Fix GCC-style asm %= unique ID translation to LLVM ${:uid}

gen/asm-gcc.cpp

@@ -36,7 +36,10 @@ std::string translateTemplate(GccAsmStatement *stmt) {
       result += "$$"; // escape for LLVM: $ => $$
       break;
     case '%':
-      if (i < N - 1 && insn[i + 1] == '%') { // unescape for LLVM: %% => %
+      if (i < N - 1 && insn[i + 1] == '=') { // unique ID: %= => ${:uid}
+        result += "${:uid}";
+        ++i;
+      } else if (i < N - 1 && insn[i + 1] == '%') { // unescape for LLVM: %% => %
         result += '%';
         ++i;
       } else {

tests/codegen/asm_gcc_unique_id.d

@@ -0,0 +1,35 @@
+// Tests that GCC-style asm %= (unique ID) is correctly translated to LLVM ${:uid}
+// which generates unique labels for each asm statement.
+// See: https://github.com/ldc-developers/ldc/issues/4294
+
+// REQUIRES: target_X86
+
+// RUN: %ldc -mtriple=x86_64-linux-gnu -output-s -of=%t.s %s
+// RUN: FileCheck %s < %t.s
+
+// Two functions with identical asm that use %= should get different label numbers.
+// The ${:uid} mechanism in LLVM generates sequential numbers (0, 1, 2, ...).
+
+int func1() {
+    int result;
+    // CHECK-LABEL: func1
+    // CHECK: loop_[[ID1:[0-9]+]]:
+    // CHECK: jmp loop_[[ID1]]
+    asm {
+        "xorl %0, %0\n\tloop_%=:\n\tincl %0\n\tjmp loop_%="
+        : "=r" (result);
+    }
+    return result;
+}
+
+int func2() {
+    int result;
+    // CHECK-LABEL: func2
+    // CHECK: loop_[[ID2:[0-9]+]]:
+    // CHECK: jmp loop_[[ID2]]
+    asm {
+        "xorl %0, %0\n\tloop_%=:\n\tincl %0\n\tjmp loop_%="
+        : "=r" (result);
+    }
+    return result;
+}