https://bugs.llvm.org/show_bug.cgi?id=43160
Bug ID: 43160
Summary: [deadargelim] removes "this" from x86_thiscallcc
Product: libraries
Version: 8.0
Hardware: PC
OS: Windows NT
Status: NEW
Severity: normal
Priority: P
Component: Interprocedural Optimizations
Assignee: unassignedb...@nondot.org
Reporter: cfswo...@gmail.com
CC: llvm-bugs@lists.llvm.org
This is very similar to bug 38487; my test case in fact is slightly modified
from there.
In this case, I've modified the F::k function to avoid relying on the `this`
pointer. -deadargelim removes `this`, but leaves the calling convention set to
x86_thiscallcc, so the second argument (whatever that may be) ends up shoved
into ECX.
When combined with inalloca, the following fatal error is generated:
cannot use inalloca attribute on a register parameter
However, inalloca aside, removing `this` from any calling convention that
treats `this` specially does break that calling convention. The calling
convention should either be changed (to fastcc?) or the functions with these
special calling conventions should simply have their `this` pointer left alone.
// x.cpp
// clang++ -target i386-pc-windows-msvc -O3 -c x.cpp
struct Y
{
int i;
Y();
Y(const Y&);
};
void h(Y y);
namespace {
struct F {
void k(Y y) {
y.i = 0;
h(y);
}
};
}
void foo()
{
F f;
Y y;
f.k(y);
}
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