http://llvm.org/bugs/show_bug.cgi?id=7373
Summary: INT_MIN % -1 is not undefined
Product: new-bugs
Version: unspecified
Platform: PC
OS/Version: Linux
Status: NEW
Severity: normal
Priority: P
Component: new bugs
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
clang says that INT_MIN % -1 is undefined (see below) but I don't think the
standard justifies this. In N1124 at 6.5.5.5 we have
"The result of the / operator is the quotient from the division of the first
operand by the second; the result of the % operator is the remainder. In both
operations, if the value of the second operand is zero, the behavior is
undefined."
This seems pretty clear: the result should be 0.
My guess is that whoever made this undefined was reading from 6.5.5.6:
"When integers are divided, the result of the / operator is the algebraic
quotient with any fractional part discarded. If the quotient a/b is
representable, the expression (a/b)*b + a%b shall equal a."
But I don't buy it. We have an equality that must hold when a/b is
representable, but it never says that a%b is undefined when a/b is not
representable.
reg...@john-home:~$ cat test.c
#include <limits.h>
int foo (void)
{
return INT_MIN % -1;
}
reg...@john-home:~$ clang test.c -S -emit-llvm -O -o -
; ModuleID = 'test.c'
target datalayout =
"e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:32:32-n8:16:32"
target triple = "i386-pc-linux-gnu"
define i32 @foo() nounwind readnone {
entry:
ret i32 undef
}
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