This test case is triggered in a couple of LNT failures I see.

I am not sure how we can compute something more efficiently here, sorry. The example test case simply has up to 2^10 many paths from the region entry to the exit, thus it is not suprising it takes a while to describe them all.

I would suggest to bail out, maybe if the number of parameters is too high or maybe if there are to many conditional branches in the same loop.

Test case
With the following patch and the attached test case I get a very simple set of conditions (precisely the ones I expect):

--- a/lib/Analysis/ScopInfo.cpp
+++ b/lib/Analysis/ScopInfo.cpp
@@ -1930,7 +1930,6 @@ void Scop::buildDomainsWithBranchConstraints(Region *R) {
// executed at runtime.
if (containsErrorBlock(RN, getRegion(), LI, DT)) {
HasErrorBlock = true;

•  continue;
  

  }

  BasicBlock *BB = getRegionNodeBasicBlock(RN);

    Stmt_bb15
        Domain :=
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb15[] };
        Schedule :=
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb15[] -> [0] };
        MustWriteAccess :=	[Reduction Type: NONE] [Scalar: 0]
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb15[] -> MemRef_A[0] };
    Stmt_bb19
        Domain :=
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb19[] : tmp17 <= -1 or tmp17 >= 1 };
        Schedule :=
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb19[] -> [1] : tmp17 <= -1 or tmp17 >= 1 };
        MustWriteAccess :=	[Reduction Type: NONE] [Scalar: 0]
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb19[] -> MemRef_A[0] };
    Stmt_bb24
        Domain :=
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb24[] };
        Schedule :=
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb24[] -> [2] };
        MustWriteAccess :=	[Reduction Type: NONE] [Scalar: 0]
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb24[] -> MemRef_A[0] };
    Stmt_bb29
        Domain :=
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb29[] : tmp27 = 3 };
        Schedule :=
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb29[] -> [3] };
        MustWriteAccess :=	[Reduction Type: NONE] [Scalar: 0]
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb29[] -> MemRef_A[0] };
    Stmt_bb34
        Domain :=
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb34[] };
        Schedule :=
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb34[] -> [4] };
        MustWriteAccess :=	[Reduction Type: NONE] [Scalar: 0]
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb34[] -> MemRef_A[0] };
    Stmt_bb39
        Domain :=
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb39[] : tmp37 <= -1 or tmp37 >= 1 };
        Schedule :=
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb39[] -> [5] : tmp37 <= -1 or tmp37 >= 1 };
        MustWriteAccess :=	[Reduction Type: NONE] [Scalar: 0]
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb39[] -> MemRef_A[0] };
    Stmt_bb43
        Domain :=
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb43[] : (tmp37 <= -1 and tmp41 <= -1) or (tmp37 <= -1 and tmp41 >= 1) or (tmp37 >= 1 and tmp41 <= -1) or (tmp37 >= 1 and tmp41 >= 1) };
        Schedule :=
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb43[] -> [6] : (tmp37 <= -1 and tmp41 <= -1) or (tmp37 <= -1 and tmp41 >= 1) or (tmp37 >= 1 and tmp41 <= -1) or (tmp37 >= 1 and tmp41 >= 1) };
        MustWriteAccess :=	[Reduction Type: NONE] [Scalar: 0]
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb43[] -> MemRef_A[0] };
    Stmt_bb49
        Domain :=
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb49[] };
        Schedule :=
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb49[] -> [7] };
        MustWriteAccess :=	[Reduction Type: NONE] [Scalar: 0]
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb49[] -> MemRef_A[0] };
    Stmt_bb54
        Domain :=
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb54[] : tmp52 <= -1 or tmp52 >= 1 };
        Schedule :=
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb54[] -> [8] : tmp52 <= -1 or tmp52 >= 1 };
        MustWriteAccess :=	[Reduction Type: NONE] [Scalar: 0]
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb54[] -> MemRef_A[0] };
    Stmt_bb59
        Domain :=
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb59[] : tmp52 <= -1 or tmp52 >= 0 };
        Schedule :=
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb59[] -> [9] };
        MustWriteAccess :=	[Reduction Type: NONE] [Scalar: 0]
            [tmp17, tmp21, tmp27, tmp31, tmp37, tmp41, tmp46, tmp52, tmp56, tmp62] -> { Stmt_bb59[] -> MemRef_A[0] };
  

So the issue is that isl_set_coalesce() does not work due to us bailing out at error blocks. I think either we should not bail out for error blocks or we should try to propagate conditions forward from earlier basic blocks. Maybe the ones that dominate the block we look at, that are at themselves postdominated by the block we look at and that are at the same loop depth as the basic block we look at.

This test case also computes a rather complex assumed context (even after me commenting out the continue). My feeling is this assumed context could also be described with simpler sets.

This has been addressed in r252750.

Move to Polly Product.