Translate MIR Repeat (arrays)

[nagisa]

r? @nikomatsakis

I went ahead and replaced repeat count with a Constant, because it cannot be non-constant to the best of my knowledge.

[nagisa]

Also, probably fixes #29577?

[dotdash]

AFAICT let x = [0; 5*5] would mean that the repeat is an operand since the constant expression has not been evaluated yet.

[nagisa]

Ah, okay. I’ve reverted the Constant part.

[nikomatsakis]

This looks good --- I actually think a constant might have been the right choice here though.

[nikomatsakis]

(We would have to use the const_eval to convert the expression to a constant when building MIR though, not sure what your now-reverted patch was doing.)

[nikomatsakis]

@nagisa do you still have the constant part of your patch somewhere I could see it?

[nagisa]

@nikomatsakis This is about it (applied over current commit).

diff --git a/src/librustc_mir/build/expr/as_rvalue.rs b/src/librustc_mir/build/expr/as_rvalue.rs
index 23ca221..e351215 100644
--- a/src/librustc_mir/build/expr/as_rvalue.rs
+++ b/src/librustc_mir/build/expr/as_rvalue.rs
@@ -44,8 +44,8 @@ impl<'a,'tcx> Builder<'a,'tcx> {
             }
             ExprKind::Repeat { value, count } => {
                 let value_operand = unpack!(block = this.as_operand(block, value));
-                let count_operand = unpack!(block = this.as_operand(block, count));
-                block.and(Rvalue::Repeat(value_operand, count_operand))
+                let count = this.as_constant(count);
+                block.and(Rvalue::Repeat(value_operand, count))
             }
             ExprKind::Borrow { region, borrow_kind, arg } => {
                 let arg_lvalue = unpack!(block = this.as_lvalue(block, arg));
diff --git a/src/librustc_mir/repr.rs b/src/librustc_mir/repr.rs
index 89b1afa..4ab08f9 100644
--- a/src/librustc_mir/repr.rs
+++ b/src/librustc_mir/repr.rs
@@ -546,7 +546,7 @@ pub enum Rvalue<'tcx> {
     Use(Operand<'tcx>),

     // [x; 32]
-    Repeat(Operand<'tcx>, Operand<'tcx>),
+    Repeat(Operand<'tcx>, Constant<'tcx>),

     // &x or &mut x
     Ref(Region, BorrowKind, Lvalue<'tcx>),
diff --git a/src/librustc_mir/visit.rs b/src/librustc_mir/visit.rs
index b4d6075..9f214af 100644
--- a/src/librustc_mir/visit.rs
+++ b/src/librustc_mir/visit.rs
@@ -134,7 +134,7 @@ pub trait Visitor<'tcx> {

             Rvalue::Repeat(ref value, ref len) => {
                 self.visit_operand(value);
-                self.visit_operand(len);
+                self.visit_constant(len);
             }

             Rvalue::Ref(r, bk, ref path) => {
diff --git a/src/librustc_trans/trans/mir/rvalue.rs b/src/librustc_trans/trans/mir/rvalue.rs
index f3515c0..218edc2 100644
--- a/src/librustc_trans/trans/mir/rvalue.rs
+++ b/src/librustc_trans/trans/mir/rvalue.rs
@@ -51,9 +51,9 @@ impl<'bcx, 'tcx> MirContext<'bcx, 'tcx> {

             mir::Rvalue::Repeat(ref elem, ref count) => {
                 let elem = self.trans_operand(bcx, elem);
-                let size = self.trans_operand(bcx, count);
+                let size = self.trans_constant(bcx, count);
                 let base = expr::get_dataptr(bcx, lldest);
-                tvec::iter_vec_raw(bcx, base, elem.ty, size.llval, |b, vref, _| {
+                tvec::iter_vec_raw(bcx, base, elem.ty, size, |b, vref, _| {
                     build::Store(b, elem.llval, vref);
                     b
                 })

[nikomatsakis]

@nagisa ok, yeah, I think we should change it to a constant then, since indeed the value must be a compile-time constant

[nagisa]

@nikomatsakis updated. @dotdash’s case also seems to work without any changes and const-eval in MIR may be expanded as necessary in as_constant.

[nikomatsakis]

@bors r+ thanks!

[bors]

📌 Commit db89a75 has been approved by nikomatsakis

[bors]

⌛ Testing commit db89a75 with merge 94f8304...

[bors]

💔 Test failed - auto-linux-64-x-android-t

[nagisa]

@nikomatsakis re-review, please.

[nikomatsakis]

@bors r+

Thanks!

[bors]

📌 Commit e4e880d has been approved by nikomatsakis

[bors]

⌛ Testing commit e4e880d with merge 35decad...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-debug-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-linux-cross-opt, auto-linux-musl-64-opt, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-opt

[ttemel]

Testing commit db89a75 with merge 94f8304...