv/pr126454.c b/gcc/testsuite/gcc.target/riscv/pr126454.c new file mode 100644 index 000000000000..ac30c1756dff --- /dev/null +++ b/gcc/testsuite/gcc.target/riscv/pr126454.c @@ -0,0 +1,36 @@ +/* { dg-do compile } */ +/* { dg-options " -Os -march=rv32ima_zca_zcmp -mabi=ilp32 -mcmodel=medlow" }*/ +/* { dg-skip-if "" { *-*-* } {"-O0" "-O1" "-O2" "-Og" "-O3" "-Oz" "-flto"} } */ +/* { dg-final { check-function-bodies "**" "" } } */ + +int callee (int a, int *p); + +/* +**test_arg_setup: +** ... +** li a0,0 +** call callee(?:@plt)? +** cm.popret {ra}, 32 +** ... +*/ +int +test_arg_setup (int mode) +{ + int local = mode; + return callee (0, &local); +} + +/* +**test_ret_zero: +** ... +** call callee(?:@plt)? +** cm.popretz {ra}, 32 +** ... +*/ +int +test_ret_zero (int mode) +{ + int local = mode; + callee (0, &local); + return 0; +}
