https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63210
--- Comment #1 from Zhenqiang Chen <zhenqiang.chen at arm dot com> --- Here is a workaround patch to show the point. diff --git a/gcc/ira-color.c b/gcc/ira-color.c index e2ea359..1573fb5 100644 --- a/gcc/ira-color.c +++ b/gcc/ira-color.c @@ -1709,6 +1709,8 @@ assign_hard_reg (ira_allocno_t a, bool retry_p) { ira_allocno_t conflict_a = OBJECT_ALLOCNO (conflict_obj); enum reg_class conflict_aclass; + HARD_REG_SET prof_regs; + prof_regs = ALLOCNO_COLOR_DATA (conflict_a)->profitable_hard_regs; /* Reload can give another class so we need to check all allocnos. */ @@ -1780,7 +1782,7 @@ assign_hard_reg (ira_allocno_t a, bool retry_p) hard_regno = ira_class_hard_regs[aclass][j]; ira_assert (hard_regno >= 0); k = ira_class_hard_reg_index[conflict_aclass][hard_regno]; - if (k < 0) + if (k < 0 || !TEST_HARD_REG_BIT (prof_regs, hard_regno)) continue; full_costs[j] -= conflict_costs[k]; } For this case, "r0" is not available for r115. The conflict for r110 on "r0" maybe meaningless.