[arm] Avoid STRD with odd register for TARGET_ARM in output_move_double

In this testcase the user forces an odd register as the starting reg for a DFmode value.
The output_move_double function tries to store that using an STRD instruction.
But for TARGET_ARM the starting register of an STRD must be an even one.
This is always the case with compiler-allocated registers for DFmode values, but the
inline assembly forced our hand here.

This patch  restricts the STRD-emitting logic in output_move_double to not avoid
odd-numbered source registers in STRD.
I'm not a fan of the whole function, we should be exposing a lot of the logic in there
to RTL rather than at the final output stage, but that would need to be fixed separately.

	* config/arm/arm.c (output_move_double): Don't allow STRD instructions
	if starting source register is not even.

	* gcc.target/arm/arm-soft-strd-even.c: New test.

From-SVN: r262250

gcc/ChangeLog

+2018-06-29  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
+
+	* config/arm/arm.c (output_move_double): Don't allow STRD instructions
+	if starting source register is not even.
+
 2018-06-29  Martin Liska  <mliska@suse.cz>
 
         PR tree-optimization/86263

gcc/config/arm/arm.c

@@ -18463,12 +18463,18 @@ output_move_double (rtx *operands, bool emit, int *count)
       gcc_assert ((REGNO (operands[1]) != IP_REGNUM)
                   || (TARGET_ARM && TARGET_LDRD));
 
+      /* For TARGET_ARM the first source register of an STRD
+	 must be even.  This is usually the case for double-word
+	 values but user assembly constraints can force an odd
+	 starting register.  */
+      bool allow_strd = TARGET_LDRD
+			 && !(TARGET_ARM && (REGNO (operands[1]) & 1) == 1);
       switch (GET_CODE (XEXP (operands[0], 0)))
         {
 	case REG:
 	  if (emit)
 	    {
-	      if (TARGET_LDRD)
+	      if (allow_strd)
 		output_asm_insn ("strd%?\t%1, [%m0]", operands);
 	      else
 		output_asm_insn ("stm%?\t%m0, %M1", operands);
@@ -18476,7 +18482,7 @@ output_move_double (rtx *operands, bool emit, int *count)
 	  break;
 
         case PRE_INC:
-	  gcc_assert (TARGET_LDRD);
+	  gcc_assert (allow_strd);
 	  if (emit)
 	    output_asm_insn ("strd%?\t%1, [%m0, #8]!", operands);
 	  break;
@@ -18484,7 +18490,7 @@ output_move_double (rtx *operands, bool emit, int *count)
         case PRE_DEC:
 	  if (emit)
 	    {
-	      if (TARGET_LDRD)
+	      if (allow_strd)
 		output_asm_insn ("strd%?\t%1, [%m0, #-8]!", operands);
 	      else
 		output_asm_insn ("stmdb%?\t%m0!, %M1", operands);
@@ -18494,7 +18500,7 @@ output_move_double (rtx *operands, bool emit, int *count)
         case POST_INC:
 	  if (emit)
 	    {
-	      if (TARGET_LDRD)
+	      if (allow_strd)
 		output_asm_insn ("strd%?\t%1, [%m0], #8", operands);
 	      else
 		output_asm_insn ("stm%?\t%m0!, %M1", operands);
@@ -18502,7 +18508,7 @@ output_move_double (rtx *operands, bool emit, int *count)
 	  break;
 
         case POST_DEC:
-	  gcc_assert (TARGET_LDRD);
+	  gcc_assert (allow_strd);
 	  if (emit)
 	    output_asm_insn ("strd%?\t%1, [%m0], #-8", operands);
 	  break;
@@ -18513,8 +18519,8 @@ output_move_double (rtx *operands, bool emit, int *count)
 	  otherops[1] = XEXP (XEXP (XEXP (operands[0], 0), 1), 0);
 	  otherops[2] = XEXP (XEXP (XEXP (operands[0], 0), 1), 1);
 
-	  /* IWMMXT allows offsets larger than ldrd can handle,
-	     fix these up with a pair of ldr.  */
+	  /* IWMMXT allows offsets larger than strd can handle,
+	     fix these up with a pair of str.  */
 	  if (!TARGET_THUMB2
 	      && CONST_INT_P (otherops[2])
 	      && (INTVAL(otherops[2]) <= -256
@@ -18579,7 +18585,7 @@ output_move_double (rtx *operands, bool emit, int *count)
 		  return "";
 		}
 	    }
-	  if (TARGET_LDRD
+	  if (allow_strd
 	      && (REG_P (otherops[2])
 		  || TARGET_THUMB2
 		  || (CONST_INT_P (otherops[2])

gcc/testsuite/ChangeLog

+2018-06-29  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
+
+	* gcc.target/arm/arm-soft-strd-even.c: New test.
+
 2018-06-29  Tom de Vries  <tdevries@suse.de>
 
 	* gcc.dg/guality/pr45882.c (foo): Add line number var for breakpoint

gcc/testsuite/gcc.target/arm/arm-soft-strd-even.c

+/* { dg-do assemble } */
+/* { dg-require-effective-target arm_arm_ok } */
+/* { dg-options "-O2 -marm -mfloat-abi=soft" } */
+
+/* Check that we don't try to emit STRD in ARM state with
+   odd starting register.  */
+
+struct S {
+  double M0;
+} __attribute((aligned)) __attribute((packed));
+
+void bar(void *);
+
+void foo(int x, struct S y) {
+  asm("" : : : "r1", "r8", "r7", "r4");
+  y.M0 ?: bar(0);
+  bar(__builtin_alloca(8));
+}