Subject: [PATCH 2/2] AArch64: use stable sorting in generating ldp/stp In some corner cases, we have code as below: [base + 0x310] = A [base + 0x320] = B [base + 0x330] = C [base + 0x320] = D unstable sorting could result in wrong value in offset 0x320. The patch fixes it by using gcc_stablesort. 2021-07-14 Bin Cheng * config/aarch64/aarch64.c (aarch64_gen_adjusted_ldpstp): use gcc_stablesort. --- gcc/config/aarch64/aarch64.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c index f5b25a7f704..29d63330951 100644 --- a/gcc/config/aarch64/aarch64.c +++ b/gcc/config/aarch64/aarch64.c @@ -24441,8 +24441,16 @@ aarch64_gen_adjusted_ldpstp (rtx *operands, bool load, for (int i = 0; i < 8; i ++) temp_operands[i] = operands[i]; - /* Sort the operands. */ - qsort (temp_operands, 4, 2 * sizeof (rtx *), aarch64_ldrstr_offset_compare); + /* Sort the operands. Note for cases as below: + [base + 0x310] = A + [base + 0x320] = B + [base + 0x330] = C + [base + 0x320] = D + We need stable sorting otherwise wrong data may be store to offset 0x320. + Also note the dead store in above case should be optimized away, but no + guarantees here. */ + gcc_stablesort(temp_operands, 4, 2 * sizeof (rtx *), + aarch64_ldrstr_offset_compare); /* Copy the memory operands so that if we have to bail for some reason the original addresses are unchanged. */ -- 2.19.1.6.gb485710b