[SPARC] Fix miscompilation of Ada runtime in 64-bit mode

[Eric Botcazou]

Returning a REGMODE_NATURAL_SIZE of 4 for DFmode in 64-bit mode is asking for 
trouble because sub-word SUBREGs are always treated differently than the 
others, in particular by the register allocator.

Bootstrapped/regtested on SPARC64/Linux and SPARC/Solaris, applied on the 
mainline.


2021-03-10  Eric Botcazou  <ebotca...@adacore.com>

        * config/sparc/sparc.c (sparc_regmode_natural_size): Return 4 for
        float and vector integer modes only if the mode is not larger.

-- 
Eric Botcazou
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.