[PATCH] arm: Fix multiple inheritance thunks for thumb-1 with -mpure-code

[Christophe Lyon]

When mi_delta is > 255 and -mpure-code is used, we cannot load delta
from code memory (like we do without -mpure-code).

This patch builds the value of mi_delta into r3 with a series of
movs/adds/lsls.

We also do some cleanup by not emitting the function address and delta
via .word directives at the end of the thunk since we don't use them
with -mpure-code.

No need for new testcases, this bug was already identified by
eg. pr46287-3.C

2020-09-29  Christophe Lyon  <christophe.lyon@linaro.org>

	gcc/
	* config/arm/arm.c (arm_thumb1_mi_thunk): Build mi_delta in r3 and
	do not emit function address and delta when -mpure-code is used.

k#   (use "git pull" to merge the remote branch into yours)
---
 gcc/config/arm/arm.c | 91 +++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 66 insertions(+), 25 deletions(-)

diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
index ceeb91f..62abeb5 100644
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -28342,9 +28342,43 @@ arm_thumb1_mi_thunk (FILE *file, tree, HOST_WIDE_INT delta,
     {
       if (mi_delta > 255)
 	{
-	  fputs ("\tldr\tr3, ", file);
-	  assemble_name (file, label);
-	  fputs ("+4\n", file);
+	  /* With -mpure-code, we cannot load delta from the constant
+	     pool: we build it explicitly.  */
+	  if (target_pure_code)
+	    {
+	      bool mov_done_p = false;
+	      int i;
+
+	      /* Emit upper 3 bytes if needed.  */
+	      for (i = 0; i < 3; i++)
+		{
+		  int byte = (mi_delta >> (8 * (3 - i))) & 0xff;
+
+		  if (byte)
+		    {
+		      if (mov_done_p)
+			asm_fprintf (file, "\tadds\tr3, #%d\n", byte);
+		      else
+			asm_fprintf (file, "\tmovs\tr3, #%d\n", byte);
+		      mov_done_p = true;
+		    }
+
+		  if (mov_done_p)
+		    asm_fprintf (file, "\tlsls\tr3, #8\n");
+		}
+
+	      /* Emit lower byte if needed.  */
+	      if (!mov_done_p)
+		asm_fprintf (file, "\tmovs\tr3, #%d\n", mi_delta & 0xff);
+	      else if (mi_delta & 0xff)
+		asm_fprintf (file, "\tadds\tr3, #%d\n", mi_delta & 0xff);
+	    }
+	  else
+	    {
+	      fputs ("\tldr\tr3, ", file);
+	      assemble_name (file, label);
+	      fputs ("+4\n", file);
+	    }
 	  asm_fprintf (file, "\t%ss\t%r, %r, r3\n",
 		       mi_op, this_regno, this_regno);
 	}
@@ -28380,30 +28414,37 @@ arm_thumb1_mi_thunk (FILE *file, tree, HOST_WIDE_INT delta,
 	fputs ("\tpop\t{r3}\n", file);
 
       fprintf (file, "\tbx\tr12\n");
-      ASM_OUTPUT_ALIGN (file, 2);
-      assemble_name (file, label);
-      fputs (":\n", file);
-      if (flag_pic)
+
+      /* With -mpure-code, we don't need to emit literals for the
+	 function address and delta since we emitted code to build
+	 them.  */
+      if (!target_pure_code)
 	{
-	  /* Output ".word .LTHUNKn-[3,7]-.LTHUNKPCn".  */
-	  rtx tem = XEXP (DECL_RTL (function), 0);
-	  /* For TARGET_THUMB1_ONLY the thunk is in Thumb mode, so the PC
-	     pipeline offset is four rather than eight.  Adjust the offset
-	     accordingly.  */
-	  tem = plus_constant (GET_MODE (tem), tem,
-			       TARGET_THUMB1_ONLY ? -3 : -7);
-	  tem = gen_rtx_MINUS (GET_MODE (tem),
-			       tem,
-			       gen_rtx_SYMBOL_REF (Pmode,
-						   ggc_strdup (labelpc)));
-	  assemble_integer (tem, 4, BITS_PER_WORD, 1);
-	}
-      else
-	/* Output ".word .LTHUNKn".  */
-	assemble_integer (XEXP (DECL_RTL (function), 0), 4, BITS_PER_WORD, 1);
+	  ASM_OUTPUT_ALIGN (file, 2);
+	  assemble_name (file, label);
+	  fputs (":\n", file);
+	  if (flag_pic)
+	    {
+	      /* Output ".word .LTHUNKn-[3,7]-.LTHUNKPCn".  */
+	      rtx tem = XEXP (DECL_RTL (function), 0);
+	      /* For TARGET_THUMB1_ONLY the thunk is in Thumb mode, so the PC
+		 pipeline offset is four rather than eight.  Adjust the offset
+		 accordingly.  */
+	      tem = plus_constant (GET_MODE (tem), tem,
+				   TARGET_THUMB1_ONLY ? -3 : -7);
+	      tem = gen_rtx_MINUS (GET_MODE (tem),
+				   tem,
+				   gen_rtx_SYMBOL_REF (Pmode,
+						       ggc_strdup (labelpc)));
+	      assemble_integer (tem, 4, BITS_PER_WORD, 1);
+	    }
+	  else
+	    /* Output ".word .LTHUNKn".  */
+	    assemble_integer (XEXP (DECL_RTL (function), 0), 4, BITS_PER_WORD, 1);
 
-      if (TARGET_THUMB1_ONLY && mi_delta > 255)
-	assemble_integer (GEN_INT(mi_delta), 4, BITS_PER_WORD, 1);
+	  if (TARGET_THUMB1_ONLY && mi_delta > 255)
+	    assemble_integer (GEN_INT(mi_delta), 4, BITS_PER_WORD, 1);
+	}
     }
   else
     {
-- 
2.7.4