fix: copy a short return tail reached from a loop body and from before the loop - #3026

Description

fixes #2781 . the method from the issue decompiled to code that keeps looping after str = "pass" and returns false , where the real method logs and returns true .

the loop body jumps to log(...); return true; , and the same two instructions are also reached from the else branch before the loop . the loop's normal exit goes to return false , so a break can't reach that tail , and the jump was dropped . splitReturn would copy the return for each predecessor , but the return sits in its own block after the log call , so the block with two predecessors isn't the return block .

this adds splitLoopExitTail next to splitReturn : if a return is preceded by a short straight tail (up to 4 instructions) that is reached both from a loop body exit and from outside the loop , the tail is copied for the loop side . it only fires when the tail is not the loop's normal exit , so a compound loop condition or a plain break keeps its current output . the issue method now comes out as

if (string.equals("abc")) {
    log("TAG", "pass");
    return true;
}

the new smali test is the issue's method with the android types swapped for java.lang ones , and it fails without the change . jadx-core tests : 1034 passed , 0 failed .

i also decompiled a 20 MB apk (the sample from #2892) with and without the change . nothing changed apart from throws clauses that already differ between two runs of the unchanged build , MethodThrowsVisitor hits a ConcurrentModificationException there with -j 8 .

spotlessCheck could not fetch its eclipse formatter here , so the formatting is checked by hand against the file .