Auto merge of #54568 - levex:issue-54130, r=nagisa

codegen_llvm: check inline assembly constraints with LLVM

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Hey all,

As issue #54130 highlights, constraints are not checked and passing bad constraints to LLVM can crash it since a `Verify()` call is placed inside an assertion (see: `src/llvm/lib/IR/InlineAsm.cpp:39`).

As this is my first PR to the Rust compiler (woot! :tada:), there might be better ways of achieving this result. In particular, I am not too happy about generating an error in codegen; it would be much nicer if we did it earlier. However, @rkruppe [noted on IRC](https://botbot.me/mozilla/rustc/2018-09-25/?msg=104791581&page=1) that this should be fine for an unstable feature and a much better solution than the _status quo_, which is an ICE.

Thanks!
--->%---

LLVM provides a way of checking whether the constraints and the actual
inline assembly make sense. This commit introduces a check before
emitting code for the inline assembly. If LLVM rejects the inline
assembly (or its constraints), then the compiler emits an error E0668
("malformed inline assembly").

Fixes: #54130
Signed-off-by: Levente Kurusa \<lkurusa@acm.org\>

1 files changed, 5 insertions, 1 deletions

diff --git a/src/librustc_codegen_llvm/mir/statement.rs b/src/librustc_codegen_llvm/mir/statement.rs
index b4eb7615f98..6bd41bfe16f 100644
--- a/src/librustc_codegen_llvm/mir/statement.rs
+++ b/src/librustc_codegen_llvm/mir/statement.rs
@@ -86,7 +86,11 @@ impl FunctionCx<'a, 'll, 'tcx> {
                     self.codegen_operand(&bx, input).immediate()
                 }).collect();
 
-                asm::codegen_inline_asm(&bx, asm, outputs, input_vals);
+                let res = asm::codegen_inline_asm(&bx, asm, outputs, input_vals);
+                if !res {
+                    span_err!(bx.sess(), statement.source_info.span, E0668,
+                              "malformed inline assembly");
+                }
                 bx
             }
             mir::StatementKind::FakeRead(..) |