dwarf2asm: Use constexpr for eh_data_format_name initialization for C++14

Similarly to the previous patch, dwarf2asm.cc had
HAVE_DESIGNATED_INITIALIZERS support, and as fallback a huge switch.
The switch from what I can see is expanded as a jump table with 256
label pointers and code at those labels then loads addresses of
string literals.
The following patch instead uses a table with 256 const char * pointers,
NULL for ICE, non-NULL for returning something, similarly to the
HAVE_DESIGNATED_INITIALIZERS case.

2024-09-19  Jakub Jelinek  <jakub@redhat.com>

	* dwarf2asm.cc (eh_data_format_name): Use constexpr initialization
	of format_names table for C++14 instead of a large switch.

diff --git a/gcc/dwarf2asm.cc b/gcc/dwarf2asm.cc
index 6c835bafbc461605e88096f7b8cbb0d8f86169c2..72e831af99edef7a627ab311fa9f0cd0b78600a1 100644 (file)
--- a/gcc/dwarf2asm.cc
+++ b/gcc/dwarf2asm.cc
@@ -488,14 +488,22 @@ eh_data_format_name (int format)
 {
 #if HAVE_DESIGNATED_INITIALIZERS
 #define S(p, v)                [p] = v,
+#elif __cpp_constexpr >= 201304L
+#define S(p, v)                names[p] = v;
 #else
 #define S(p, v)                case p: return v;
 #endif
 
 #if HAVE_DESIGNATED_INITIALIZERS
   __extension__ static const char * const format_names[256] = {
+#elif __cpp_constexpr >= 201304L
+  static constexpr struct format_names_s {
+    const char *names[256];
+    constexpr format_names_s () : names {}
+    {
 #else
-  switch (format) {
+  switch (format)
+    {
 #endif
 
   S(DW_EH_PE_absptr, "absolute")
@@ -635,8 +643,15 @@ eh_data_format_name (int format)
   gcc_assert (format >= 0 && format < 0x100 && format_names[format]);
 
   return format_names[format];
+#elif __cpp_constexpr >= 201304L
+    }
+  } format_names;
+
+  gcc_assert (format >= 0 && format < 0x100 && format_names.names[format]);
+
+  return format_names.names[format];
 #else
-  }
+    }
   gcc_unreachable ();
 #endif
 }