Diff the LLVM-IR between two Git commits of a Rust crate

git-llvm-diff

#!/usr/bin/env bash
set -e

if [ "$#" -ne 2 ]; then
    echo "Usage: $0 <commit_A> <commit_B>"
    exit 1
fi

COMMIT_A=$1
COMMIT_B=$2
RUST_COMMIT_HASH=$(rustc --version --verbose | sed '3q;d' | cut -d' ' -f2)

echo "Comparing LLVM-IR between $COMMIT_A..$COMMIT_B"
echo "Rust toolchain commit hash: $RUST_COMMIT_HASH"

mkdir -p /tmp/git-llvm-diff
TREE_A="/tmp/git-llvm-diff/${RUST_COMMIT_HASH}_${COMMIT_A}"
TREE_B="/tmp/git-llvm-diff/${RUST_COMMIT_HASH}_${COMMIT_B}"

if [ ! -d "$TREE_A" ]; then
    mkdir "$TREE_A"
    git archive "$COMMIT_A" | tar -x -C "$TREE_A"
fi

if [ ! -d "$TREE_B" ]; then
    mkdir "$TREE_B"
    git archive "$COMMIT_B" | tar -x -C "$TREE_B"
fi

get_ll_mapping() {
    local tree=$1
    cd "$tree"
    RUSTFLAGS="-C lto=off --emit=llvm-ir --emit=asm -Z location-detail=none" cargo build --release --all-targets --benches --message-format=json | jq -r 'select(.reason == "compiler-artifact" and .executable != null) | "\(.target.name)\t\(.executable).ll"'
}

echo "Building COMMIT_A..."
declare -A LL_FILES_A
while IFS=$'\t' read -r target_name ll_path; do
    LL_FILES_A["$target_name"]="$ll_path"
done < <(get_ll_mapping "$TREE_A")

echo "Building COMMIT_B..."
declare -A LL_FILES_B
while IFS=$'\t' read -r target_name ll_path; do
    LL_FILES_B["$target_name"]="$ll_path"
done < <(get_ll_mapping "$TREE_B")

echo "Diffing LLVM-IR..."
for target in "${!LL_FILES_A[@]}"; do
    file_a="${LL_FILES_A[$target]}"
    file_b="${LL_FILES_B[$target]}"

    if [ -n "$file_b" ]; then
        printf "\033[1;34m========== llvm-diff: $target: ==========\033[0m\n"

        if [ -f "$file_a" ] && [ -f "$file_b" ]; then
            llvm-diff "$file_a" "$file_b" 2>&1 || true
        else
            echo "Warning: .ll file missing for $target"
            echo "Checked: $file_a"
            echo "     and $file_b"
        fi
        echo ""
    else
        echo "Target '$target' exists in Commit A but not in Commit B."
    fi
done