void added a comment. In D60943#1474926 <https://reviews.llvm.org/D60943#1474926>, @rsmith wrote:
> In D60943#1474899 <https://reviews.llvm.org/D60943#1474899>, @void wrote: > > > Here's the motivating bug report: > > https://bugs.llvm.org/show_bug.cgi?id=41027 > > > Thanks, that's illuminating. OK, if we want to support that code, then > there's really not much validation we can do in the frontend for constraints > that require immediate constants. Is `"n"` really special in this regard, or > is it just the first one that we've encountered? I think it's just the first one we've encountered. There could be other constraints which require immediates, but they're probably target-specific. E.g. `e` and `K` for x86. >> In general, I agree with you that diagnostics shouldn't depend on >> optimization levels, but inline assembly subverts this paradigm because it >> was originally a gcc extension. :-( > > There is a question of how much weird stuff we should accept in the name of > GCC compatibility. In this case, the fact that the frontend rejects seems > like the tip of an iceberg: the code in the PR is also relying on the control > flow of the `&&` inside the `if` to be emitted in a very particular way (or > to be optimized to that form), and for dead-code elimination to be considered > and to actually fire, and probably more things besides. Do we at least still > produce a nice diagnostic if the value ends up not being a constant? It does, but for the wrong line: [morbo@fawn:llvm] cat bad.c static __attribute__((always_inline)) void outl(unsigned port, unsigned data) { asm volatile("outl %0,%w1" : : "a"(data), "n"(port)); } void f(unsigned port) { outl(port, 1); } [morbo@fawn:llvm] ./llvm.opt.install/bin/clang -c bad.c bad.c:2:16: error: constraint 'n' expects an integer constant expression asm volatile("outl %0,%w1" : : "a"(data), "n"(port)); ^ 1 error generated. I'll need to modify the LLVM patch to output the correct location. Repository: rC Clang CHANGES SINCE LAST ACTION https://reviews.llvm.org/D60943/new/ https://reviews.llvm.org/D60943 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
