diff options
Diffstat (limited to 'gcc/cse.cc')
| -rw-r--r-- | gcc/cse.cc | 15 |
1 files changed, 13 insertions, 2 deletions
@@ -6762,7 +6762,18 @@ cse_main (rtx_insn *f ATTRIBUTE_UNUSED, int nregs) modify the liveness of DEST. DEST is set to pc_rtx for a trapping insn, or for an insn with side effects. We must then count uses of a SET_DEST regardless, because the insn can't be - deleted here. */ + deleted here. + Also count uses of a SET_DEST if it has been used by an earlier insn, + but in that case only when incrementing and not when decrementing, effectively + making setters of such a pseudo non-eliminable. This is for cases like + (set (reg x) (expr)) + ... + (set (reg y) (expr (reg (x)))) + ... + (set (reg x) (expr (reg (x)))) + where we can't eliminate the last insn because x is is still used, if y + is unused we can eliminate the middle insn and when considering the first insn + we used to eliminate it despite it being used in the last insn. */ static void count_reg_usage (rtx x, int *counts, rtx dest, int incr) @@ -6778,7 +6789,7 @@ count_reg_usage (rtx x, int *counts, rtx dest, int incr) switch (code = GET_CODE (x)) { case REG: - if (x != dest) + if (x != dest || (incr > 0 && counts[REGNO (x)])) counts[REGNO (x)] += incr; return; |