Simplify & expand c_readstr

c_readstr only operated on integer modes.  It worked by reading
the source string into an array of HOST_WIDE_INTs, converting
that array into a wide_int, and from there to an rtx.

It's simpler to do this by building a target memory image and
using native_decode_rtx to convert that memory image into an rtx.
It avoids all the endianness shenanigans because both the string and
native_decode_rtx follow target memory order.  It also means that the
function can handle all fixed-size modes, which simplifies callers
and allows vector modes to be used more widely.

gcc/
	* builtins.h (c_readstr): Take a fixed_size_mode rather than a
	scalar_int_mode.
	* builtins.cc (c_readstr): Likewise.  Build a local array of
	bytes and use native_decode_rtx to get the rtx image.
	(builtin_memcpy_read_str): Simplify accordingly.
	(builtin_strncpy_read_str): Likewise.
	(builtin_memset_read_str): Likewise.
	(builtin_memset_gen_str): Likewise.
	* expr.cc (string_cst_read_str): Likewise.

1 files changed, 2 insertions, 5 deletions

diff --git a/gcc/expr.cc b/gcc/expr.cc
index 308ddc0..2c9930e 100644
--- a/gcc/expr.cc
+++ b/gcc/expr.cc
@@ -6083,13 +6083,10 @@ string_cst_read_str (void *data, void *, HOST_WIDE_INT offset,
       size_t l = TREE_STRING_LENGTH (str) - offset;
       memcpy (p, TREE_STRING_POINTER (str) + offset, l);
       memset (p + l, '\0', GET_MODE_SIZE (mode) - l);
-      return c_readstr (p, as_a <scalar_int_mode> (mode), false);
+      return c_readstr (p, mode, false);
     }
 
-  /* The by-pieces infrastructure does not try to pick a vector mode
-     for storing STRING_CST.  */
-  return c_readstr (TREE_STRING_POINTER (str) + offset,
-		    as_a <scalar_int_mode> (mode), false);
+  return c_readstr (TREE_STRING_POINTER (str) + offset, mode, false);
 }
 
 /* Generate code for computing expression EXP,