https://bugs.llvm.org/show_bug.cgi?id=41178
Bug ID: 41178
Summary: clang strict-aliasing optimizations vs unreachable
code
Product: libraries
Version: 7.0
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: Scalar Optimizations
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Created attachment 21640
--> https://bugs.llvm.org/attachment.cgi?id=21640&action=edit
test with unreachable code
Lets consider example r.c from attachment
$ clang-7.0 -O0 r.c -o r0.out
$ clang-7.0 -O1 r.c -fno-strict-aliasing -o r1.nsa.out
$ clang-7.0 -O1 r.c -o r1.sa.out
$ ./r0.out
this should be zero: 0
$ ./r1.nsa.out
this should be zero: 0
$ ./r1.sa.out
this should be zero: -1
static inline void __attribute__((always_inline)) longLongAssign( int cond,
char *ptr)
{
if ( cond )
{
*((long long *)ptr) = 0;
}
}
I suppose test doesn't violate strict-aliasing rule, because
1) argument "ptr" has type "char *"
2) condition "cond" is always zero
Why I got different results?
P.S. I am new therefore apologize for my mistakes.
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