https://gcc.gnu.org/g:dcba59a336f5307d577fd3bacae65258447d1803
commit r17-844-gdcba59a336f5307d577fd3bacae65258447d1803 Author: Philipp Tomsich <[email protected]> Date: Fri Mar 20 17:14:00 2026 +0100 ext-dce: fix off-by-one in subreg liveness for 32-bit modes ext_dce_process_uses uses `size >= 32` to decide whether group 3 (bits 32-63) is live for a lowpart subreg source. For SImode subregs (size == 32), this incorrectly marks bits 32-63 as live, preventing the pass from recognizing that the upper half of a DImode register is dead. This blocks lw -> lwu narrowing on RV64. Change the condition to `size > 32`, consistent with the other thresholds in the same block (size > 8, size > 16). The size > 32 case is still reachable via SUBREG_PROMOTED_VAR_P which widens size beyond the outer mode. gcc/ChangeLog: * ext-dce.cc (ext_dce_process_uses): Fix off-by-one: use size > 32 instead of size >= 32 for group 3 liveness. Co-authored-by: Konstantinos Eleftheriou <[email protected]> Diff: --- gcc/ext-dce.cc | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/gcc/ext-dce.cc b/gcc/ext-dce.cc index 9475b18cd344..86457d31af52 100644 --- a/gcc/ext-dce.cc +++ b/gcc/ext-dce.cc @@ -1353,7 +1353,7 @@ ext_dce_process_uses (rtx_insn *insn, rtx obj, bitmap_set_bit (livenow, rn + 1); if (size > 16) bitmap_set_bit (livenow, rn + 2); - if (size >= 32) + if (size > 32) bitmap_set_bit (livenow, rn + 3); iter.skip_subrtxes (); }
