function.c (assign_parm_setup_block): Explicitly convert BLKmode parameters from…

function.c (assign_parm_setup_block): Explicitly convert BLKmode parameters from word_mode to the subword type if...

gcc/
	* function.c (assign_parm_setup_block): Explicitly convert BLKmode
	parameters from word_mode to the subword type if such a truncation
	is not a no-op.

From-SVN: r128696

gcc/ChangeLog

+2007-09-23  Richard Sandiford  <rsandifo@nildram.co.uk>
+
+	* function.c (assign_parm_setup_block): Explicitly convert BLKmode
+	parameters from word_mode to the subword type if such a truncation
+	is not a no-op.
+
 2007-09-23  Jakub Jelinek  <jakub@redhat.com>
 
 	* configure.ac (MAKEINFO): Handle makeinfo version 4.10 and above.

gcc/function.c

@@ -2591,7 +2591,21 @@ assign_parm_setup_block (struct assign_parm_data_all *all,
 #endif
 	      )
 	    {
-	      rtx reg = gen_rtx_REG (mode, REGNO (entry_parm));
+	      rtx reg;
+
+	      /* We are really truncating a word_mode value containing
+		 SIZE bytes into a value of mode MODE.  If such an
+		 operation requires no actual instructions, we can refer
+		 to the value directly in mode MODE, otherwise we must
+		 start with the register in word_mode and explicitly
+		 convert it.  */
+	      if (TRULY_NOOP_TRUNCATION (size * BITS_PER_UNIT, BITS_PER_WORD))
+		reg = gen_rtx_REG (mode, REGNO (entry_parm));
+	      else
+		{
+		  reg = gen_rtx_REG (word_mode, REGNO (entry_parm));
+		  reg = convert_to_mode (mode, copy_to_reg (reg), 1);
+		}
 	      emit_move_insn (change_address (mem, mode, 0), reg);
 	    }