arm: Avoid indirection with -mpure-code on v6m (PR96967)

With -mpure-code on v6m (thumb-1), to avoid a useless indirection when
building the address of a symbol, we want to consider SYMBOL_REF as a
legitimate constant. This way, we build the address using a series of
upper/lower relocations instead of loading the address from memory.

This patch also fixes a missing "clob" conds attribute for
thumb1_movsi_insn, needed because that alternative clobbers the flags.

2020-11-02  Christophe Lyon  <christophe.lyon@linaro.org>

	gcc/
	PR target/96967
	* config/arm/arm.c (thumb_legitimate_constant_p): Add support for
	disabled literal pool in thumb-1.
	* config/arm/thumb1.md (thumb1_movsi_symbol_ref): Remove.
	(*thumb1_movsi_insn): Add support for SYMBOL_REF with -mpure-code.

	gcc/testsuite
	PR target/96967
	* gcc.target/arm/pure-code/pr96767.c: New test.

3 files changed, 63 insertions, 55 deletions

diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
index dfadaca..d2387c3 100644
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -9500,6 +9500,12 @@ thumb_legitimate_constant_p (machine_mode mode ATTRIBUTE_UNUSED, rtx x)
 	  || CONST_DOUBLE_P (x)
 	  || CONSTANT_ADDRESS_P (x)
 	  || (TARGET_HAVE_MOVT && GET_CODE (x) == SYMBOL_REF)
+	  /* On Thumb-1 without MOVT/MOVW and literal pool disabled,
+	     we build the symbol address with upper/lower
+	     relocations.  */
+	  || (TARGET_THUMB1
+	      && GET_CODE (x) == SYMBOL_REF
+	      && arm_disable_literal_pool)
 	  || flag_pic);
 }
 
diff --git a/gcc/config/arm/thumb1.md b/gcc/config/arm/thumb1.md
index b5377a3..4bf73bf 100644
--- a/gcc/config/arm/thumb1.md
+++ b/gcc/config/arm/thumb1.md
@@ -43,27 +43,6 @@
 
 
 
-(define_insn "thumb1_movsi_symbol_ref"
-  [(set (match_operand:SI 0 "register_operand" "=l")
-	(match_operand:SI 1 "general_operand" ""))
-   ]
-  "TARGET_THUMB1
-   && arm_disable_literal_pool
-   && GET_CODE (operands[1]) == SYMBOL_REF"
-  "*
-  output_asm_insn (\"movs\\t%0, #:upper8_15:%1\", operands);
-  output_asm_insn (\"lsls\\t%0, #8\", operands);
-  output_asm_insn (\"adds\\t%0, #:upper0_7:%1\", operands);
-  output_asm_insn (\"lsls\\t%0, #8\", operands);
-  output_asm_insn (\"adds\\t%0, #:lower8_15:%1\", operands);
-  output_asm_insn (\"lsls\\t%0, #8\", operands);
-  output_asm_insn (\"adds\\t%0, #:lower0_7:%1\", operands);
-  return \"\";
-  "
-  [(set_attr "length" "14")
-   (set_attr "conds" "clob")]
-)
-
 (define_insn "*thumb1_adddi3"
   [(set (match_operand:DI          0 "register_operand" "=l")
 	(plus:DI (match_operand:DI 1 "register_operand" "%0")
@@ -696,40 +675,53 @@
       case 7:
       /* pure-code alternative: build the constant byte by byte,
 	 instead of loading it from a constant pool.  */
-	{
-	  int i;
-	  HOST_WIDE_INT op1 = INTVAL (operands[1]);
-	  bool mov_done_p = false;
-	  rtx ops[2];
-	  ops[0] = operands[0];
-
-	  /* Emit upper 3 bytes if needed.  */
-	  for (i = 0; i < 3; i++)
-	    {
-	       int byte = (op1 >> (8 * (3 - i))) & 0xff;
-
-	      if (byte)
-		{
-		  ops[1] = GEN_INT (byte);
-		  if (mov_done_p)
-		    output_asm_insn ("adds\t%0, %1", ops);
-		  else
-		    output_asm_insn ("movs\t%0, %1", ops);
-		  mov_done_p = true;
-		}
-
-	      if (mov_done_p)
-		output_asm_insn ("lsls\t%0, #8", ops);
-	    }
+	if (GET_CODE (operands[1]) == SYMBOL_REF)
+	  {
+	    output_asm_insn (\"movs\\t%0, #:upper8_15:%1\", operands);
+	    output_asm_insn (\"lsls\\t%0, #8\", operands);
+	    output_asm_insn (\"adds\\t%0, #:upper0_7:%1\", operands);
+	    output_asm_insn (\"lsls\\t%0, #8\", operands);
+	    output_asm_insn (\"adds\\t%0, #:lower8_15:%1\", operands);
+	    output_asm_insn (\"lsls\\t%0, #8\", operands);
+	    output_asm_insn (\"adds\\t%0, #:lower0_7:%1\", operands);
+	    return \"\";
+	  }
+	else
+	  {
+	    int i;
+	    HOST_WIDE_INT op1 = INTVAL (operands[1]);
+	    bool mov_done_p = false;
+	    rtx ops[2];
+	    ops[0] = operands[0];
+
+	    /* Emit upper 3 bytes if needed.  */
+	    for (i = 0; i < 3; i++)
+	      {
+		int byte = (op1 >> (8 * (3 - i))) & 0xff;
+
+		if (byte)
+		  {
+		    ops[1] = GEN_INT (byte);
+		    if (mov_done_p)
+		      output_asm_insn ("adds\t%0, %1", ops);
+		    else
+		      output_asm_insn ("movs\t%0, %1", ops);
+		    mov_done_p = true;
+		  }
+
+		if (mov_done_p)
+		  output_asm_insn ("lsls\t%0, #8", ops);
+	      }
+
+	    /* Emit lower byte if needed.  */
+	    ops[1] = GEN_INT (op1 & 0xff);
+	    if (!mov_done_p)
+	      output_asm_insn ("movs\t%0, %1", ops);
+	    else if (op1 & 0xff)
+	      output_asm_insn ("adds\t%0, %1", ops);
+	    return "";
+	  }
 
-	  /* Emit lower byte if needed.  */
-	  ops[1] = GEN_INT (op1 & 0xff);
-	  if (!mov_done_p)
-	    output_asm_insn ("movs\t%0, %1", ops);
-	  else if (op1 & 0xff)
-	    output_asm_insn ("adds\t%0, %1", ops);
-	  return "";
-	}
       case 8: return "ldr\t%0, %1";
       case 9: return "str\t%1, %0";
       case 10: return "mov\t%0, %1";
@@ -740,7 +732,7 @@
    (set_attr "pool_range" "*,*,*,*,*,*,*, *,1018,*,*")
    (set_attr "arch" "t1,t1,v8mb,t1,t1,t1,t1,t1,t1,t1,t1")
    (set_attr "required_for_purecode" "no,no,no,no,no,no,no,yes,no,no,no")
-   (set_attr "conds" "set,clob,nocond,*,*,nocond,nocond,nocond,nocond,nocond,nocond")])
+   (set_attr "conds" "set,clob,nocond,*,*,nocond,nocond,clob,nocond,nocond,nocond")])
 
 ; Split the load of 64-bit constant into two loads for high and low 32-bit parts respectively
 ; to see if we can load them in fewer instructions or fewer cycles.
diff --git a/gcc/testsuite/gcc.target/arm/pure-code/pr96767.c b/gcc/testsuite/gcc.target/arm/pure-code/pr96767.c
new file mode 100644
index 0000000..cb3ee68
--- /dev/null
+++ b/gcc/testsuite/gcc.target/arm/pure-code/pr96767.c
@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+/* { dg-options "-mpure-code" } */
+
+int x;
+int f1 (void) { return x; }
+
+/* We expect only one indirect load like ldr r3, [r3]. In some
+   configurations there is an additional ldr rX, [sp], #4 which is not
+   related to what we check here, so make sure not to match it.  */
+/* { dg-final { scan-assembler-times "ldr\tr\[0-9\]+, \\\[r\[0-9\]+\\\]" 1 } } */