Auto merge of #108872 - cjgillot:simp-const-prop, r=oli-obk

Strengthen state tracking in const-prop

Some/many of the changes are replicated between both the const-prop lint and the const-prop optimization.

Behaviour changes:
- const-prop opt does not give a span to propagated values. This was useless as that span's primary purpose is to diagnose evaluation failure in codegen.
- we remove the `OnlyPropagateInto` mode. It was only used for function arguments, which are better modeled by a write before entry.
- the tracking of assignments and discriminants make clearer that we do nothing in `NoPropagation` mode or on indirect places.

tests/ui/erasing_op.rs

@@ -31,9 +31,7 @@ impl core::ops::Mul<i32> for Vec1 {
 
 #[allow(clippy::no_effect)]
 #[warn(clippy::erasing_op)]
-fn main() {
+fn test(x: u8) {
-    let x: u8 = 0;
-
     x * 0;
     0 & x;
     0 / x;
@@ -41,3 +39,7 @@ fn main() {
     0 * Vec1 { x: 5 };
     Vec1 { x: 5 } * 0;
 }
+
+fn main() {
+    test(0)
+}

tests/ui/erasing_op.stderr

@@ -1,5 +1,5 @@
 error: this operation will always return zero. This is likely not the intended outcome
-  --> $DIR/erasing_op.rs:37:5
+  --> $DIR/erasing_op.rs:35:5
    |
 LL |     x * 0;
    |     ^^^^^
@@ -7,25 +7,25 @@ LL |     x * 0;
    = note: `-D clippy::erasing-op` implied by `-D warnings`
 
 error: this operation will always return zero. This is likely not the intended outcome
-  --> $DIR/erasing_op.rs:38:5
+  --> $DIR/erasing_op.rs:36:5
    |
 LL |     0 & x;
    |     ^^^^^
 
 error: this operation will always return zero. This is likely not the intended outcome
-  --> $DIR/erasing_op.rs:39:5
+  --> $DIR/erasing_op.rs:37:5
    |
 LL |     0 / x;
    |     ^^^^^
 
 error: this operation will always return zero. This is likely not the intended outcome
-  --> $DIR/erasing_op.rs:41:5
+  --> $DIR/erasing_op.rs:39:5
    |
 LL |     0 * Vec1 { x: 5 };
    |     ^^^^^^^^^^^^^^^^^
 
 error: this operation will always return zero. This is likely not the intended outcome
-  --> $DIR/erasing_op.rs:42:5
+  --> $DIR/erasing_op.rs:40:5
    |
 LL |     Vec1 { x: 5 } * 0;
    |     ^^^^^^^^^^^^^^^^^

tests/ui/integer_arithmetic.rs

@@ -4,7 +4,7 @@
 #[rustfmt::skip]
 fn main() {
     let mut i = 1i32;
-    let mut var1 = 0i32;
+    let mut var1 = 13i32;
     let mut var2 = -1i32;
     1 + i;
     i * 2;

tests/ui/overflow_check_conditional.rs

@@ -1,9 +1,6 @@
 #![warn(clippy::overflow_check_conditional)]
 
-fn main() {
+fn test(a: u32, b: u32, c: u32) {
-    let a: u32 = 1;
-    let b: u32 = 2;
-    let c: u32 = 3;
     if a + b < a {}
     if a > a + b {}
     if a + b < b {}
@@ -23,3 +20,7 @@ fn main() {
     if i > i + j {}
     if i - j < i {}
 }
+
+fn main() {
+    test(1, 2, 3)
+}

tests/ui/overflow_check_conditional.stderr

@@ -1,5 +1,5 @@
 error: you are trying to use classic C overflow conditions that will fail in Rust
-  --> $DIR/overflow_check_conditional.rs:7:8
+  --> $DIR/overflow_check_conditional.rs:4:8
    |
 LL |     if a + b < a {}
    |        ^^^^^^^^^
@@ -7,43 +7,43 @@ LL |     if a + b < a {}
    = note: `-D clippy::overflow-check-conditional` implied by `-D warnings`
 
 error: you are trying to use classic C overflow conditions that will fail in Rust
-  --> $DIR/overflow_check_conditional.rs:8:8
+  --> $DIR/overflow_check_conditional.rs:5:8
    |
 LL |     if a > a + b {}
    |        ^^^^^^^^^
 
 error: you are trying to use classic C overflow conditions that will fail in Rust
-  --> $DIR/overflow_check_conditional.rs:9:8
+  --> $DIR/overflow_check_conditional.rs:6:8
    |
 LL |     if a + b < b {}
    |        ^^^^^^^^^
 
 error: you are trying to use classic C overflow conditions that will fail in Rust
-  --> $DIR/overflow_check_conditional.rs:10:8
+  --> $DIR/overflow_check_conditional.rs:7:8
    |
 LL |     if b > a + b {}
    |        ^^^^^^^^^
 
 error: you are trying to use classic C underflow conditions that will fail in Rust
-  --> $DIR/overflow_check_conditional.rs:11:8
+  --> $DIR/overflow_check_conditional.rs:8:8
    |
 LL |     if a - b > b {}
    |        ^^^^^^^^^
 
 error: you are trying to use classic C underflow conditions that will fail in Rust
-  --> $DIR/overflow_check_conditional.rs:12:8
+  --> $DIR/overflow_check_conditional.rs:9:8
    |
 LL |     if b < a - b {}
    |        ^^^^^^^^^
 
 error: you are trying to use classic C underflow conditions that will fail in Rust
-  --> $DIR/overflow_check_conditional.rs:13:8
+  --> $DIR/overflow_check_conditional.rs:10:8
    |
 LL |     if a - b > a {}
    |        ^^^^^^^^^
 
 error: you are trying to use classic C underflow conditions that will fail in Rust
-  --> $DIR/overflow_check_conditional.rs:14:8
+  --> $DIR/overflow_check_conditional.rs:11:8
    |
 LL |     if a < a - b {}
    |        ^^^^^^^^^