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

Author: bors

src/machine.rs

@@ -815,8 +815,8 @@ impl<'mir, 'tcx> Machine<'mir, 'tcx> for MiriMachine<'mir, 'tcx> {
     }
 
     #[inline(always)]
-    fn checked_binop_checks_overflow(ecx: &MiriInterpCx<'mir, 'tcx>) -> bool {
-        ecx.tcx.sess.overflow_checks()
+    fn ignore_checkable_overflow_assertions(ecx: &MiriInterpCx<'mir, 'tcx>) -> bool {
+        !ecx.tcx.sess.overflow_checks()
     }
 
     #[inline(always)]