https://bugs.llvm.org/show_bug.cgi?id=44913
Bug ID: 44913
Summary: Missing DSE opportunity when second store is done in
inline assembly
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: Scalar Optimizations
Assignee: unassignedb...@nondot.org
Reporter: gli...@google.com
CC: florian_h...@apple.com, llvm-bugs@lists.llvm.org,
llvm-bugzi...@jfbastien.com, vitalyb...@google.com
As reported by Daniel Colascione, Clang fails to remove the dead store in the
following program:
extern int foo(int* bar);
int bar()
{
int x = 5;
asm("nop\n\tnop\n\tnop" : "=m" (x));
return foo(&x);
}
see https://gcc.godbolt.org/z/c2fMNH (bad, clang) vs.
https://gcc.godbolt.org/z/a_biz5 (good, GCC).
This probably prevents it from deleting redundant initialization before
copy_from_user() in the Linux kernel.
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