Fixed problem with BTF defining smaller enums.

This patch fixes a BTF, which would become invalid when having
smaller then 4 byte definitions of enums.
For example, when using the __attribute__((mode(byte))) in the enum
definition.

Two problems were identified:
 - it would incorrectly create an entry for enum64 when the size of the
   enum was different then 4.
 - it would allocate less then 4 bytes for the value entry in BTF, in
   case the type was smaller.

BTF generated was validated against clang.

gcc/ChangeLog:
	* btfout.cc (btf_calc_num_vbytes): Fixed logic for enum64.
	(btf_asm_enum_const): Corrected logic for enum64 and smaller
	than 4 bytes values.

gcc/testsuite/ChangeLog:
	* gcc.dg/debug/btf/btf-enum-small.c: Added test.

1 files changed, 28 insertions, 0 deletions

diff --git a/gcc/testsuite/gcc.dg/debug/btf/btf-enum-small.c b/gcc/testsuite/gcc.dg/debug/btf/btf-enum-small.c
new file mode 100644
index 0000000..eb8a1bd
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/debug/btf/btf-enum-small.c
@@ -0,0 +1,28 @@
+/* Test BTF generation for small enums.  */
+
+/* { dg-do compile } */
+/* { dg-options "-O2 -gbtf -dA" } */
+
+/* { dg-final { scan-assembler-not "bte_value_lo32" } } */
+/* { dg-final { scan-assembler-not "bte_value_hi32" } } */
+/* { dg-final { scan-assembler-times "\[\t \]0x6000002\[\t \]+\[^\n\]*btt_info" 1 } } */
+/* { dg-final { scan-assembler-times " ENUM_CONST 'eSMALL' idx=0" 1 } } */
+/* { dg-final { scan-assembler-times " ENUM_CONST 'eSMALLY' idx=1" 1 } } */
+/* { dg-final { scan-assembler-times "ascii \"eSMALL.0\"\[\t \]+\[^\n\]*btf_string" 1 } } */
+/* { dg-final { scan-assembler-times "ascii \"eSMALLY.0\"\[\t \]+\[^\n\]*btf_string" 1 } } */
+/* { dg-final { scan-assembler-times "bte_value" 2 } } */
+
+enum smalled_enum
+{
+  eSMALL,
+  eSMALLY,
+} __attribute__((mode(byte)));
+
+struct root_struct {
+  enum smalled_enum esmall;
+};
+
+enum smalled_enum
+foo(struct root_struct *root) {
+  return root->esmall;
+}