Gate llvm.sideeffect under -Z insert-sideeffect

Author: sfanxiang

src/librustc/session/config.rs

@@ -1472,6 +1472,9 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         "which mangling version to use for symbol names"),
     binary_dep_depinfo: bool = (false, parse_bool, [TRACKED],
         "include artifacts (sysroot, crate dependencies) used during compilation in dep-info"),
+    insert_sideeffect: bool = (false, parse_bool, [TRACKED],
+        "fix undefined behavior when a thread doesn't eventually make progress \
+         (such as entering an empty infinite loop) by inserting llvm.sideeffect"),
 }
 
 pub fn default_lib_output() -> CrateType {

src/librustc_codegen_llvm/intrinsic.rs

@@ -726,8 +726,10 @@ impl IntrinsicCallMethods<'tcx> for Builder<'a, 'll, 'tcx> {
     }
 
     fn sideeffect(&mut self) {
-        let fnname = self.get_intrinsic(&("llvm.sideeffect"));
-        self.call(fnname, &[], None);
+        if self.tcx.sess.opts.debugging_opts.insert_sideeffect {
+            let fnname = self.get_intrinsic(&("llvm.sideeffect"));
+            self.call(fnname, &[], None);
+        }
     }
 
     fn va_start(&mut self, va_list: &'ll Value) -> &'ll Value {

src/librustc_codegen_ssa/mir/block.rs

@@ -157,13 +157,15 @@ impl<'a, 'tcx> TerminatorCodegenHelper<'a, 'tcx> {
         bx: &mut Bx,
         targets: &[mir::BasicBlock],
     ) {
-        if targets.iter().any(|target| {
-            *target <= *self.bb
-                && target
-                    .start_location()
-                    .is_predecessor_of(self.bb.start_location(), mir)
-        }) {
-            bx.sideeffect();
+        if bx.tcx().sess.opts.debugging_opts.insert_sideeffect {
+            if targets.iter().any(|target| {
+                *target <= *self.bb
+                    && target
+                        .start_location()
+                        .is_predecessor_of(self.bb.start_location(), mir)
+            }) {
+                bx.sideeffect();
+            }
         }
     }
 }

src/test/codegen/alloc-optimisation.rs

@@ -7,8 +7,7 @@
 pub fn alloc_test(data: u32) {
     // CHECK-LABEL: @alloc_test
     // CHECK-NEXT: start:
-    // CHECK-NOT: alloc
-    // CHECK: ret void
+    // CHECK-NEXT: ret void
     let x = Box::new(data);
     drop(x);
 }

src/test/codegen/dealloc-no-unwind.rs

@@ -17,7 +17,7 @@ impl Drop for A {
 pub fn a(a: Box<i32>) {
     // CHECK-LABEL: define void @a
     // CHECK: call void @__rust_dealloc
-    // CHECK: call void @foo
+    // CHECK-NEXT: call void @foo
     let _a = A;
     drop(a);
 }

src/test/codegen/issue-34947-pow-i32.rs

@@ -6,11 +6,8 @@
 #[no_mangle]
 pub fn issue_34947(x: i32) -> i32 {
     // CHECK: mul
-    // CHECK-NOT: br label
-    // CHECK: mul
-    // CHECK-NOT: br label
-    // CHECK: mul
-    // CHECK-NOT: br label
-    // CHECK: ret
+    // CHECK-NEXT: mul
+    // CHECK-NEXT: mul
+    // CHECK-NEXT: ret
     x.pow(5)
 }

src/test/codegen/issue-45222.rs

@@ -1,9 +1,3 @@
-// ignore-test
-
-// FIXME:
-// LLVM can't optimize some loops with a large number of iterations because of
-// @llvm.sideeffect() (see also #59546)
-
 // compile-flags: -O
 // ignore-debug: the debug assertions get in the way
 

src/test/codegen/naked-functions.rs

@@ -1,3 +1,5 @@
+// ignore-tidy-linelength
+
 // compile-flags: -C no-prepopulate-passes
 
 #![crate_type = "lib"]
@@ -51,27 +53,27 @@ pub fn naked_with_args_and_return(a: isize) -> isize {
 #[naked]
 pub fn naked_recursive() {
     // CHECK-NEXT: {{.+}}:
-    // CHECK: call void @naked_empty()
+    // CHECK-NEXT: call void @naked_empty()
 
     // FIXME(#39685) Avoid one block per call.
     // CHECK-NEXT: br label %bb1
     // CHECK: bb1:
 
     naked_empty();
 
-    // CHECK: %{{[0-9]+}} = call i{{[0-9]+}} @naked_with_return()
+    // CHECK-NEXT: %{{[0-9]+}} = call i{{[0-9]+}} @naked_with_return()
 
     // FIXME(#39685) Avoid one block per call.
     // CHECK-NEXT: br label %bb2
     // CHECK: bb2:
 
-    // CHECK: %{{[0-9]+}} = call i{{[0-9]+}} @naked_with_args_and_return(i{{[0-9]+}} %{{[0-9]+}})
+    // CHECK-NEXT: %{{[0-9]+}} = call i{{[0-9]+}} @naked_with_args_and_return(i{{[0-9]+}} %{{[0-9]+}})
 
     // FIXME(#39685) Avoid one block per call.
     // CHECK-NEXT: br label %bb3
     // CHECK: bb3:
 
-    // CHECK: call void @naked_with_args(i{{[0-9]+}} %{{[0-9]+}})
+    // CHECK-NEXT: call void @naked_with_args(i{{[0-9]+}} %{{[0-9]+}})
 
     // FIXME(#39685) Avoid one block per call.
     // CHECK-NEXT: br label %bb4

src/test/codegen/non-terminate/infinite-loop-1.rs

@@ -1,4 +1,4 @@
-// compile-flags: -C opt-level=3
+// compile-flags: -C opt-level=3 -Z insert-sideeffect
 
 #![crate_type = "lib"]
 

src/test/codegen/non-terminate/infinite-loop-2.rs

@@ -1,4 +1,4 @@
-// compile-flags: -C opt-level=3
+// compile-flags: -C opt-level=3 -Z insert-sideeffect
 
 #![crate_type = "lib"]