Add some more context to the CLIF verifier

Helps when debugging verifier failures.

Author: fitzgen

cranelift/codegen/src/ir/instructions.rs

@@ -807,7 +807,7 @@ impl OperandConstraint {
                     // control type to construct the interval of [F16, ctrl_type).
                     tys.floats = BitSet8::from_range(4, ctrl_type_bits as u8);
                 } else {
-                    panic!("The Narrower constraint only operates on floats or ints");
+                    panic!("The Narrower constraint only operates on floats or ints, got {ctrl_type:?}");
                 }
                 ResolvedConstraint::Free(tys)
             }
@@ -838,7 +838,9 @@ impl OperandConstraint {
                         tys.floats = BitSet8::from_range(lower_bound, 8);
                     }
                 } else {
-                    panic!("The Wider constraint only operates on floats or ints");
+                    panic!(
+                        "The Wider constraint only operates on floats or ints, got {ctrl_type:?}"
+                    );
                 }
 
                 ResolvedConstraint::Free(tys)

cranelift/codegen/src/verifier/mod.rs

@@ -1766,6 +1766,7 @@ impl<'a> Verifier<'a> {
                 return errors.fatal((block, format!("{block} cannot be empty")));
             }
             for inst in self.func.layout.block_insts(block) {
+                crate::trace!("verifying {inst:?}: {}", self.func.dfg.display_inst(inst));
                 self.block_integrity(block, inst, errors)?;
                 self.instruction_integrity(inst, errors)?;
                 self.typecheck(inst, errors)?;