[clang] [Clang] Diagnose nested inline asm variants (PR #232686)

[Oliver Hunt via cfe-commits]

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@@ -138,3 +138,7 @@ void test_W(int i) {
   // Codegen error
   __asm__("" : : "Ws"(i));
 }
+
+void test_nested_variants(long num) {
+  __asm__("{{movq $42, %0|}" : "=r"(num)); // expected-error{{nested variants found in inline assembly string}}
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ojhunt wrote:

So this diagnostic talks about nested variants but this testcase looks like it is an unterminated variant going wrong. Can you add tests that cover correctly terminated nested variants as well, so we can be sure that we are not only detecting invalid syntax, etc?

https://github.com/llvm/llvm-project/pull/232686