Ignore intrinsic calls in cross-crate-inlining cost model

Author: saethlin

compiler/rustc_mir_transform/src/cross_crate_inline.rs

@@ -135,7 +135,16 @@ impl<'tcx> Visitor<'tcx> for CostChecker<'_, 'tcx> {
                     }
                 }
             }
-            TerminatorKind::Call { unwind, .. } => {
+            TerminatorKind::Call { ref func, unwind, .. } => {
+                // We track calls because they make our function not a leaf (and in theory, the
+                // number of calls indicates how likely this function is to perturb other CGUs).
+                // But intrinsics don't have a body that gets assigned to a CGU, so they are
+                // ignored.
+                if let Some((fn_def_id, _)) = func.const_fn_def()
+                    && self.tcx.has_attr(fn_def_id, sym::rustc_intrinsic)
+                {
+                    return;
+                }
                 self.calls += 1;
                 if let UnwindAction::Cleanup(_) = unwind {
                     self.landing_pads += 1;

tests/assembly-llvm/breakpoint.rs

@@ -9,6 +9,7 @@
 // CHECK-LABEL: use_bp
 // aarch64: brk #0xf000
 // x86_64: int3
+#[inline(never)]
 pub fn use_bp() {
     core::arch::breakpoint();
 }

tests/assembly-llvm/simd/reduce-fadd-unordered.rs

@@ -16,6 +16,7 @@ use std::simd::*;
 // It would emit about an extra fadd, depending on the architecture.
 
 // CHECK-LABEL: reduce_fadd_negative_zero
+#[inline(never)]
 pub unsafe fn reduce_fadd_negative_zero(v: f32x4) -> f32 {
     // x86_64: addps
     // x86_64-NEXT: movshdup

tests/codegen-llvm/cross-crate-inlining/auxiliary/leaf.rs

@@ -18,3 +18,8 @@ pub fn stem_fn() -> String {
 fn inner() -> String {
     String::from("test")
 }
+
+// This function's optimized MIR contains a call, but it is to an intrinsic.
+pub fn leaf_with_intrinsic(a: &[u64; 2], b: &[u64; 2]) -> bool {
+    a == b
+}

tests/codegen-llvm/cross-crate-inlining/leaf-inlining.rs

@@ -18,3 +18,10 @@ pub fn stem_outer() -> String {
     // CHECK: call {{.*}}stem_fn
     leaf::stem_fn()
 }
+
+// Check that we inline functions that call intrinsics
+#[no_mangle]
+pub fn leaf_with_intrinsic_outer(a: &[u64; 2], b: &[u64; 2]) -> bool {
+    // CHECK-NOT: call {{.*}}leaf_with_intrinsic
+    leaf::leaf_with_intrinsic(a, b)
+}

tests/codegen-llvm/default-visibility.rs

@@ -32,6 +32,7 @@ pub static tested_symbol: [u8; 6] = *b"foobar";
 // INTERPOSABLE: @{{.*}}default_visibility{{.*}}tested_symbol{{.*}} = constant
 // DEFAULT:      @{{.*}}default_visibility{{.*}}tested_symbol{{.*}} = constant
 
+#[inline(never)]
 pub fn do_memcmp(left: &[u8], right: &[u8]) -> i32 {
     left.cmp(right) as i32
 }