[PATCH 6/8] Make more use of force_lowpart_subreg

[Richard Sandiford <richard.sandiford@arm.com>]

This patch makes target-independent code use force_lowpart_subreg
instead of simplify_gen_subreg and lowpart_subreg in some places.
The criteria were:

(1) The code is obviously specific to expand (where new pseudos
    can be created), or at least would be invalid to call when
    !can_create_pseudo_p () and temporaries are needed.

(2) The value is obviously an rvalue rather than an lvalue.

Doing this should reduce the likelihood of bugs like PR115464
occuring in other situations.

gcc/
	* builtins.cc (expand_builtin_issignaling): Use force_lowpart_subreg
	instead of simplify_gen_subreg and lowpart_subreg.
	* expr.cc (convert_mode_scalar, expand_expr_real_2): Likewise.
	* optabs.cc (expand_doubleword_mod): Likewise.
---
 gcc/builtins.cc |  7 ++-----
 gcc/expr.cc     | 17 +++++++++--------
 gcc/optabs.cc   |  2 +-
 3 files changed, 12 insertions(+), 14 deletions(-)

diff --git a/gcc/builtins.cc b/gcc/builtins.cc
index 5b5307c67b8..bde517b639e 100644
--- a/gcc/builtins.cc
+++ b/gcc/builtins.cc
@@ -2940,8 +2940,7 @@ expand_builtin_issignaling (tree exp, rtx target)
 	  {
 	    hi = simplify_gen_subreg (imode, temp, fmode,
 				      subreg_highpart_offset (imode, fmode));
-	    lo = simplify_gen_subreg (imode, temp, fmode,
-				      subreg_lowpart_offset (imode, fmode));
+	    lo = force_lowpart_subreg (imode, temp, fmode);
 	    if (!hi || !lo)
 	      {
 		scalar_int_mode imode2;
@@ -2951,9 +2950,7 @@ expand_builtin_issignaling (tree exp, rtx target)
 		    hi = simplify_gen_subreg (imode, temp2, imode2,
 					      subreg_highpart_offset (imode,
 								      imode2));
-		    lo = simplify_gen_subreg (imode, temp2, imode2,
-					      subreg_lowpart_offset (imode,
-								     imode2));
+		    lo = force_lowpart_subreg (imode, temp2, imode2);
 		  }
 	      }
 	    if (!hi || !lo)
diff --git a/gcc/expr.cc b/gcc/expr.cc
index 31a7346e33f..ffbac513692 100644
--- a/gcc/expr.cc
+++ b/gcc/expr.cc
@@ -423,7 +423,8 @@ convert_mode_scalar (rtx to, rtx from, int unsignedp)
 					0).exists (&toi_mode))
 		{
 		  start_sequence ();
-		  rtx fromi = lowpart_subreg (fromi_mode, from, from_mode);
+		  rtx fromi = force_lowpart_subreg (fromi_mode, from,
+						    from_mode);
 		  rtx tof = NULL_RTX;
 		  if (fromi)
 		    {
@@ -443,7 +444,7 @@ convert_mode_scalar (rtx to, rtx from, int unsignedp)
 					      NULL_RTX, 1);
 		      if (toi)
 			{
-			  tof = lowpart_subreg (to_mode, toi, toi_mode);
+			  tof = force_lowpart_subreg (to_mode, toi, toi_mode);
 			  if (tof)
 			    emit_move_insn (to, tof);
 			}
@@ -475,7 +476,7 @@ convert_mode_scalar (rtx to, rtx from, int unsignedp)
 				    0).exists (&toi_mode))
 	    {
 	      start_sequence ();
-	      rtx fromi = lowpart_subreg (fromi_mode, from, from_mode);
+	      rtx fromi = force_lowpart_subreg (fromi_mode, from, from_mode);
 	      rtx tof = NULL_RTX;
 	      do
 		{
@@ -510,11 +511,11 @@ convert_mode_scalar (rtx to, rtx from, int unsignedp)
 						  temp4, shift, NULL_RTX, 1);
 		  if (!temp5)
 		    break;
-		  rtx temp6 = lowpart_subreg (toi_mode, temp5, fromi_mode);
+		  rtx temp6 = force_lowpart_subreg (toi_mode, temp5,
+						    fromi_mode);
 		  if (!temp6)
 		    break;
-		  tof = lowpart_subreg (to_mode, force_reg (toi_mode, temp6),
-					toi_mode);
+		  tof = force_lowpart_subreg (to_mode, temp6, toi_mode);
 		  if (tof)
 		    emit_move_insn (to, tof);
 		}
@@ -9784,9 +9785,9 @@ expand_expr_real_2 (const_sepops ops, rtx target, machine_mode tmode,
 	    inner_mode = TYPE_MODE (inner_type);
 
 	  if (modifier == EXPAND_INITIALIZER)
-	    op0 = lowpart_subreg (mode, op0, inner_mode);
+	    op0 = force_lowpart_subreg (mode, op0, inner_mode);
 	  else
-	    op0=  convert_modes (mode, inner_mode, op0,
+	    op0 = convert_modes (mode, inner_mode, op0,
 				 TYPE_UNSIGNED (inner_type));
 	}
 
diff --git a/gcc/optabs.cc b/gcc/optabs.cc
index d569742beea..185c5b1a705 100644
--- a/gcc/optabs.cc
+++ b/gcc/optabs.cc
@@ -1085,7 +1085,7 @@ expand_doubleword_mod (machine_mode mode, rtx op0, rtx op1, bool unsignedp)
 					 NULL_RTX, 1, OPTAB_DIRECT);
 	      if (v == NULL_RTX)
 		return NULL_RTX;
-	      v = lowpart_subreg (word_mode, v, mode);
+	      v = force_lowpart_subreg (word_mode, v, mode);
 	      if (v == NULL_RTX)
 		return NULL_RTX;
 	      if (i != count - 1)
-- 
2.25.1