[LLVMbugs] [Bug 21130] gvn badly replaces a call to fptosi

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Thu Oct 2 10:51:35 PDT 2014


Sanjay Patel <spatel+llvm at rotateright.com> changed:

           What    |Removed                     |Added
             Status|NEW                         |RESOLVED
                 CC|                            |spatel+llvm at rotateright.com
         Resolution|---                         |INVALID

--- Comment #3 from Sanjay Patel <spatel+llvm at rotateright.com> ---
Both the LLVM Language Ref and the C standard (annex F.4) say that the code is
undefined, so anything goes:

"If the value won’t fit in the integer type, the results are undefined."

C - floating to integer conversion:
"...if the integral part of the floating value exceeds the range of the integer
type, then the "invalid" floating-point exception is raised and the resulting
value is unspecified."

Try using lrint()?

Clang does issue warnings when it's obvious that there's a conversion problem:
$ cat 21130.c
char foo() { return 156.0; }

$ ./clang  21130.c -c
21130.c:3:12: warning: implicit conversion from 'double' to 'char' changes
value from 156 to 127 [-Wliteral-conversion]
    return 156.0;
    ~~~~~~ ^~~~~
1 warning generated.

...but your C test case is probably too complicated for that check.

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