Set LLVM Flag to Disable cmov (select instr) generation

src/options.rs

@@ -134,6 +134,13 @@ pub struct BuildOptions {
     /// the `*-trace-compares` instrumentation assumes that the instruction is
     /// available.
     pub no_trace_compares: bool,
+
+    #[arg(long)]
+    /// Disable transformation of if-statements into `cmov` instructions (when this
+    /// happens, we get no coverage feedback for that branch). Default setting is true.
+    /// A further explanation can be found here:
+    /// https://github.com/rust-fuzz/cargo-fuzz/pull/380#issue-2445529059
+    pub disable_branch_folding: Option<bool>,
 }
 
 impl stdfmt::Display for BuildOptions {
@@ -233,6 +240,7 @@ mod test {
             strip_dead_code: false,
             no_cfg_fuzzing: false,
             no_trace_compares: false,
+            disable_branch_folding: None,
         };
 
         let opts = vec![

src/project.rs

@@ -175,6 +175,10 @@ impl FuzzProject {
             rustflags.push_str(" -Cllvm-args=-sanitizer-coverage-trace-compares");
         }
 
+        if build.disable_branch_folding.unwrap_or(true) {
+            rustflags.push_str(" -Cllvm-args=-simplifycfg-branch-fold-threshold=0");
+        }
+
         if !build.no_cfg_fuzzing {
             rustflags.push_str(" --cfg fuzzing");
         }