[llvm-bugs] [Bug 45903] New: overrestrictive asm goto gotolabels limitations
via llvm-bugs
llvm-bugs at lists.llvm.org
Wed May 13 07:53:34 PDT 2020
https://bugs.llvm.org/show_bug.cgi?id=45903
Bug ID: 45903
Summary: overrestrictive asm goto gotolabels limitations
Product: clang
Version: 10.0
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: C
Assignee: unassignedclangbugs at nondot.org
Reporter: jacob at shuf.ro
CC: blitzrakete at gmail.com, dgregor at apple.com,
erik.pilkington at gmail.com, llvm-bugs at lists.llvm.org,
richard-llvm at metafoo.co.uk
First of all, I apologize if this is the wrong venue for this bug report.
The following does not compile, even though I believe it should:
---------------------------------------------------
cleanup_cb(*p1) {}
foo(int n) {
int cond;
if (({
asm goto("" ::"r"(cond) : : label0);
1;
}))
label0:;
int a[n];
if (({
asm goto("" ::"r"(cond) : : label1);
1;
}))
label1:;
}
main() {}
---------------------------------------------------
jshufro at 660:~/asmgoto$ clang-10 main.c
main.c:1:13: warning: type specifier missing, defaults to 'int'
[-Wimplicit-int]
cleanup_cb(*p1) {}
^
main.c:1:1: warning: type specifier missing, defaults to 'int' [-Wimplicit-int]
cleanup_cb(*p1) {}
^
main.c:1:18: warning: non-void function does not return a value [-Wreturn-type]
cleanup_cb(*p1) {}
^
main.c:3:1: warning: type specifier missing, defaults to 'int' [-Wimplicit-int]
foo(int n) {
^
main.c:7:9: error: cannot jump from this asm goto statement to one of its
possible targets
asm goto("" ::"r"(cond) : : label0);
^
main.c:18:3: note: possible target of asm goto statement
label1:;
^
main.c:12:7: note: jump bypasses initialization of variable length array
int a[n];
^
main.c:22:1: warning: type specifier missing, defaults to 'int'
[-Wimplicit-int]
main() {}
^
5 warnings and 1 error generated.
---------------------------------------------------
This is C-Reduced to be fairly minimal. Replacing the variable length array
with an __attribute__((cleanup)) variable causes a similar issue. It's worth
noting that the error is noting a possible target of asm goto that isn't listed
in the GoToLabels.
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