LoongArch: Use explicit relocs for addresses only used for one load or store with -mexplicit-relocs=auto and -mcmodel={normal,medium}

In these cases, if we use explicit relocs, we end up with 2
instructions:

    pcalau12i    t0, %pc_hi20(x)
    ld.d         t0, t0, %pc_lo12(x)

If we use la.local pseudo-op, in the best scenario (x is in +/- 2MiB
range) we still have 2 instructions:

    pcaddi       t0, %pcrel_20(x)
    ld.d         t0, t0, 0

If x is out of the range we'll have 3 instructions.  So for these cases
just emit machine instructions with explicit relocs.

gcc/ChangeLog:

	* config/loongarch/predicates.md (symbolic_pcrel_operand): New
	predicate.
	* config/loongarch/loongarch.md (define_peephole2): Optimize
	la.local + ld/st to pcalau12i + ld/st if the address is only used
	once if -mexplicit-relocs=auto and -mcmodel=normal or medium.

gcc/testsuite/ChangeLog:

	* gcc.target/loongarch/explicit-relocs-auto-single-load-store.c:
	New test.
	* gcc.target/loongarch/explicit-relocs-auto-single-load-store-no-anchor.c:
	New test.

4 files changed, 149 insertions, 0 deletions

diff --git a/gcc/config/loongarch/loongarch.md b/gcc/config/loongarch/loongarch.md
index 695c8eb..1347347 100644
--- a/gcc/config/loongarch/loongarch.md
+++ b/gcc/config/loongarch/loongarch.md
@@ -65,6 +65,7 @@
 
   UNSPEC_LOAD_FROM_GOT
   UNSPEC_PCALAU12I
+  UNSPEC_PCALAU12I_GR
   UNSPEC_ORI_L_LO12
   UNSPEC_LUI_L_HI20
   UNSPEC_LUI_H_LO20
@@ -2297,6 +2298,16 @@
   "pcalau12i\t%0,%%pc_hi20(%1)"
   [(set_attr "type" "move")])
 
+;; @pcalau12i may be used for sibcall so it has a strict constraint.  This
+;; allows any general register as the operand.
+(define_insn "@pcalau12i_gr<mode>"
+  [(set (match_operand:P 0 "register_operand" "=r")
+       (unspec:P [(match_operand:P 1 "symbolic_operand" "")]
+       UNSPEC_PCALAU12I_GR))]
+  ""
+  "pcalau12i\t%0,%%pc_hi20(%1)"
+  [(set_attr "type" "move")])
+
 (define_insn "@ori_l_lo12<mode>"
   [(set (match_operand:P 0 "register_operand" "=r")
 	(unspec:P [(match_operand:P 1 "register_operand" "r")
@@ -3748,6 +3759,117 @@
   [(set_attr "type" "unknown")
    (set_attr "mode" "<MODE>")])
 
+;; With normal or medium code models, if the only use of a pc-relative
+;; address is for loading or storing a value, then relying on linker
+;; relaxation is not better than emitting the machine instruction directly.
+;; Even if the la.local pseudo op can be relaxed, we get:
+;;
+;;     pcaddi     $t0, %pcrel_20(x)
+;;     ld.d       $t0, $t0, 0
+;;
+;; There are still two instructions, same as using the machine instructions
+;; and explicit relocs:
+;;
+;;     pcalau12i  $t0, %pc_hi20(x)
+;;     ld.d       $t0, $t0, %pc_lo12(x)
+;;
+;; And if the pseudo op cannot be relaxed, we'll get a worse result (with
+;; 3 instructions).
+(define_peephole2
+  [(set (match_operand:P 0 "register_operand")
+	(match_operand:P 1 "symbolic_pcrel_operand"))
+   (set (match_operand:GPR 2 "register_operand")
+	(mem:GPR (match_dup 0)))]
+  "la_opt_explicit_relocs == EXPLICIT_RELOCS_AUTO \
+   && (TARGET_CMODEL_NORMAL || TARGET_CMODEL_MEDIUM) \
+   && (peep2_reg_dead_p (2, operands[0]) \
+       || REGNO (operands[0]) == REGNO (operands[2]))"
+  [(set (match_dup 2) (mem:GPR (lo_sum:P (match_dup 0) (match_dup 1))))]
+  {
+    emit_insn (gen_pcalau12i_gr<P:mode> (operands[0], operands[1]));
+  })
+
+(define_peephole2
+  [(set (match_operand:P 0 "register_operand")
+	(match_operand:P 1 "symbolic_pcrel_operand"))
+   (set (match_operand:GPR 2 "register_operand")
+	(mem:GPR (plus (match_dup 0)
+		       (match_operand 3 "const_int_operand"))))]
+  "la_opt_explicit_relocs == EXPLICIT_RELOCS_AUTO \
+   && (TARGET_CMODEL_NORMAL || TARGET_CMODEL_MEDIUM) \
+   && (peep2_reg_dead_p (2, operands[0]) \
+       || REGNO (operands[0]) == REGNO (operands[2]))"
+  [(set (match_dup 2) (mem:GPR (lo_sum:P (match_dup 0) (match_dup 1))))]
+  {
+    operands[1] = plus_constant (Pmode, operands[1], INTVAL (operands[3]));
+    emit_insn (gen_pcalau12i_gr<P:mode> (operands[0], operands[1]));
+  })
+
+(define_peephole2
+  [(set (match_operand:P 0 "register_operand")
+	(match_operand:P 1 "symbolic_pcrel_operand"))
+   (set (match_operand:GPR 2 "register_operand")
+	(any_extend:GPR (mem:SUBDI (match_dup 0))))]
+  "la_opt_explicit_relocs == EXPLICIT_RELOCS_AUTO \
+   && (TARGET_CMODEL_NORMAL || TARGET_CMODEL_MEDIUM) \
+   && (peep2_reg_dead_p (2, operands[0]) \
+       || REGNO (operands[0]) == REGNO (operands[2]))"
+  [(set (match_dup 2)
+	(any_extend:GPR (mem:SUBDI (lo_sum:P (match_dup 0)
+					     (match_dup 1)))))]
+  {
+    emit_insn (gen_pcalau12i_gr<P:mode> (operands[0], operands[1]));
+  })
+
+(define_peephole2
+  [(set (match_operand:P 0 "register_operand")
+	(match_operand:P 1 "symbolic_pcrel_operand"))
+   (set (match_operand:GPR 2 "register_operand")
+	(any_extend:GPR
+	  (mem:SUBDI (plus (match_dup 0)
+			   (match_operand 3 "const_int_operand")))))]
+  "la_opt_explicit_relocs == EXPLICIT_RELOCS_AUTO \
+   && (TARGET_CMODEL_NORMAL || TARGET_CMODEL_MEDIUM) \
+   && (peep2_reg_dead_p (2, operands[0]) \
+       || REGNO (operands[0]) == REGNO (operands[2]))"
+  [(set (match_dup 2)
+	(any_extend:GPR (mem:SUBDI (lo_sum:P (match_dup 0)
+					     (match_dup 1)))))]
+  {
+    operands[1] = plus_constant (Pmode, operands[1], INTVAL (operands[3]));
+    emit_insn (gen_pcalau12i_gr<P:mode> (operands[0], operands[1]));
+  })
+
+(define_peephole2
+  [(set (match_operand:P 0 "register_operand")
+	(match_operand:P 1 "symbolic_pcrel_operand"))
+   (set (mem:QHWD (match_dup 0))
+	(match_operand:QHWD 2 "register_operand"))]
+  "la_opt_explicit_relocs == EXPLICIT_RELOCS_AUTO \
+   && (TARGET_CMODEL_NORMAL || TARGET_CMODEL_MEDIUM) \
+   && (peep2_reg_dead_p (2, operands[0])) \
+   && REGNO (operands[0]) != REGNO (operands[2])"
+  [(set (mem:QHWD (lo_sum:P (match_dup 0) (match_dup 1))) (match_dup 2))]
+  {
+    emit_insn (gen_pcalau12i_gr<P:mode> (operands[0], operands[1]));
+  })
+
+(define_peephole2
+  [(set (match_operand:P 0 "register_operand")
+	(match_operand:P 1 "symbolic_pcrel_operand"))
+   (set (mem:QHWD (plus (match_dup 0)
+			(match_operand 3 "const_int_operand")))
+	(match_operand:QHWD 2 "register_operand"))]
+  "la_opt_explicit_relocs == EXPLICIT_RELOCS_AUTO \
+   && (TARGET_CMODEL_NORMAL || TARGET_CMODEL_MEDIUM) \
+   && (peep2_reg_dead_p (2, operands[0])) \
+   && REGNO (operands[0]) != REGNO (operands[2])"
+  [(set (mem:QHWD (lo_sum:P (match_dup 0) (match_dup 1))) (match_dup 2))]
+  {
+    operands[1] = plus_constant (Pmode, operands[1], INTVAL (operands[3]));
+    emit_insn (gen_pcalau12i_gr<P:mode> (operands[0], operands[1]));
+  })
+
 ;; Synchronization instructions.
 
 (include "sync.md")
diff --git a/gcc/config/loongarch/predicates.md b/gcc/config/loongarch/predicates.md
index 359878f..946ed0d 100644
--- a/gcc/config/loongarch/predicates.md
+++ b/gcc/config/loongarch/predicates.md
@@ -563,6 +563,13 @@
   return loongarch_symbolic_constant_p (op, &type);
 })
 
+(define_predicate "symbolic_pcrel_operand"
+  (match_code "const,symbol_ref,label_ref")
+{
+  enum loongarch_symbol_type type;
+  return loongarch_symbolic_constant_p (op, &type) && type == SYMBOL_PCREL;
+})
+
 (define_predicate "equality_operator"
   (match_code "eq,ne"))
 
diff --git a/gcc/testsuite/gcc.target/loongarch/explicit-relocs-auto-single-load-store-no-anchor.c b/gcc/testsuite/gcc.target/loongarch/explicit-relocs-auto-single-load-store-no-anchor.c
new file mode 100644
index 0000000..fb03403
--- /dev/null
+++ b/gcc/testsuite/gcc.target/loongarch/explicit-relocs-auto-single-load-store-no-anchor.c
@@ -0,0 +1,6 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -march=loongarch64 -mabi=lp64d -mexplicit-relocs=auto -fno-section-anchors" } */
+
+#include "explicit-relocs-auto-single-load-store.c"
+
+/* { dg-final { scan-assembler-not "la.local" } } */
diff --git a/gcc/testsuite/gcc.target/loongarch/explicit-relocs-auto-single-load-store.c b/gcc/testsuite/gcc.target/loongarch/explicit-relocs-auto-single-load-store.c
new file mode 100644
index 0000000..0d53644
--- /dev/null
+++ b/gcc/testsuite/gcc.target/loongarch/explicit-relocs-auto-single-load-store.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -march=loongarch64 -mabi=lp64d -mexplicit-relocs=auto" } */
+
+long a;
+int b;
+unsigned int c;
+
+long load_a() { return a; }
+long load_b() { return b; }
+long load_c() { return c; }
+void store_a(long x) { a = x; }
+void store_b(int x) { b = x; }
+
+/* { dg-final { scan-assembler-not "la.local" } } */