[gcc r12-3457] Revert "Get rid of all float-int special cases in validate_subreg."

[hongtao Liu <liuhongt@gcc.gnu.org>]

https://gcc.gnu.org/g:57b7c432cce893e1ba60d9b94a9606df6b419379

commit r12-3457-g57b7c432cce893e1ba60d9b94a9606df6b419379
Author: liuhongt <hongtao.liu@intel.com>
Date:   Fri Sep 10 20:02:25 2021 +0800

    Revert "Get rid of all float-int special cases in validate_subreg."
    
    This reverts commit d2874d905647a1d146dafa60199d440e837adc4d.
    
    PR target/102254
    PR target/102154
    PR target/102211

Diff:
---
 gcc/emit-rtl.c | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/gcc/emit-rtl.c b/gcc/emit-rtl.c
index 77ea8948ee8..ff3b4449b37 100644
--- a/gcc/emit-rtl.c
+++ b/gcc/emit-rtl.c
@@ -922,6 +922,46 @@ validate_subreg (machine_mode omode, machine_mode imode,
 
   poly_uint64 regsize = REGMODE_NATURAL_SIZE (imode);
 
+  /* ??? This should not be here.  Temporarily continue to allow word_mode
+     subregs of anything.  The most common offender is (subreg:SI (reg:DF)).
+     Generally, backends are doing something sketchy but it'll take time to
+     fix them all.  */
+  if (omode == word_mode)
+    ;
+  /* ??? Similarly, e.g. with (subreg:DF (reg:TI)).  Though store_bit_field
+     is the culprit here, and not the backends.  */
+  else if (known_ge (osize, regsize) && known_ge (isize, osize))
+    ;
+  /* Allow component subregs of complex and vector.  Though given the below
+     extraction rules, it's not always clear what that means.  */
+  else if ((COMPLEX_MODE_P (imode) || VECTOR_MODE_P (imode))
+	   && GET_MODE_INNER (imode) == omode)
+    ;
+  /* ??? x86 sse code makes heavy use of *paradoxical* vector subregs,
+     i.e. (subreg:V4SF (reg:SF) 0) or (subreg:V4SF (reg:V2SF) 0).  This
+     surely isn't the cleanest way to represent this.  It's questionable
+     if this ought to be represented at all -- why can't this all be hidden
+     in post-reload splitters that make arbitrarily mode changes to the
+     registers themselves.  */
+  else if (VECTOR_MODE_P (omode)
+	   && GET_MODE_INNER (omode) == GET_MODE_INNER (imode))
+    ;
+  /* Subregs involving floating point modes are not allowed to
+     change size.  Therefore (subreg:DI (reg:DF) 0) is fine, but
+     (subreg:SI (reg:DF) 0) isn't.  */
+  else if (FLOAT_MODE_P (imode) || FLOAT_MODE_P (omode))
+    {
+      if (! (known_eq (isize, osize)
+	     /* LRA can use subreg to store a floating point value in
+		an integer mode.  Although the floating point and the
+		integer modes need the same number of hard registers,
+		the size of floating point mode can be less than the
+		integer mode.  LRA also uses subregs for a register
+		should be used in different mode in on insn.  */
+	     || lra_in_progress))
+	return false;
+    }
+
   /* Paradoxical subregs must have offset zero.  */
   if (maybe_gt (osize, isize))
     return known_eq (offset, 0U);