https://llvm.org/bugs/show_bug.cgi?id=26776
Bug ID: 26776
Summary: Arguments containing allocas for functions that use
inalloca need to be evaluated first
Product: clang
Version: unspecified
Hardware: PC
OS: Windows NT
Status: NEW
Severity: normal
Priority: P
Component: LLVM Codegen
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
Consider:
int x = 10;
struct A { A(); ~A(); };
void foo(A, void*, A);
int main() {
foo(A(), (++x, _alloca(x)), A());
}
Function call arguments need to live on the top of the stack, that's just how
they work. alloca, however, lets the programmer allocate stack memory from an
expression, which can break the call frame. MSVC overcomes this problem by
evaluating arguments that contain calls to alloca before the outermost call
expression. This is legal because argument evaluation order is unsequenced. We
should do the same thing in Clang at some point.
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