arm: Improve immediate generation for thumb-1 with -mpurecode [PR96769]

This patch moves the move-immediate splitter after the regular ones so
that it has lower precedence, and updates its constraints.

For
int f3 (void) { return 0x11000000; }
int f3_2 (void) { return 0x12345678; }

we now generate:
* with -O2 -mcpu=cortex-m0 -mpure-code:
f3:
	movs    r0, #136
	lsls    r0, r0, #21
	bx      lr
f3_2:
	movs    r0, #18
	lsls    r0, r0, #8
	adds    r0, r0, gcc-mirror#52
	lsls    r0, r0, #8
	adds    r0, r0, gcc-mirror#86
	lsls    r0, r0, #8
	adds    r0, r0, #121
	bx      lr

* with -O2 -mcpu=cortex-m23 -mpure-code:
f3:
	movs    r0, #136
	lsls    r0, r0, #21
	bx      lr
f3_2:
	movw    r0, #22136
	movt    r0, 4660
	bx      lr

2020-09-04  Christophe Lyon  <[email protected]>

	PR target/96769
	gcc/
	* config/arm/thumb1.md: Move movsi splitter for
	arm_disable_literal_pool after the other movsi splitters.

	gcc/testsuite/
	* gcc.target/arm/pure-code/pr96769.c: New test.

gcc/config/arm/thumb1.md

@@ -64,21 +64,6 @@
    (set_attr "conds" "clob")]
 )
 
-(define_split
-  [(set (match_operand:SI 0 "register_operand" "")
-	(match_operand:SI 1 "immediate_operand" ""))]
-  "TARGET_THUMB1
-   && arm_disable_literal_pool
-   && GET_CODE (operands[1]) == CONST_INT
-   && !TARGET_HAVE_MOVT
-   && !satisfies_constraint_I (operands[1])"
-  [(clobber (const_int 0))]
-  "
-    thumb1_gen_const_int (operands[0], INTVAL (operands[1]));
-    DONE;
-  "
-)
-
 (define_insn "*thumb1_adddi3"
   [(set (match_operand:DI          0 "register_operand" "=l")
 	(plus:DI (match_operand:DI 1 "register_operand" "%0")
@@ -832,6 +817,21 @@
   }"
 )
 
+(define_split
+  [(set (match_operand:SI 0 "register_operand" "")
+	(match_operand:SI 1 "const_int_operand" ""))]
+  "TARGET_THUMB1
+   && arm_disable_literal_pool
+   && GET_CODE (operands[1]) == CONST_INT
+   && !TARGET_HAVE_MOVT
+   && !satisfies_constraint_K (operands[1])"
+  [(clobber (const_int 0))]
+  "
+    thumb1_gen_const_int (operands[0], INTVAL (operands[1]));
+    DONE;
+  "
+)
+
 (define_insn "*thumb1_movhi_insn"
   [(set (match_operand:HI 0 "nonimmediate_operand" "=l,l,m,l*r,*h,l,r")
 	(match_operand:HI 1 "general_operand"       "l,m,l,k*h,*r,I,n"))]

gcc/testsuite/gcc.target/arm/pure-code/pr96769.c

@@ -0,0 +1,20 @@
+/* { dg-do compile } */
+/* { dg-options "-mpure-code" } */
+
+int f3 (void) { return 0x11000000; }
+int f3_2 (void) { return 0x12345678; }
+int f3_3 (void) { return -1; }
+int f3_4 (void) { return 511; }
+
+/* For cortex-m0 (thumb-1/v6m), we generate 1 lsls in f3 3 lsls in f3_2 and 1 in f3_4; 1 rsbs in f3_3.  */
+/* { dg-final { scan-assembler-times "lsls" 5 { target { { ! arm_thumb1_movt_ok } && { ! arm_thumb2_ok } } } } } */
+/* { dg-final { scan-assembler-times "rsbs" 1 { target { { ! arm_thumb1_movt_ok } && { ! arm_thumb2_ok } } } } } */
+
+/* For cortex-m23 (thumb-1/v8m.base), we generate 1 lsls in f3, and none in f3_2 nor f3_4; 1 rsbs in f3_3.  */
+/* { dg-final { scan-assembler-times "lsls" 1 { target { arm_thumb1_movt_ok && { ! arm_thumb2_ok } } } } } */
+/* { dg-final { scan-assembler-times "rsbs" 1 { target { arm_thumb1_movt_ok && { ! arm_thumb2_ok } } } } } */
+
+/* For cortex-m3 (thumb-2/v7m), we generate no lsls and no rsbs.  */
+/* { dg-final { scan-assembler-times "lsls" 0 { target { arm_thumb2_ok } } } } */
+/* { dg-final { scan-assembler-times "rsbs" 0 { target { arm_thumb2_ok } } } } */
+