[gcc r11-8180] [PR100066] Check paradoxical subreg when splitting hard reg live range

[Vladimir Makarov <vmakarov@gcc.gnu.org>]

https://gcc.gnu.org/g:f99f64f69db49ce6343d79a39eab28dcc6b91865

commit r11-8180-gf99f64f69db49ce6343d79a39eab28dcc6b91865
Author: Vladimir N. Makarov <vmakarov@redhat.com>
Date:   Wed Apr 14 13:21:40 2021 -0400

    [PR100066] Check paradoxical subreg when splitting hard reg live range
    
    When splitting live range of a hard reg, LRA actually split multi-register
    containing the hard reg.  So we need to check the biggest used mode of the hard reg on
    paradoxical subregister when the natural and the biggest
    mode are ordered.
    
    gcc/ChangeLog:
    
            PR rtl-optimization/100066
            * lra-constraints.c (split_reg): Check paradoxical_subreg_p for
            ordered modes when choosing splitting mode for hard reg.
    
    gcc/testsuite/ChangeLog:
    
            PR rtl-optimization/100066
            * gcc.target/i386/pr100066.c: New.

Diff:
---
 gcc/lra-constraints.c                    | 12 ++++++++----
 gcc/testsuite/gcc.target/i386/pr100066.c | 13 +++++++++++++
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/gcc/lra-constraints.c b/gcc/lra-constraints.c
index 62bcfc31772..9425f2d7e73 100644
--- a/gcc/lra-constraints.c
+++ b/gcc/lra-constraints.c
@@ -5797,10 +5797,14 @@ split_reg (bool before_p, int original_regno, rtx_insn *insn,
       mode = lra_reg_info[hard_regno].biggest_mode;
       machine_mode reg_rtx_mode = GET_MODE (regno_reg_rtx[hard_regno]);
       /* A reg can have a biggest_mode of VOIDmode if it was only ever seen as
-	 part of a multi-word register.  In that case, just use the reg_rtx.
-	 Otherwise, limit the size to that of the biggest access in the
-	 function.  */
-      if (mode == VOIDmode)
+	 part of a multi-word register.  In that case, just use the reg_rtx
+	 mode.  Do the same also if the biggest mode was larger than a register
+	 or we can not compare the modes.  Otherwise, limit the size to that of
+	 the biggest access in the function.  */
+      if (mode == VOIDmode
+	  || !ordered_p (GET_MODE_PRECISION (mode),
+			 GET_MODE_PRECISION (reg_rtx_mode))
+	  || paradoxical_subreg_p (mode, reg_rtx_mode))
 	{
 	  original_reg = regno_reg_rtx[hard_regno];
 	  mode = reg_rtx_mode;
diff --git a/gcc/testsuite/gcc.target/i386/pr100066.c b/gcc/testsuite/gcc.target/i386/pr100066.c
new file mode 100644
index 00000000000..a795864e172
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr100066.c
@@ -0,0 +1,13 @@
+/* { dg-do compile { target { int128 } } } */
+/* { dg-options "-O1 -w" } */
+int pm;
+
+void
+w3 (int, int, int);
+
+void
+e6 (__int128 rt, long int mo)
+{
+  mo += rt / 0;
+  w3 (pm / mo, pm, 0);
+}