From: Richard Biener <rguenther@suse.de>
Date: Wed, 14 Feb 2024 11:33:13 +0000 (+0100)
Subject: tree-optimization/113910 - huge compile time during PTA
X-Git-Tag: basepoints/gcc-15~1159
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ad7a365aaccecd23ea287c7faaab9c7bd50b944a;p=thirdparty%2Fgcc.git

tree-optimization/113910 - huge compile time during PTA

For the testcase in PR113910 we spend a lot of time in PTA comparing
bitmaps for looking up equivalence class members.  This points to
the very weak bitmap_hash function which effectively hashes set
and a subset of not set bits.

The major problem with it is that it simply truncates the
BITMAP_WORD sized intermediate hash to hashval_t which is
unsigned int, effectively not hashing half of the bits.

This reduces the compile-time for the testcase from tens of minutes
to 42 seconds and PTA time from 99% to 46%.

	PR tree-optimization/113910
	* bitmap.cc (bitmap_hash): Mix the full element "hash" to
	the hashval_t hash.
---

diff --git a/gcc/bitmap.cc b/gcc/bitmap.cc
index 6cf326bca5a8..459e32c1ad18 100644
--- a/gcc/bitmap.cc
+++ b/gcc/bitmap.cc
@@ -2706,7 +2706,7 @@ bitmap_hash (const_bitmap head)
       for (ix = 0; ix != BITMAP_ELEMENT_WORDS; ix++)
 	hash ^= ptr->bits[ix];
     }
-  return (hashval_t)hash;
+  return iterative_hash (&hash, sizeof (hash), 0);
 }