erratum:
- extern unsigned int value;
+ extern unsigned short value;
On 2022/06/17 22:47, Takayuki 'January June' Suwa via Gcc-patches wrote:
> Storing integer constants into litpool in the early stage of compilation
> hinders some integer optimizations. In fact, such integer constants are
> not subject to the constant folding process.
>
> For example:
>
> extern unsigned int value;
> extern void foo(void);
> void test(void) {
> if (value == 30001)
> foo();
> }
>
> .literal_position
> .literal .LC0, value
> .literal .LC1, 30001
> test:
> l32r a3, .LC0
> l32r a2, .LC1
> l16ui a3, a3, 0
> extui a2, a2, 0, 16 // runtime zero-extension despite constant
> bne a3, a2, .L1
> j.l foo, a9
> .L1:
> ret.n
>
> This patch defers the placement of integer constants into litpool until
> the start of reload:
>
> .literal_position
> .literal .LC0, value
> .literal .LC1, 30001
> test:
> l32r a3, .LC0
> l32r a2, .LC1
> l16ui a3, a3, 0
> bne a3, a2, .L1
> j.l foo, a9
> .L1:
> ret.n
>
> gcc/ChangeLog:
>
> * config/xtensa/constraints.md (Y):
> Change to include integer constants until reload begins.
> * config/xtensa/predicates.md (move_operand): Ditto.
> * config/xtensa/xtensa.cc (xtensa_emit_move_sequence):
> Change to allow storing integer constants into litpool only after
> reload begins.
