Rollup merge of #143720 - scottmcm:rvalue-always-operand, r=lcnr

Allow `Rvalue::Repeat` to return true in `rvalue_creates_operand` too

The conversation in https://github.com/rust-lang/rust/pull/143502#discussion_r2189410911 made be realize how easy this is to handle, since the only possibilty is ZSTs -- everything else ends up with the destination being `LocalKind::Memory` and thus doesn't call `codegen_rvalue_operand` at all.

This gets us perilously close to a world where `rvalue_creates_operand` only ever returns true.  (See rust-lang/rust#143860 for more.)

2 files changed, 56 insertions, 0 deletions

diff --git a/tests/codegen/repeat-operand-zero-len.rs b/tests/codegen/repeat-operand-zero-len.rs
new file mode 100644
index 00000000000..b4cec42a07c
--- /dev/null
+++ b/tests/codegen/repeat-operand-zero-len.rs
@@ -0,0 +1,28 @@
+//@ compile-flags: -Copt-level=1 -Cno-prepopulate-passes
+
+// This test is here to hit the `Rvalue::Repeat` case in `codegen_rvalue_operand`.
+// It only applies when the resulting array is a ZST, so the test is written in
+// such a way as to keep MIR optimizations from seeing that fact and removing
+// the local and statement altogether. (At the time of writing, no other codegen
+// test hit that code path, nor did a stage 2 build of the compiler.)
+
+#![crate_type = "lib"]
+
+#[repr(transparent)]
+pub struct Wrapper<T, const N: usize>([T; N]);
+
+// CHECK-LABEL: define {{.+}}do_repeat{{.+}}(i32 noundef %x)
+// CHECK-NEXT: start:
+// CHECK-NOT: alloca
+// CHECK-NEXT: ret void
+#[inline(never)]
+pub fn do_repeat<T: Copy, const N: usize>(x: T) -> Wrapper<T, N> {
+    Wrapper([x; N])
+}
+
+// CHECK-LABEL: @trigger_repeat_zero_len
+#[no_mangle]
+pub fn trigger_repeat_zero_len() -> Wrapper<u32, 0> {
+    // CHECK: call void {{.+}}do_repeat{{.+}}(i32 noundef 4)
+    do_repeat(4)
+}
diff --git a/tests/codegen/repeat-operand-zst-elem.rs b/tests/codegen/repeat-operand-zst-elem.rs
new file mode 100644
index 00000000000..c3637759afa
--- /dev/null
+++ b/tests/codegen/repeat-operand-zst-elem.rs
@@ -0,0 +1,28 @@
+//@ compile-flags: -Copt-level=1 -Cno-prepopulate-passes
+
+// This test is here to hit the `Rvalue::Repeat` case in `codegen_rvalue_operand`.
+// It only applies when the resulting array is a ZST, so the test is written in
+// such a way as to keep MIR optimizations from seeing that fact and removing
+// the local and statement altogether. (At the time of writing, no other codegen
+// test hit that code path, nor did a stage 2 build of the compiler.)
+
+#![crate_type = "lib"]
+
+#[repr(transparent)]
+pub struct Wrapper<T, const N: usize>([T; N]);
+
+// CHECK-LABEL: define {{.+}}do_repeat{{.+}}()
+// CHECK-NEXT: start:
+// CHECK-NOT: alloca
+// CHECK-NEXT: ret void
+#[inline(never)]
+pub fn do_repeat<T: Copy, const N: usize>(x: T) -> Wrapper<T, N> {
+    Wrapper([x; N])
+}
+
+// CHECK-LABEL: @trigger_repeat_zst_elem
+#[no_mangle]
+pub fn trigger_repeat_zst_elem() -> Wrapper<(), 8> {
+    // CHECK: call void {{.+}}do_repeat{{.+}}()
+    do_repeat(())
+}