AArch64: add __builtin_arm_trap

It's useful to provide an indicator code with the trap, which the generic
__builtin_trap can't do. asm("brk #N") is an option, but following that with a
__builtin_unreachable() leads to two traps when the compiler doesn't know the
block can't return. So compiler support like this is useful.

Author: TNorthover

clang/docs/LanguageExtensions.rst

@@ -3443,6 +3443,21 @@ Query for this feature with ``__has_builtin(__builtin_debugtrap)``.
 
 Query for this feature with ``__has_builtin(__builtin_trap)``.
 
+``__builtin_arm_trap``
+------------------
+
+``__builtin_arm_trap`` is an AArch64 extension to ``__builtin_trap`` which also accepts a compile-time constant value, encoded directly into the trap instruction for later inspection.
+
+**Syntax**:
+
+.. code-block:: c++
+
+    __builtin_arm_trap(const unsigned short payload)
+
+**Description**
+
+``__builtin_arm_trap`` is lowered to the ``llvm.aarch64.break`` builtin, and then to ``brk #payload``.
+
 ``__builtin_nondeterministic_value``
 ------------------------------------
 

clang/include/clang/Basic/BuiltinsAArch64.def

@@ -50,6 +50,9 @@ BUILTIN(__builtin_arm_wfi, "v", "")
 BUILTIN(__builtin_arm_sev, "v", "")
 BUILTIN(__builtin_arm_sevl, "v", "")
 
+// Like __builtin_trap but provide an 16-bit immediate reason code (which goes into `brk #N`).
+BUILTIN(__builtin_arm_trap, "vUIs", "nr")
+
 // CRC32
 TARGET_BUILTIN(__builtin_arm_crc32b, "UiUiUc", "nc", "crc")
 TARGET_BUILTIN(__builtin_arm_crc32cb, "UiUiUc", "nc", "crc")

clang/lib/CodeGen/CGBuiltin.cpp

@@ -10686,6 +10686,12 @@ Value *CodeGenFunction::EmitAArch64BuiltinExpr(unsigned BuiltinID,
     return Builder.CreateCall(F, llvm::ConstantInt::get(Int32Ty, HintID));
   }
 
+  if (BuiltinID == clang::AArch64::BI__builtin_arm_trap) {
+    Function *F = CGM.getIntrinsic(Intrinsic::aarch64_break);
+    llvm::Value *Arg = EmitScalarExpr(E->getArg(0));
+    return Builder.CreateCall(F, Builder.CreateZExt(Arg, CGM.Int32Ty));
+  }
+
   if (BuiltinID == clang::AArch64::BI__builtin_arm_get_sme_state) {
     // Create call to __arm_sme_state and store the results to the two pointers.
     CallInst *CI = EmitRuntimeCall(CGM.CreateRuntimeFunction(

clang/test/CodeGen/builtins-arm64.c

@@ -156,4 +156,10 @@ int rndrrs(uint64_t *__addr) {
   return __builtin_arm_rndrrs(__addr);
 }
 
+// CHECK-LABEL: @trap(
+// CHECK: call void @llvm.aarch64.break(i32 42)
+void trap() {
+  __builtin_arm_trap(42);
+}
+
 // CHECK: ![[M0]] = !{!"1:2:3:4:5"}

clang/test/Sema/builtins-arm64.c

@@ -29,3 +29,12 @@ void test_prefetch(void) {
   __builtin_arm_prefetch(0, 0, 0, 2, 0); // expected-error-re {{argument value {{.*}} is outside the valid range}}
   __builtin_arm_prefetch(0, 0, 0, 0, 2); // expected-error-re {{argument value {{.*}} is outside the valid range}}
 }
+
+void test_trap(short s, unsigned short us) {
+  __builtin_arm_trap(42);
+  __builtin_arm_trap(65535);
+  __builtin_arm_trap(-1);
+  __builtin_arm_trap(65536); // expected-warning {{implicit conversion from 'int' to 'unsigned short' changes value from 65536 to 0}}
+  __builtin_arm_trap(s); // expected-error {{argument to '__builtin_arm_trap' must be a constant integer}}
+  __builtin_arm_trap(us); // expected-error {{argument to '__builtin_arm_trap' must be a constant integer}}
+}