[Polly][Acc] Fix for PR33208

[philip.pfaffe]

Summary

During codegen, Polly attempts to clear all loops from ScalarEvolution and LoopInfo, and it does so one block at a time. This causes undefined behaviour, since this way a loop header might be removed from a loop before the entire loop is erased, causing ScalarEvolution to run into an error.

Instead, just delete the entire loop atomically.

[grosser]

Cool. Any chance you could add a test case?

Tobias

[philip.pfaffe]

This is a fix for existing currently failing testcases, I think that should cover it.

[grosser]

OK. Maybe mention this in the commit message?

[philip.pfaffe]

It was in the PR, but I'll mention it in the commit.

[philip.pfaffe]

My bad, I uploaded the reverse diff ...

[philip.pfaffe]

Commited in rPLO326643, reverted in rPLO326656.

While this fix closed a couple of test failures, it just shifted a few others, which look like they have the same root cause.

polly/lib/CodeGen/PPCGCodeGeneration.cpp

void GPUNodeBuilder::clearDominators(Function *F) {
   for (po_iterator<DomTreeNode *> I = po_begin(N), E = po_end(N); I != E; ++I)
     Nodes.push_back(I->getBlock());
 
   for (BasicBlock *BB : Nodes)
     DT.eraseNode(BB);
 }
 
 void GPUNodeBuilder::clearScalarEvolution(Function *F) {
-  for (BasicBlock &BB : *F) {
-    Loop *L = LI.getLoopFor(&BB);
+  for (auto *L : LI)
     if (L)
       SE.forgetLoop(L);
-  }
-}
 
 void GPUNodeBuilder::clearLoops(Function *F) {
-  for (BasicBlock &BB : *F) {
-    Loop *L = LI.getLoopFor(&BB);
-    if (L)
-      SE.forgetLoop(L);
-    LI.removeBlock(&BB);
-  }
+  clearScalarEvolution(F);
+  SmallVector<Loop *, 1> Loops(LI.begin(), LI.end());
+  for (auto *L : Loops)
+    LI.erase(L);
 }
 
 std::tuple<Value *, Value *> GPUNodeBuilder::getGridSizes(ppcg_kernel *Kernel) {
   std::vector<Value *> Sizes;
   isl::ast_build Context = isl::ast_build::from_context(S.getContext());
 
   isl::multi_pw_aff GridSizePwAffs =
       isl::manage(isl_multi_pw_aff_copy(Kernel->grid_size));