| Message ID | 009d01d99993$0a433840$1ec9a8c0$@nextmovesoftware.com |
|---|---|
| State | New |
| Headers | show |
| Series | [Committed] Bug fix to new wi::bitreverse_large function. | expand |
diff --git a/gcc/wide-int.cc b/gcc/wide-int.cc index 24bdce2..ab92ee6 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; } }
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. Thanks, Roger --