compiler: interface typecodes are not passed through defer frames

[asdine]

I encountered a really weird compilation error, I tried to simplify the code to find the root cause and this is the best I could do:

package main

func main() {
	foo(nil)
}

type Bar struct {
	empty bool
}

func (b *Bar) Close() error {
	return nil
}

type Closer interface {
	Close() error
}

func foo(bar *Bar) error {
	var a int
	// replacing this condition with something simpler (i.e. nb > 10)
	// works fine
	if !bar.empty {
		a = 10
		// this inner branching is important
		if a != 5 {
			return nil
		}
	}

	var c Closer = bar
	// calling defer on an interface method + the branching above causes the bug
	// Replacing this line by func() { b.Close() }() works though
	defer c.Close()

	return nil
}

This causes the following compilation error:

Instruction does not dominate all uses!
  %3 = insertvalue %runtime._interface { i32 ptrtoint (%runtime.typeInInterface* @"typeInInterface:reflect/types.type:pointer:named:exp.Bar" to i32), i8* undef }, i8* %pack.ptr, 1
  %invoke.typecode16 = extractvalue %runtime._interface %3, 0
Instruction does not dominate all uses!
  %3 = insertvalue %runtime._interface { i32 ptrtoint (%runtime.typeInInterface* @"typeInInterface:reflect/types.type:pointer:named:exp.Bar" to i32), i8* undef }, i8* %pack.ptr, 1
  %invoke.func.receiver19 = extractvalue %runtime._interface %3, 1
error: verification error after IR construction

I compiled to wasm using the 0.12.0 docker image with the following params:

docker run ... \
    tinygo/tinygo:0.12.0 tinygo build -o /dist/exp.wasm -target wasm --no-debug exp

[niaow]

So, it appears that the IR generation for defer is attempting to extract the interface type directly from the source, rather than passing it through the defer frame. This can also be problematic if the defer is in a loop, in which case it could be tricked into interpreting with the wrong type.

[niaow]

v0.13 is getting close to release, so the fix is probably going to have to be pushed back into the next release window.

[niaow]

The bug fix was merged and will be included in the next release (v0.13).