[clang] Alias cc modifier to c (#127719)

https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#GenericOperandmodifiers
provides the `c` and `cc` modifiers. GCC 15 introduces the `cc` modifier
which does the same as `c`. This patch lets Clang handle this for
compatibility.

Author: PiJoules

clang/docs/ReleaseNotes.rst

@@ -109,6 +109,8 @@ C23 Feature Support
 Non-comprehensive list of changes in this release
 -------------------------------------------------
 
+- Support parsing the `cc` operand modifier and alias it to the `c` modifier (#GH127719).
+
 New Compiler Flags
 ------------------
 

clang/lib/AST/Stmt.cpp

@@ -708,6 +708,13 @@ unsigned GCCAsmStmt::AnalyzeAsmString(SmallVectorImpl<AsmStringPiece>&Pieces,
         DiagOffs = CurPtr-StrStart-1;
         return diag::err_asm_invalid_escape;
       }
+
+      // Specifically handle `cc` which we will alias to `c`.
+      // Note this is the only operand modifier that exists which has two
+      // characters.
+      if (EscapedChar == 'c' && *CurPtr == 'c')
+        CurPtr++;
+
       EscapedChar = *CurPtr++;
     }
 

clang/test/AST/cc-modifier.cpp

@@ -0,0 +1,10 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu  %s -verify
+// expected-no-diagnostics
+
+void func();
+void func2();
+
+bool func3() {                                                                                               
+  __asm__("%cc0 = %c1" : : "X"(func), "X"(func2));
+  return func2 == func;
+}                                                                                                                    

clang/test/CodeGen/asm.c

@@ -284,3 +284,9 @@ void *t33(void *ptr)
   // CHECK: @t33
   // CHECK: %1 = call ptr asm "lea $1, $0", "=r,p,~{dirflag},~{fpsr},~{flags}"(ptr %0)
 }
+
+void t34(void) {
+  __asm__ volatile("T34 CC NAMED MODIFIER: %cc[input]" :: [input] "i" (4));
+  // CHECK: @t34()
+  // CHECK: T34 CC NAMED MODIFIER: ${0:c}
+}