[const-prop] Handle MIR Rvalue::Aggregates

Author: wesleywiser

src/librustc_mir/transform/const_prop.rs

@@ -461,13 +461,13 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
 
         // if this isn't a supported operation, then return None
         match rvalue {
-            Rvalue::Aggregate(..) |
             Rvalue::NullaryOp(NullOp::Box, _) |
             Rvalue::Discriminant(..) => return None,
 
             Rvalue::Use(_) |
             Rvalue::Len(_) |
             Rvalue::Repeat(..) |
+            Rvalue::Aggregate(..) |
             Rvalue::Cast(..) |
             Rvalue::NullaryOp(..) |
             Rvalue::CheckedBinaryOp(..) |
@@ -560,6 +560,12 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
                     return None;
                 }
             }
+        } else if let Rvalue::Aggregate(_, operands) = rvalue {
+            // FIXME(wesleywiser): const eval will turn this into a `const Scalar(<ZST>)` that
+            // `SimplifyLocals` doesn't know it can remove.
+            if operands.len() == 0 {
+                return None;
+            }
         }
 
         self.use_ecx(source_info, |this| {

src/test/compile-fail/consts/const-err3.rs

@@ -14,6 +14,7 @@ fn main() {
     //~^ ERROR const_err
     let _e = [5u8][1];
     //~^ ERROR const_err
+    //~| ERROR this expression will panic at runtime
     black_box(b);
     black_box(c);
     black_box(d);

src/test/mir-opt/const_prop/aggregate.rs

@@ -0,0 +1,25 @@
+// compile-flags: -O
+
+fn main() {
+    let x = (0, 1, 2).1 + 0;
+}
+
+// END RUST SOURCE
+// START rustc.main.ConstProp.before.mir
+//  bb0: {
+//      ...
+//      _3 = (const 0i32, const 1i32, const 2i32);
+//      _2 = (_3.1: i32);
+//      _1 = Add(move _2, const 0i32);
+//      ...
+//  }
+// END rustc.main.ConstProp.before.mir
+// START rustc.main.ConstProp.after.mir
+//  bb0: {
+//      ...
+//      _3 = (const 0i32, const 1i32, const 2i32);
+//      _2 = const 1i32;
+//      _1 = Add(move _2, const 0i32);
+//      ...
+//  }
+// END rustc.main.ConstProp.after.mir

src/test/run-fail/overflowing-rsh-5.rs

@@ -2,6 +2,7 @@
 // compile-flags: -C debug-assertions
 
 #![warn(exceeding_bitshifts)]
+#![warn(const_err)]
 
 fn main() {
     let _n = 1i64 >> [64][0];

src/test/run-fail/overflowing-rsh-6.rs

@@ -2,6 +2,7 @@
 // compile-flags: -C debug-assertions
 
 #![warn(exceeding_bitshifts)]
+#![warn(const_err)]
 #![feature(const_indexing)]
 
 fn main() {

src/test/ui/consts/const-err2.rs

@@ -23,6 +23,7 @@ fn main() {
     //~^ ERROR const_err
     let _e = [5u8][1];
     //~^ ERROR index out of bounds
+    //~| ERROR this expression will panic at runtime
     black_box(a);
     black_box(b);
     black_box(c);

src/test/ui/consts/const-err2.stderr

@@ -34,5 +34,11 @@ error: index out of bounds: the len is 1 but the index is 1
 LL |     let _e = [5u8][1];
    |              ^^^^^^^^
 
-error: aborting due to 5 previous errors
+error: this expression will panic at runtime
+  --> $DIR/const-err2.rs:24:14
+   |
+LL |     let _e = [5u8][1];
+   |              ^^^^^^^^ index out of bounds: the len is 1 but the index is 1
+
+error: aborting due to 6 previous errors
 

src/test/ui/consts/const-err3.rs

@@ -23,6 +23,7 @@ fn main() {
     //~^ ERROR const_err
     let _e = [5u8][1];
     //~^ ERROR const_err
+    //~| ERROR this expression will panic at runtime
     black_box(a);
     black_box(b);
     black_box(c);

src/test/ui/consts/const-err3.stderr

@@ -34,5 +34,11 @@ error: index out of bounds: the len is 1 but the index is 1
 LL |     let _e = [5u8][1];
    |              ^^^^^^^^
 
-error: aborting due to 5 previous errors
+error: this expression will panic at runtime
+  --> $DIR/const-err3.rs:24:14
+   |
+LL |     let _e = [5u8][1];
+   |              ^^^^^^^^ index out of bounds: the len is 1 but the index is 1
+
+error: aborting due to 6 previous errors
 

src/test/ui/issues/issue-54348.rs

@@ -1,5 +1,7 @@
 fn main() {
     [1][0u64 as usize];
     [1][1.5 as usize]; //~ ERROR index out of bounds
+    //~| ERROR this expression will panic at runtime
     [1][1u64 as usize]; //~ ERROR index out of bounds
+    //~| ERROR this expression will panic at runtime
 }