https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114923
Bug ID: 114923
Summary: gcc ignores escaping pointer and applies invalid
optimization
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: nfxjfg at googlemail dot com
Target Milestone: ---
Created attachment 58088
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=58088&action=edit
Test case
In this test case, the pointer to a stack-allocated variable is passed to a
volatile variable. That means the pointer definitely escapes. But the compiler
seems to assume that the memory can't change, and returns the initialization
value of the buf variable.
I tried multiple variations of this. Sometimes it generates the correct code,
even though the situation is exactly the same. A call to an external function
often fixes it, but sometimes not (could not produce a reduced test case of the
latter).
This is reduced from some real-word code. The first register access passes the
memory pointer to the hardware, the second access starts the DMA. In the
real-world code there was some more stuff such as waiting for the DMA to
finish, but it doesn't matter for code generation. The code started to fail
after a DMA buffer was moved from a global variable to the stack.
Originally experienced on 12.2.0 / riscv32-unknown-elf, but on godlbolt I can
reproduce it with trunk and some other architectures.
