[ARM] Add support for -mpure-code in thumb-1 (v6m)
This patch extends support for -mpure-code to all thumb-1 processors,
by removing the need for MOVT.
Symbol addresses are built using upper8_15, upper0_7, lower8_15 and
lower0_7 relocations, and constants are built using sequences of
movs/adds and lsls instructions.
The extension of the *thumb1_movhf pattern uses always the same size
(6) although it can emit a shorter sequence when possible. This is
similar to what *arm32_movhf already does.
CASE_VECTOR_PC_RELATIVE is now false with -mpure-code, to avoid
generating invalid assembly code with differences from symbols from
two different sections (the difference cannot be computed by the
assembler).
Tests pr45701-[12].c needed a small adjustment to avoid matching
upper8_15 when looking for the r8 register.
Test no-literal-pool.c is augmented with __fp16, so it now uses
-mfp16-format=ieee.
Test thumb1-Os-mult.c generates an inline code sequence with
-mpure-code and computes the multiplication by using a sequence of
add/shift rather than using the multiply instruction, so we skip it in
presence of -mpure-code.
With -mcpu=cortex-m0, the pure-code/no-literal-pool.c fails because
code like:
static char *p = "Hello World";
char *
testchar ()
{
return p + 4;
}
generates 2 indirections (I removed non-essential directives/code)
.section .rodata
.LC0:
.ascii "Hello World\000"
.data
p:
.word .LC0
.section .rodata
.LC2:
.word p
.section .text,"0x20000006",%progbits
testchar:
push {r7, lr}
add r7, sp, #0
movs r3, #:upper8_15:#.LC2
lsls r3, #8
adds r3, #:upper0_7:#.LC2
lsls r3, #8
adds r3, #:lower8_15:#.LC2
lsls r3, #8
adds r3, #:lower0_7:#.LC2
ldr r3, [r3]
ldr r3, [r3]
adds r3, r3, #4
movs r0, r3
mov sp, r7
@ sp needed
pop {r7, pc}
By contrast, when using -mcpu=cortex-m4, the code looks like:
.section .rodata
.LC0:
.ascii "Hello World\000"
.data
p:
.word .LC0
testchar:
push {r7}
add r7, sp, #0
movw r3, #:lower16:p
movt r3, #:upper16:p
ldr r3, [r3]
adds r3, r3, #4
mov r0, r3
mov sp, r7
pop {r7}
bx lr
I haven't found yet how to make code for cortex-m0 apply upper/lower
relocations to "p" instead of .LC2. The current code looks functional,
but could be improved.
2019-10-18 Christophe Lyon <email address hidden>
gcc/
* config/arm/arm-protos.h (thumb1_gen_const_int): Add new prototype.
* config/arm/arm.c (arm_option_check_internal): Remove restriction
on MOVT for -mpure-code.
(thumb1_gen_const_int): New function.
(thumb1_legitimate_address_p): Support -mpure-code.
(thumb1_rtx_costs): Likewise.
(thumb1_size_rtx_costs): Likewise.
(arm_thumb1_mi_thunk): Likewise.
* config/arm/arm.h (CASE_VECTOR_PC_RELATIVE): Likewise.
* config/arm/thumb1.md (thumb1_movsi_symbol_ref): New.
(*thumb1_movhf): Support -mpure-code.
gcc/testsuite/
* gcc.target/arm/pr45701-1.c: Adjust for -mpure-code.
* gcc.target/arm/pr45701-2.c: Likewise.
* gcc.target/arm/pure-code/no-literal-pool.c: Add tests for
__fp16.
* gcc.target/arm/pure-code/pure-code.exp: Remove thumb2 and movt
conditions.
* gcc.target/arm/thumb1-Os-mult.c: Skip if -mpure-code is used.
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@279463 138bc75d-0d04-0410-961f-82ee72b054a4
