[backport from gcc-4.8/trunk r189681 <mikpe@it.uu.se>]

gcc/

2012-07-19  Jakub Jelinek  <jakub@redhat.com>

	PR rtl-optimization/53942
	* function.c (assign_parm_setup_reg): Avoid zero/sign extension
	directly from likely spilled non-fixed hard registers, move them
	to pseudo first.

gcc/testsuite/

2012-07-19  Jakub Jelinek  <jakub@redhat.com>

	PR rtl-optimization/53942
	* gcc.dg/pr53942.c: New test.

--- gcc-4.6.3/gcc/function.c.~1~	2012-02-09 11:10:36.000000000 +0100
+++ gcc-4.6.3/gcc/function.c	2012-08-11 15:51:47.000000000 +0200
@@ -3017,11 +3017,26 @@ assign_parm_setup_reg (struct assign_par
 	  && insn_data[icode].operand[1].predicate (op1, data->passed_mode))
 	{
 	  enum rtx_code code = unsignedp ? ZERO_EXTEND : SIGN_EXTEND;
-	  rtx insn, insns;
+	  rtx insn, insns, t = op1;
 	  HARD_REG_SET hardregs;
 
 	  start_sequence ();
-	  insn = gen_extend_insn (op0, op1, promoted_nominal_mode,
+	  /* If op1 is a hard register that is likely spilled, first
+	     force it into a pseudo, otherwise combiner might extend
+	     its lifetime too much.  */
+	  if (GET_CODE (t) == SUBREG)
+	    t = SUBREG_REG (t);
+	  if (REG_P (t)
+	      && HARD_REGISTER_P (t)
+	      && ! TEST_HARD_REG_BIT (fixed_reg_set, REGNO (t))
+	      && targetm.class_likely_spilled_p (REGNO_REG_CLASS (REGNO (t))))
+	    {
+	      t = gen_reg_rtx (GET_MODE (op1));
+	      emit_move_insn (t, op1);
+	    }
+	  else
+	    t = op1;
+	  insn = gen_extend_insn (op0, t, promoted_nominal_mode,
 				  data->passed_mode, unsignedp);
 	  emit_insn (insn);
 	  insns = get_insns ();
--- gcc-4.6.3/gcc/testsuite/gcc.dg/pr53942.c.~1~	1970-01-01 01:00:00.000000000 +0100
+++ gcc-4.6.3/gcc/testsuite/gcc.dg/pr53942.c	2012-08-11 15:51:47.000000000 +0200
@@ -0,0 +1,34 @@
+/* PR rtl-optimization/53942 */
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+/* { dg-options "-O2 -mtune=pentium2" { target { { i?86-*-* x86_64-*-* } && ilp32 } } } */
+
+struct S
+{
+  unsigned short w[3];
+  unsigned int x, y;
+};
+
+struct S *baz (void);
+
+__attribute__ ((noinline))
+static unsigned char
+foo (struct S *x, unsigned char y)
+{
+  unsigned char c = 0;
+  unsigned char v = x->w[0];
+  c |= v;
+  v = ((x->w[1]) & (1 << y)) ? 1 : 0;
+  c |= v << 1;
+  v = ((x->w[2]) & 0xff) & (1 << y);
+  c |= v << 2;
+  return c;
+}
+
+void
+bar (void)
+{
+  struct S *s = baz ();
+  s->x = foo (s, 6);
+  s->y = foo (s, 7);
+}