[gcc r11-7593] Fix miscompilation of Ada runtime on 64-bit SPARC

[Eric Botcazou]

https://gcc.gnu.org/g:da7343a6f48c6813a29640fec744b0a236b6540f

commit r11-7593-gda7343a6f48c6813a29640fec744b0a236b6540f
Author: Eric Botcazou <ebotcazou@adacore.com>
Date:   Wed Mar 10 12:02:14 2021 +0100

    Fix miscompilation of Ada runtime on 64-bit SPARC
    
    Returning a REGMODE_NATURAL_SIZE of 4 for DFmode in 64-bit mode is
    just asking for trouble because sub-word SUBREGs are always treated
    differently than the others, in particular by the register allocator.
    
    gcc/
            * config/sparc/sparc.c (sparc_regmode_natural_size): Return 4 for
            float and vector integer modes only if the mode is not larger.

Diff:
---
 gcc/config/sparc/sparc.c | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/gcc/config/sparc/sparc.c b/gcc/config/sparc/sparc.c
index f3557936114..f1504172022 100644
--- a/gcc/config/sparc/sparc.c
+++ b/gcc/config/sparc/sparc.c
@@ -13585,23 +13585,18 @@ sparc_expand_vcond (machine_mode mode, rtx *operands, int ccode, int fcode)
   emit_insn (gen_rtx_SET (operands[0], bshuf));
 }
 
-/* On sparc, any mode which naturally allocates into the float
+/* On the SPARC, any mode which naturally allocates into the single float
    registers should return 4 here.  */
 
 unsigned int
 sparc_regmode_natural_size (machine_mode mode)
 {
-  int size = UNITS_PER_WORD;
+  const enum mode_class cl = GET_MODE_CLASS (mode);
 
-  if (TARGET_ARCH64)
-    {
-      enum mode_class mclass = GET_MODE_CLASS (mode);
-
-      if (mclass == MODE_FLOAT || mclass == MODE_VECTOR_INT)
-	size = 4;
-    }
+  if ((cl == MODE_FLOAT || cl == MODE_VECTOR_INT) && GET_MODE_SIZE (mode) <= 4)
+    return 4;
 
-  return size;
+  return UNITS_PER_WORD;
 }
 
 /* Implement TARGET_HARD_REGNO_NREGS.