Auto merge of #142531 - ohadravid:better-storage-calls-copy-prop, r=tmiasko,cjgillot,saethlin

Remove fewer Storage calls in CopyProp and GVN



Modify the CopyProp and GVN MIR optimization passes to remove fewer `Storage{Live,Dead}` calls, allowing for better optimizations by LLVM - see rust-lang/rust#141649.

### Details

The idea is to use a new `MaybeUninitializedLocals` analysis and remove only the storage calls of locals that are maybe-uninit when accessed in a new location.

tests/codegen-llvm/issues/issue-141649.rs

@@ -0,0 +1,45 @@
+//@ compile-flags: -Copt-level=3
+
+#![crate_type = "lib"]
+
+// Non-overlapping scopes should produce correct llvm.lifetimes,
+// which allow reuse of the same stack allocation.
+
+pub struct WithOffset<T> {
+    pub data: T,
+    pub offset: usize,
+}
+
+#[inline(never)]
+pub fn peak_w(w: &WithOffset<&[u8; 16]>) {
+    std::hint::black_box(w);
+}
+
+#[inline(never)]
+pub fn use_w(w: WithOffset<&[u8; 16]>) {
+    std::hint::black_box(w);
+}
+
+// CHECK-LABEL: @scoped_small_structs
+// CHECK-NEXT: start:
+// CHECK-NEXT: [[B:%.*]] = alloca
+// CHECK-NEXT: [[A:%.*]] = alloca
+// CHECK: call void @llvm.lifetime.start.p0({{(i64 16, )?}}ptr {{.*}}[[A]])
+// CHECK: call void @llvm.lifetime.end.p0({{(i64 16, )?}}ptr {{.*}}[[A]])
+// CHECK: call void @llvm.lifetime.start.p0({{(i64 16, )?}}ptr {{.*}}[[B]])
+// CHECK: call void @llvm.lifetime.end.p0({{(i64 16, )?}}ptr {{.*}}[[B]])
+#[no_mangle]
+pub fn scoped_small_structs(buf: [u8; 16]) {
+    {
+        let w = WithOffset { data: &buf, offset: 0 };
+
+        peak_w(&w);
+        use_w(w);
+    }
+    {
+        let w2 = WithOffset { data: &buf, offset: 1 };
+
+        peak_w(&w2);
+        use_w(w2);
+    }
+}