arm: Improve handling of relocations with small offsets with -mpure-code on v6m (PR96770)
With -mpure-code on v6m (thumb-1), we can use small offsets with
upper/lower relocations to avoid the extra addition of the
offset.
This patch accepts expressions symbol+offset as legitimate constants
when the literal pool is disabled, making sure that the offset is
within the range supported by thumb-1 [0..255] as described in the
AAELF32 documentation.
It also makes sure that thumb1_movsi_insn emits an error in case we
try to use it with an unsupported RTL construct.
gcc/
PR target/96770
* config/arm/arm.c (thumb_legitimate_constant_p): Accept
(symbol_ref + addend) when literal pool is disabled.
(arm_valid_symbolic_address_p): Add support for thumb-1 without
MOVT/MOVW.
* config/arm/thumb1.md (*thumb1_movsi_insn): Accept (symbol_ref +
addend) in the pure-code alternative.
gcc/testsuite/
PR target/96770
* gcc.target/arm/pure-code/pr96770.c: New test.