fuzzgen: Add scalar float support (#4467)

* fuzzgen: Add float support

Add support for generating floats and some float instructions.

* fuzzgen: Enable NaN Canonicalization

Both IEEE754 and the Wasm spec are somewhat loose about what is allowed
to be returned from NaN producing operations. And in practice this changes
from X86 to Aarch64 and others. Even in the same host machine, the
interpreter may produce a code sequence different from cranelift that
generates different NaN's but produces legal results according to the spec.

These differences cause spurious failures in the fuzzer. To fix this
we enable the NaN Canonicalization pass that replaces any NaN's produced
with a single fixed canonical NaN value.

* fuzzgen: Use `MultiAry` when inserting opcodes

This deduplicates a few inserters!

cranelift/fuzzgen/src/lib.rs

@@ -5,7 +5,9 @@ use arbitrary::{Arbitrary, Unstructured};
 use cranelift::codegen::data_value::DataValue;
 use cranelift::codegen::ir::types::*;
 use cranelift::codegen::ir::Function;
+use cranelift::codegen::Context;
 use cranelift::prelude::*;
+use cranelift_native::builder_with_options;
 
 mod config;
 mod function_generator;
@@ -60,6 +62,10 @@ where
                 DataValue::from_integer(imm, ty)?
             }
             ty if ty.is_bool() => DataValue::B(bool::arbitrary(self.u)?),
+            // f{32,64}::arbitrary does not generate a bunch of important values
+            // such as Signaling NaN's / NaN's with payload, so generate floats from integers.
+            F32 => DataValue::F32(Ieee32::with_bits(u32::arbitrary(self.u)?)),
+            F64 => DataValue::F64(Ieee64::with_bits(u64::arbitrary(self.u)?)),
             _ => unimplemented!(),
         })
     }
@@ -81,10 +87,42 @@ where
         Ok(inputs)
     }
 
+    fn run_func_passes(&self, func: Function) -> Result<Function> {
+        // Do a NaN Canonicalization pass on the generated function.
+        //
+        // Both IEEE754 and the Wasm spec are somewhat loose about what is allowed
+        // to be returned from NaN producing operations. And in practice this changes
+        // from X86 to Aarch64 and others. Even in the same host machine, the
+        // interpreter may produce a code sequence different from cranelift that
+        // generates different NaN's but produces legal results according to the spec.
+        //
+        // These differences cause spurious failures in the fuzzer. To fix this
+        // we enable the NaN Canonicalization pass that replaces any NaN's produced
+        // with a single fixed canonical NaN value.
+        //
+        // This is something that we can enable via flags for the compiled version, however
+        // the interpreter won't get that version, so call that pass manually here.
+
+        let mut ctx = Context::for_function(func);
+        // Assume that we are generating this function for the current ISA
+        // this is only used for the verifier after `canonicalize_nans` so
+        // it's not too important.
+        let flags = settings::Flags::new(settings::builder());
+        let isa = builder_with_options(false)
+            .expect("Unable to build a TargetIsa for the current host")
+            .finish(flags)?;
+
+        ctx.canonicalize_nans(isa.as_ref())?;
+
+        Ok(ctx.func)
+    }
+
     pub fn generate_test(mut self) -> Result<TestCase> {
         let func = FunctionGenerator::new(&mut self.u, &self.config).generate()?;
         let inputs = self.generate_test_inputs(&func.signature)?;
 
+        let func = self.run_func_passes(func)?;
+
         Ok(TestCase { func, inputs })
     }
 }