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xtensa: Defer storing integer constants into litpool until reload

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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 short 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.
This commit is contained in:
Takayuki 'January June' Suwa 2022-06-17 22:47:49 +09:00 • committed by Max Filippov
parent 5a66d7dd2b
commit 479b6f449e
3 changed files with 9 additions and 5 deletions
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6
gcc/config/xtensa/constraints.md
View file

@ -113,8 +113,10 @@
(define_constraint "Y"
"A constant that can be used in relaxed MOVI instructions."
(and (match_code "const_int,const_double,const,symbol_ref,label_ref")
(match_test "TARGET_AUTO_LITPOOLS")))
(ior (and (match_code "const_int,const_double,const,symbol_ref,label_ref")
(match_test "TARGET_AUTO_LITPOOLS"))
(and (match_code "const_int")
(match_test "can_create_pseudo_p ()"))))
;; Memory constraints. Do not use define_memory_constraint here. Doing so
;; causes reload to force some constants into the constant pool, but since

5
gcc/config/xtensa/predicates.md
View file

@ -147,8 +147,9 @@
(match_test "!constantpool_mem_p (op)
|| GET_MODE_SIZE (mode) % UNITS_PER_WORD == 0")))
(ior (and (match_code "const_int")
(match_test "GET_MODE_CLASS (mode) == MODE_INT
&& xtensa_simm12b (INTVAL (op))"))
(match_test "(GET_MODE_CLASS (mode) == MODE_INT
&& xtensa_simm12b (INTVAL (op)))
|| can_create_pseudo_p ()"))
(and (match_code "const_int,const_double,const,symbol_ref,label_ref")
(match_test "(TARGET_CONST16 || TARGET_AUTO_LITPOOLS)
&& CONSTANT_P (op)

3
gcc/config/xtensa/xtensa.cc
View file

@ -1182,7 +1182,8 @@ xtensa_emit_move_sequence (rtx *operands, machine_mode mode)
return 1;
}
if (! TARGET_AUTO_LITPOOLS && ! TARGET_CONST16)
if (! TARGET_AUTO_LITPOOLS && ! TARGET_CONST16
&& ! (CONST_INT_P (src) && can_create_pseudo_p ()))
{
src = force_const_mem (SImode, src);
operands[1] = src;