LTO: Get rid of 'lto_mode_identity_table' (was: Machine Mode ICE in RISC-V when LTO)

[Thomas Schwinge <thomas@codesourcery.com>]

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Hi!

On 2023-09-15T15:33:59+0200, Robin Dapp <rdapp.gcc@gmail.com> wrote:
> is there anything we can do to assist from the riscv side in order to help
> with this?  I haven't really been involved with it but was wondering
> what's missing.  If I understand correctly Thomas has a major cleanup
> operation in plan

Not really major, but indeed non-trivial -- but WIP already.  ;-)

> but might not get to it soon.

Right.

> The fix he proposed
> helps for the riscv case, however, even without the rework?

Right, and no harm done for my work.

> If so, I'd kindly ping Jakub to check if the fix is reasonable.

I'll push the attached "LTO: Get rid of 'lto_mode_identity_table'"
mid-week, unless any objections raised.


Grüße
 Thomas


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From f88a923d7e3e26c29630f1b20624fa54032f8e96 Mon Sep 17 00:00:00 2001
From: Thomas Schwinge <thomas@codesourcery.com>
Date: Thu, 10 Aug 2023 15:23:37 +0200
Subject: [PATCH] LTO: Get rid of 'lto_mode_identity_table'

This, in particular, resolves LTO ICEs with big 'machine_mode's, as for RISC-V.
('mode_table' in 'lto_file_decl_data' still is 'unsigned char'; changing that
is still to be done (for use in offloading compilation), but is not trivial.)
For now, get rid of 'lto_mode_identity_table' to resolve the RISC-V LTO ICEs;
we don't need an actual table for a 1-to-1 mapping.

	gcc/lto/
	* lto-common.cc (lto_mode_identity_table): Remove.
	(lto_file_finalize) [!ACCEL_COMPILER]: 'NULL'-intialize
	'file_data->mode_table'.
	(lto_fe_init): Don't initialize 'lto_mode_identity_table'.
	* lto-common.h (lto_mode_identity_table): Remove.
	gcc/
	* tree-streamer.h (bp_unpack_machine_mode): If
	'ib->file_data->mode_table' not available, apply 1-to-1 mapping.

Co-authored-by: Pan Li <pan2.li@intel.com>
---
 gcc/lto/lto-common.cc | 11 +----------
 gcc/lto/lto-common.h  |  1 -
 gcc/tree-streamer.h   |  5 ++++-
 3 files changed, 5 insertions(+), 12 deletions(-)

diff --git a/gcc/lto/lto-common.cc b/gcc/lto/lto-common.cc
index 703e665b698..ad6e7fde5ce 100644
--- a/gcc/lto/lto-common.cc
+++ b/gcc/lto/lto-common.cc
@@ -64,8 +64,6 @@ static bool type_streaming_finished = false;
 
 GTY(()) tree first_personality_decl;
 
-GTY(()) const unsigned char *lto_mode_identity_table;
-
 /* Returns a hash code for P.  */
 
 static hashval_t
@@ -2277,7 +2275,7 @@ lto_file_finalize (struct lto_file_decl_data *file_data, lto_file *file,
 #ifdef ACCEL_COMPILER
   lto_input_mode_table (file_data);
 #else
-  file_data->mode_table = lto_mode_identity_table;
+  file_data->mode_table = NULL;
   file_data->mode_bits = ceil_log2 (MAX_MACHINE_MODE);
 #endif
 
@@ -3118,13 +3116,6 @@ lto_fe_init (void)
   memset (&lto_stats, 0, sizeof (lto_stats));
   bitmap_obstack_initialize (NULL);
   gimple_register_cfg_hooks ();
-#ifndef ACCEL_COMPILER
-  unsigned char *table
-    = ggc_vec_alloc<unsigned char> (MAX_MACHINE_MODE);
-  for (int m = 0; m < MAX_MACHINE_MODE; m++)
-    table[m] = m;
-  lto_mode_identity_table = table;
-#endif
 }
 
 #include "gt-lto-lto-common.h"
diff --git a/gcc/lto/lto-common.h b/gcc/lto/lto-common.h
index 24b2445673b..b9faa72e5cb 100644
--- a/gcc/lto/lto-common.h
+++ b/gcc/lto/lto-common.h
@@ -26,7 +26,6 @@ void print_lto_report_1 (void);
 
 extern tree lto_eh_personality_decl;
 extern GTY(()) vec<tree, va_gc> *tree_with_vars;
-extern const unsigned char *lto_mode_identity_table;
 extern tree first_personality_decl;
 
 #endif
diff --git a/gcc/tree-streamer.h b/gcc/tree-streamer.h
index ff49d1ba637..886ee6ac754 100644
--- a/gcc/tree-streamer.h
+++ b/gcc/tree-streamer.h
@@ -118,7 +118,10 @@ bp_unpack_machine_mode (struct bitpack_d *bp)
   lto_input_block *ib = (class lto_input_block *) bp->stream;
   int last = 1 << ib->file_data->mode_bits;
   unsigned ix = bp_unpack_enum (bp, machine_mode, last);
-  return (machine_mode) ib->file_data->mode_table[ix];
+  if (ib->file_data->mode_table)
+    return (machine_mode) ib->file_data->mode_table[ix];
+  else
+    return (machine_mode) ix;
 }
 
 #endif  /* GCC_TREE_STREAMER_H  */
-- 
2.34.1