[PATCH v2 2/4] genmodes: Use wider types for mode_unit_size array based on max size

[Avinash Jayakar]

Hi,

Addressed the comments in
https://gcc.gnu.org/pipermail/gcc-patches/2026-October/733494.html

Changes from v1:
- Correct commit message.
- Update the max value of the type size properly.
- Update type of mode_to_unit_size fn, which uses the updated array.

Bootstrapped and regtested on {x86_64,powerpc64le}-linux-gnu. Ok for
trunk?

Thanks,
Avinash

The mode_unit_size array that is generated from
emit_mode_unit_size_inline function currently hard codes the type of
this array to unsigned char, since for most architectures the
mode_unit_size never exceeded 255.

For rs6000 however, we add an opaque mode with 256 bytes which overflows
this type. Therefore this patch adds a macro named MODE_UNIT_SIZE_TYPE
in the generated file which is defined based on the maximum value that
the mode_unit_size array will hold.
if < 256, unsigned char
else if < 2^16, unsigned short
else, unsigned int

2026-10-12  Avinash Jayakar  <avina...@linux.ibm.com>

gcc/ChangeLog:
        * genmodes.cc (emit_mode_unit_size): Generate MODE_UNIT_SIZE_TYPE
        macro based on values in mode_unit_size.
        * machmode.h: Use the new macro.
---
 gcc/genmodes.cc | 21 ++++++++++++++++++---
 gcc/machmode.h  |  4 ++--
 2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/gcc/genmodes.cc b/gcc/genmodes.cc
index fa5f8923519..ed8bfd3ba3a 100644
--- a/gcc/genmodes.cc
+++ b/gcc/genmodes.cc
@@ -1167,16 +1167,31 @@ emit_mode_unit_size_inline (void)
   int c;
   struct mode_data *m;
 
+  unsigned int max_type_size = 0;
+  for_all_modes (c, m)
+    {
+      unsigned int type_size = (c != MODE_PARTIAL_INT && m->component)
+                               ? m->component->bytesize : m->bytesize;
+      if (max_type_size < type_size)
+       max_type_size = type_size;
+    }
+  if (max_type_size < (1 << 8))
+    puts ("#define MODE_UNIT_SIZE_TYPE unsigned char\n");
+  else if (max_type_size < (1 << 16))
+    puts ("#define MODE_UNIT_SIZE_TYPE unsigned short\n");
+  else
+    puts ("#define MODE_UNIT_SIZE_TYPE unsigned int\n");
+
   puts ("\
 #ifdef __cplusplus\n\
 inline __attribute__((__always_inline__))\n\
 #else\n\
 extern __inline__ __attribute__((__always_inline__, __gnu_inline__))\n\
 #endif\n\
-unsigned char\n\
+MODE_UNIT_SIZE_TYPE\n\
 mode_unit_size_inline (machine_mode mode)\n\
 {\n\
-  extern CONST_MODE_UNIT_SIZE unsigned char mode_unit_size[NUM_MACHINE_MODES];\
+  extern CONST_MODE_UNIT_SIZE MODE_UNIT_SIZE_TYPE 
mode_unit_size[NUM_MACHINE_MODES];\
 \n\
   gcc_assert (mode >= 0 && mode < NUM_MACHINE_MODES);\n\
   switch (mode)\n\
@@ -1683,7 +1698,7 @@ emit_mode_unit_size (void)
   int c;
   struct mode_data *m;
 
-  print_maybe_const_decl ("%sunsigned char", "mode_unit_size",
+  print_maybe_const_decl ("%sMODE_UNIT_SIZE_TYPE", "mode_unit_size",
                          "NUM_MACHINE_MODES", adj_bytesize);
 
   for_all_modes (c, m)
diff --git a/gcc/machmode.h b/gcc/machmode.h
index bc564d6bc13..fa439714bcb 100644
--- a/gcc/machmode.h
+++ b/gcc/machmode.h
@@ -26,7 +26,7 @@ extern CONST_MODE_SIZE poly_uint16 
mode_size[NUM_MACHINE_MODES];
 extern CONST_MODE_PRECISION poly_uint16 mode_precision[NUM_MACHINE_MODES];
 extern const unsigned short mode_inner[NUM_MACHINE_MODES];
 extern CONST_MODE_NUNITS poly_uint16 mode_nunits[NUM_MACHINE_MODES];
-extern CONST_MODE_UNIT_SIZE unsigned char mode_unit_size[NUM_MACHINE_MODES];
+extern CONST_MODE_UNIT_SIZE MODE_UNIT_SIZE_TYPE 
mode_unit_size[NUM_MACHINE_MODES];
 extern const unsigned short mode_unit_precision[NUM_MACHINE_MODES];
 extern const unsigned short mode_next[NUM_MACHINE_MODES];
 extern const unsigned short mode_wider[NUM_MACHINE_MODES];
@@ -611,7 +611,7 @@ mode_to_inner (machine_mode mode)
 
 /* Return the base GET_MODE_UNIT_SIZE value for MODE.  */
 
-ALWAYS_INLINE unsigned char
+ALWAYS_INLINE MODE_UNIT_SIZE_TYPE
 mode_to_unit_size (machine_mode mode)
 {
 #if GCC_VERSION >= 4001
-- 
2.54.0