[gcc r14-1626] [Committed] Bug fix to new wi::bitreverse_large function.

[gcc r14-1626] [Committed] Bug fix to new wi::bitreverse_large function.

[Roger Sayle]

https://gcc.gnu.org/g:e73a307f5027aeb124fa824621ad980aa983931b

commit r14-1626-ge73a307f5027aeb124fa824621ad980aa983931b
Author: Roger Sayle <roger@nextmovesoftware.com>
Date:   Wed Jun 7 23:40:56 2023 +0100

    [Committed] Bug fix to new wi::bitreverse_large function.
    
    Richard Sandiford was, of course, right to be warry of new code without
    much test coverage.  Converting the nvptx backend to use the BITREVERSE
    rtx infrastructure, has resulted in far more exhaustive testing and
    revealed a subtle bug in the new wi::bitreverse implementation.  The
    code needs to use HOST_WIDE_INT_1U (instead of 1) to avoid unintended
    sign extension.
    
    This patch has been tested on nvptx-none hosted on x86_64-pc-linux-gnu
    (with a minor tweak to use BITREVERSE), where it fixes regressions of
    the 32-bit test vectors in gcc.target/nvptx/brev-2.c and the 64-bit
    test vectors in gcc.target/nvptx/brevll-2.c.  Committed as obvious.
    
    2023-06-07  Roger Sayle  <roger@nextmovesoftware.com>
    
    gcc/ChangeLog
            * wide-int.cc (wi::bitreverse_large): Use HOST_WIDE_INT_1U to
            avoid sign extension/undefined behaviour when setting each bit.

Diff:
---
 gcc/wide-int.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gcc/wide-int.cc b/gcc/wide-int.cc
index 24bdce2a656..c6a9e2d49b2 100644
--- a/gcc/wide-int.cc
+++ b/gcc/wide-int.cc
@@ -786,7 +786,7 @@ wi::bitreverse_large (HOST_WIDE_INT *val, const HOST_WIDE_INT *xval,
 	  unsigned int d = (precision - 1) - s;
 	  block = d / HOST_BITS_PER_WIDE_INT;
 	  offset = d & (HOST_BITS_PER_WIDE_INT - 1);
-          val[block] |= 1 << offset;
+	  val[block] |= HOST_WIDE_INT_1U << offset;
 	}
     }