Cranelift: hit unreachable case while lowering fcvt_to_uint

[elliottt]

.clif Test Case

function %f13(f32x4) -> i32x4 {                                                      
block0(v0: f32x4):                                                                   
  v1 = fcvt_to_uint.i32x4 v0                                                         
  return v1                                                                          
} 

Steps to Reproduce

Compiling this causes an unreachable case to be reached:

wasmtime/cranelift/codegen/src/isa/x64/lower.rs

Lines 800 to 804 in 380db48

	// Since this branch is also guarded by a check for vector types
	// neither Opcode::FcvtToUint nor Opcode::FcvtToSint can reach here
	// due to vector varients not existing. The first two branches will
	// cover all reachable cases.
	unreachable!();

Expected Results

Either an error or a successful compilation.

Actual Results

Panic

Versions and Environment

Cranelift version or commit: 0c2e049

Operating system: linux

Architecture: x86_64

[jlb6740]

Hi @elliottt . Does this unreachable case get hit before patch #4684 ?
I have not tried, but the comments here say this unreachable is guarded by both the Opcode::FcvtToUnit and Opcode::FcvtToSint. It looks like 4864 removed one of those branches and if so I wondering if that patch (removing that code) introduced the possibility of this fall through?

[elliottt]

I hit the panic at c4fd6a9, which is the direct parent of #4684. This panic is from fcvt_to_uint, vs fcvt_from_uint which was ported to ISLE in #4684.