Auto merge of #107921 - cjgillot:codegen-overflow-check, r=tmiasko

Make codegen choose whether to emit overflow checks

ConstProp and DataflowConstProp currently have a specific code path not to propagate constants when they overflow. This is meant to have the correct behaviour when inlining from a crate with overflow checks (like `core`) into a crate compiled without.

This PR shifts the behaviour change to the `Assert(Overflow*)` MIR terminators: if the crate is compiled without overflow checks, just skip emitting the assertions. This is already what happens with `OverflowNeg`.

This allows ConstProp and DataflowConstProp to transform `CheckedBinaryOp(Add, u8::MAX, 1)` into `const (0, true)`, and let codegen ignore the `true`.

 The interpreter is modified to conform to this behaviour.

Fixes #35310

1 files changed, 14 insertions, 0 deletions

diff --git a/tests/codegen/inherit_overflow.rs b/tests/codegen/inherit_overflow.rs
new file mode 100644
index 00000000000..0b0b890b2c9
--- /dev/null
+++ b/tests/codegen/inherit_overflow.rs
@@ -0,0 +1,14 @@
+// compile-flags: -Zmir-enable-passes=+Inline,+ConstProp --crate-type lib
+// revisions: ASSERT NOASSERT
+//[ASSERT] compile-flags: -Coverflow-checks=on
+//[NOASSERT] compile-flags: -Coverflow-checks=off
+
+// CHECK-LABEL: define{{.*}} @assertion
+// ASSERT: call void @_ZN4core9panicking5panic17h
+// NOASSERT: ret i8 0
+#[no_mangle]
+pub fn assertion() -> u8 {
+    // Optimized MIR will replace this `CheckedBinaryOp` by `const (0, true)`.
+    // Verify that codegen does or does not emit the panic.
+    <u8 as std::ops::Add>::add(255, 1)
+}