AArch64: add __builtin_arm_trap

[TNorthover]

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.

[llvmbot]

@llvm/pr-subscribers-backend-aarch64
@llvm/pr-subscribers-clang

@llvm/pr-subscribers-clang-codegen

Author: Tim Northover (TNorthover)

Changes

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.

---

Full diff: https://github.com/llvm/llvm-project/pull/85054.diff

4 Files Affected:

• (modified) clang/include/clang/Basic/BuiltinsAArch64.def (+3)
• (modified) clang/lib/CodeGen/CGBuiltin.cpp (+6)
• (modified) clang/test/CodeGen/builtins-arm64.c (+6)
• (modified) clang/test/Sema/builtins-arm64.c (+9)

diff --git a/clang/include/clang/Basic/BuiltinsAArch64.def b/clang/include/clang/Basic/BuiltinsAArch64.def
index b5cbe90c8fd6a3..cf8711c6eaee37 100644
--- a/clang/include/clang/Basic/BuiltinsAArch64.def
+++ b/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")
diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp
index 93ab465079777b..528a13fb275124 100644
--- a/clang/lib/CodeGen/CGBuiltin.cpp
+++ b/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(
diff --git a/clang/test/CodeGen/builtins-arm64.c b/clang/test/CodeGen/builtins-arm64.c
index 05ea1c719edff3..8bd68d9ceb48ec 100644
--- a/clang/test/CodeGen/builtins-arm64.c
+++ b/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"}
diff --git a/clang/test/Sema/builtins-arm64.c b/clang/test/Sema/builtins-arm64.c
index e711121f7260ff..f094162b3aadc9 100644
--- a/clang/test/Sema/builtins-arm64.c
+++ b/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}}
+}
\ No newline at end of file

[aemerson]

LGTM.

[DanielKristofKiss]

Maybe a line or two in the clang/docs/LanguageExtensions.rst would be useful.

[TNorthover]

Thanks. Good idea on the docs, I've added some wording and pushed the change (4299c72)