@@ -9038,17 +9038,20 @@ arm_legitimize_address (rtx x, rtx orig_x, machine_mode mode)
HOST_WIDE_INT mask, base, index;
rtx base_reg;
- /* ldr and ldrb can use a 12-bit index, ldrsb and the rest can only
- use a 8-bit index. So let's use a 12-bit index for SImode only and
- hope that arm_gen_constant will enable ldrb to use more bits. */
+ /* LDR and LDRB can use a 12-bit index, ldrsb and the rest can
+ only use a 8-bit index. So let's use a 12-bit index for
+ SImode only and hope that arm_gen_constant will enable LDRB
+ to use more bits. */
bits = (mode == SImode) ? 12 : 8;
mask = (1 << bits) - 1;
base = INTVAL (x) & ~mask;
index = INTVAL (x) & mask;
- if (bit_count (base & 0xffffffff) > (32 - bits)/2)
- {
- /* It'll most probably be more efficient to generate the base
- with more bits set and use a negative index instead. */
+ if (TARGET_ARM && bit_count (base & 0xffffffff) > (32 - bits)/2)
+ {
+ /* It'll most probably be more efficient to generate the
+ base with more bits set and use a negative index instead.
+ Don't do this for Thumb as negative offsets are much more
+ limited. */
base |= mask;
index -= mask;
}
Thumb2 code now uses the Arm implementation of legitimize_address. That code has a case to handle addresses that are absolute CONST_INT values, which is a common use case in deeply embedded targets (eg: void *p = (void*)0x12345678). Since thumb has very limited negative offsets from a constant, we want to avoid forming a CSE base that will then be used with a negative value. This was reported upstream originally in https://gcc.gnu.org/ml/gcc-help/2019-10/msg00122.html For example, void test1(void) { volatile uint32_t * const p = (uint32_t *) 0x43fe1800; p[3] = 1; p[4] = 2; p[1] = 3; p[7] = 4; p[0] = 6; } With the new code, instead of ldr r3, .L2 subw r2, r3, #2035 movs r1, #1 str r1, [r2] subw r2, r3, #2031 movs r1, #2 str r1, [r2] subw r2, r3, #2043 movs r1, #3 str r1, [r2] subw r2, r3, #2019 movs r1, #4 subw r3, r3, #2047 str r1, [r2] movs r2, #6 str r2, [r3] bx lr We now get ldr r3, .L2 movs r2, #1 str r2, [r3, #2060] movs r2, #2 str r2, [r3, #2064] movs r2, #3 str r2, [r3, #2052] movs r2, #4 str r2, [r3, #2076] movs r2, #6 str r2, [r3, #2048] bx lr * config/arm/arm.c (arm_legitimize_address): Don't form negative offsets from a CONST_INT address when TARGET_THUMB2. Committed.