Created attachment 127699 [details]
testcase

Reduced test case:

public class Stack<T> {
	public T peek () throws Error 	{
		return null;
	}
}

public static void main (string[] args) {
	Stack<string> st = new Stack<string> ();
	while (st.peek ()) {
	}
}

Created attachment 131517 [details] [review]
Patch

Moves conditional split farther up the analysis tree for loop conditions, preventing recursing into partially-completed analysis when conditional expressions can throw errors.

Thanks for the patch. Unfortunately, removing the code that handles method calls that can throw errors can lead to incorrect code. For example, if you assign the result of a method call to a local variable, the compiler will not catch the error until after the assignment if your patch is applied. However, the assignment must not happen in the error case.

Created attachment 132792 [details] [review]
Patch

Reworked patch.

Thanks for the updated patch. It still causes some regressions. For example, the following test case results in an endless loop with your patch applied:

public class Stack<T> {
	static int i = 0;
        public bool peek () throws Error   {
                return (i++ == 0);
        }
}

public static void main (string[] args) {
        Stack<string> st = new Stack<string> ();
        while (st.peek ()) {
        }
}

Created attachment 134563 [details] [review]
Patch

Reworked again per comments.

Thanks for the update. The patch goes into the right direction by doing the transformation earlier. To avoid similar issues in the future, I'll take the patch a step further and transform all while, do, and for loops into one simple loop type without a condition. This simplifies code in semantic and flow analysis and code generation.

commit fef10859ae29c524cac6a7388759f02e26df160d
Author: Jürg Billeter <j@bitron.ch>
Date:   Sat Jun 6 17:04:02 2009 +0200

    Convert for loops into simple loops

commit a71e6e0dea67455e741ffe319f796419a3fa42fe
Author: Jürg Billeter <j@bitron.ch>
Date:   Sat Jun 6 16:20:32 2009 +0200

    Convert do loops into simple loops

commit 14cb3893cf381f6b9136eccccdba86bc42786a56
Author: Jürg Billeter <j@bitron.ch>
Date:   Sat Jun 6 15:58:44 2009 +0200

    Convert while loops into simple loops
    
    Simplifies and fixes bugs in semantic and flow analysis and code
    generation. Based on patch by Levi Bard, fixes bug 570091.