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! 🎉), 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\>

src/rustllvm/RustWrapper.cpp

@@ -426,6 +426,11 @@ extern "C" LLVMValueRef LLVMRustInlineAsm(LLVMTypeRef Ty, char *AsmString,
                              HasSideEffects, IsAlignStack, fromRust(Dialect)));
 }
 
+extern "C" bool LLVMRustInlineAsmVerify(LLVMTypeRef Ty,
+                                          char *Constraints) {
+  return InlineAsm::Verify(unwrap<FunctionType>(Ty), Constraints);
+}
+
 extern "C" void LLVMRustAppendModuleInlineAsm(LLVMModuleRef M, const char *Asm) {
   unwrap(M)->appendModuleInlineAsm(StringRef(Asm));
 }