Such jumps are not allowed by GCC and allowing them
can lead to situations where we jumps into unevaluated
statements.
Fixes#63682
Reviewed By: aaron.ballman, #clang-language-wg
Differential Revision: https://reviews.llvm.org/D154696
The current behavior of JumpScopeChecker::VerifyIndirectOrAsmJumps was
to cross validate the scope of every jumping statement (goto, asm goto)
against the scope of every label (even if the label was not even a
possible target of the asm goto).
When we have multiple asm goto's with unique targets, we could trigger
false positive build errors complaining that labels that weren't even in
the asm goto's label list could not be jumped to. Example:
error: cannot jump from this asm goto statement to one of its possible targets
asm goto(""::::foo);
note: possible target of asm goto statement
bar:
^
Fixes: https://github.com/ClangBuiltLinux/linux/issues/1886
Reviewed By: void, jyu2, rjmccall
Differential Revision: https://reviews.llvm.org/D155342
Such jumps are not allowed by GCC and allowing them
can lead to situations where we jumps into unevaluated
statements.
Fixes#63682
Reviewed By: aaron.ballman, #clang-language-wg
Differential Revision: https://reviews.llvm.org/D154696
Summary:
Clang's "asm goto" feature didn't initially support outputs constraints. That
was the same behavior as gcc's implementation. The decision by gcc not to
support outputs was based on a restriction in their IR regarding terminators.
LLVM doesn't restrict terminators from returning values (e.g. 'invoke'), so
it made sense to support this feature.
Output values are valid only on the 'fallthrough' path. If an output value's used
on an indirect branch, then it's 'poisoned'.
In theory, outputs *could* be valid on the 'indirect' paths, but it's very
difficult to guarantee that the original semantics would be retained. E.g.
because indirect labels could be used as data, we wouldn't be able to split
critical edges in situations where two 'callbr' instructions have the same
indirect label, because the indirect branch's destination would no longer be
the same.
Reviewers: jyknight, nickdesaulniers, hfinkel
Reviewed By: jyknight, nickdesaulniers
Subscribers: MaskRay, rsmith, hiraditya, llvm-commits, cfe-commits, craig.topper, rnk
Tags: #clang, #llvm
Differential Revision: https://reviews.llvm.org/D69876
This reverts commit 954ec09aed4f2be04bb5f4e10dbb4ea8bd19ef9a.
Reverting due to test failures as requested by Jennifer Yu.
Conflicts:
clang/test/CodeGen/asm-goto.c
llvm-svn: 362106
Syntax:
asm [volatile] goto ( AssemblerTemplate
:
: InputOperands
: Clobbers
: GotoLabels)
https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html
New llvm IR is "callbr" for inline asm goto instead "call" for inline asm
For:
asm goto("testl %0, %0; jne %l1;" :: "r"(cond)::label_true, loop);
IR:
callbr void asm sideeffect "testl $0, $0; jne ${1:l};", "r,X,X,~{dirflag},~{fpsr},~{flags}"(i32 %0, i8* blockaddress(@foo, %label_true), i8* blockaddress(@foo, %loop)) #1
to label %asm.fallthrough [label %label_true, label %loop], !srcloc !3
asm.fallthrough:
Compiler need to generate:
1> a dummy constarint 'X' for each label.
2> an unique fallthrough label for each asm goto stmt " asm.fallthrough%number".
Diagnostic
1> duplicate asm operand name are used in output, input and label.
2> goto out of scope.
llvm-svn: 362045
