From ad7a365aaccecd23ea287c7faaab9c7bd50b944a Mon Sep 17 00:00:00 2001
From: Richard Biener <rguenther@suse.de>
Date: Wed, 14 Feb 2024 12:33:13 +0100
Subject: [PATCH] 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.
---
gcc/bitmap.cc | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
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);
}
--
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