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Auto merge of #124255 - RenjiSann:renji/mcdc-nested-expressions, r=Zalathar

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MCDC coverage: support nested decision coverage

#123409 provided the initial MCDC coverage implementation.

As referenced in #124144, it does not currently support "nested" decisions, like the following example :

```rust
fn nested_if_in_condition(a: bool, b: bool, c: bool) {
    if a && if b || c { true } else { false } {
        say("yes");
    } else {
        say("no");
    }
}
```

Note that there is an if-expression (`if b || c ...`) embedded inside a boolean expression in the decision of an outer if-expression.

This PR proposes a workaround for this cases, by introducing a Decision context stack, and by handing several `temporary condition bitmaps` instead of just one.
When instrumenting boolean expressions, if the current node is a leaf condition (i.e. not a `||`/`&&` logical operator nor a `!` not operator), we insert a new decision context, such that if there are more boolean expressions inside the condition, they are handled as separate expressions.

On the codegen LLVM side, we allocate as many `temp_cond_bitmap`s as necessary to handle the maximum encountered decision depth.
This commit is contained in:
bors 2024-04-29 11:54:49 +00:00
commit 7a58674259
12 changed files with 699 additions and 70 deletions
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31
compiler/rustc_codegen_llvm/src/builder.rs
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@ -27,6 +27,7 @@ use rustc_target::abi::{self, call::FnAbi, Align, Size, WrappingRange};
use rustc_target::spec::{HasTargetSpec, SanitizerSet, Target};
use smallvec::SmallVec;
use std::borrow::Cow;
use std::ffi::CString;
use std::iter;
use std::ops::Deref;
use std::ptr;
@ -1709,7 +1710,8 @@ impl<'a, 'll, 'tcx> Builder<'a, 'll, 'tcx> {
fn_name: &'ll Value,
hash: &'ll Value,
bitmap_bytes: &'ll Value,
) -> &'ll Value {
max_decision_depth: u32,
) -> Vec<&'ll Value> {
debug!("mcdc_parameters() with args ({:?}, {:?}, {:?})", fn_name, hash, bitmap_bytes);
assert!(llvm_util::get_version() >= (18, 0, 0), "MCDC intrinsics require LLVM 18 or later");
@ -1722,6 +1724,8 @@ impl<'a, 'll, 'tcx> Builder<'a, 'll, 'tcx> {
let args = &[fn_name, hash, bitmap_bytes];
let args = self.check_call("call", llty, llfn, args);
let mut cond_bitmaps = vec![];
unsafe {
let _ = llvm::LLVMRustBuildCall(
self.llbuilder,
@ -1733,17 +1737,22 @@ impl<'a, 'll, 'tcx> Builder<'a, 'll, 'tcx> {
0 as c_uint,
);
// Create condition bitmap named `mcdc.addr`.
let mut bx = Builder::with_cx(self.cx);
bx.position_at_start(llvm::LLVMGetFirstBasicBlock(self.llfn()));
let cond_bitmap = {
let alloca =
llvm::LLVMBuildAlloca(bx.llbuilder, bx.cx.type_i32(), c"mcdc.addr".as_ptr());
llvm::LLVMSetAlignment(alloca, 4);
alloca
};
bx.store(self.const_i32(0), cond_bitmap, self.tcx().data_layout.i32_align.abi);
cond_bitmap
for i in 0..=max_decision_depth {
let mut bx = Builder::with_cx(self.cx);
bx.position_at_start(llvm::LLVMGetFirstBasicBlock(self.llfn()));
let name = CString::new(format!("mcdc.addr.{i}")).unwrap();
let cond_bitmap = {
let alloca =
llvm::LLVMBuildAlloca(bx.llbuilder, bx.cx.type_i32(), name.as_ptr());
llvm::LLVMSetAlignment(alloca, 4);
alloca
};
bx.store(self.const_i32(0), cond_bitmap, self.tcx().data_layout.i32_align.abi);
cond_bitmaps.push(cond_bitmap);
}
}
cond_bitmaps
}
pub(crate) fn mcdc_tvbitmap_update(