[PATCH] D18450: Use RegionInfo as shortcut in part of the domain generation [WIP]

[Johannes Doerfert via llvm-commits]

jdoerfert created this revision.
jdoerfert added reviewers: grosser, Meinersbur, chrisj.
jdoerfert added a subscriber: Polly.

  As alternative to DomTree + PostDomTree we can use the RegionInfo to
  propagate domains. In particular we use the fact that the domain of
  the entry node of a region is a subset of the domain of the exit node
  of the same region. In case the exit node is only reached from this
  region, they have even the same domain. To this end we do not need to
  propagate domain information to the exit from within the region.

  This commit is marked [WIP] as it:
    1) depends on another patch that bails out of the domain generation
       as soon as a problem was detected (will be upstreamed)
    2) lacks a comment

  One might want to refactor the domain gen a little bit to make this
  even more powerful (e.g., lift the same loop restriction and use it in
  all parts of the domain generation).

http://reviews.llvm.org/D18450

Files:
  lib/Analysis/ScopInfo.cpp
  test/ScopInfo/remarks.ll

Index: test/ScopInfo/remarks.ll
===================================================================
--- test/ScopInfo/remarks.ll
+++ test/ScopInfo/remarks.ll
@@ -1,9 +1,9 @@
 ; RUN: opt %loadPolly -pass-remarks-analysis="polly-scops" -polly-scops -disable-output < %s 2>&1 | FileCheck %s
 ;
 ; CHECK: remark: test/ScopInfo/remarks.c:4:7: SCoP begins here.
-; CHECK: remark: test/ScopInfo/remarks.c:8:5: Finite loop restriction:    [M, N, Debug] -> {  : M < 0 and N > 0 }
+; CHECK: remark: test/ScopInfo/remarks.c:8:5: Finite loop restriction:    [M, N] -> {  : M < 0 and N > 0 }
 ; CHECK: remark: test/ScopInfo/remarks.c:13:7: No-error restriction:    [M, N, Debug] -> {  : M >= 0 and N > 0 and (Debug < 0 or Debug > 0) }
-; CHECK: remark: test/ScopInfo/remarks.c:9:7: Inbounds assumption:    [M, N, Debug] -> {  : M <= 100 or (M > 0 and N <= 0) }
+; CHECK: remark: test/ScopInfo/remarks.c:9:7: Inbounds assumption:    [M, N] -> {  : M <= 100 or (M > 0 and N <= 0) }
 ; CHECK: remark: <unknown>:0:0: No-overflows restriction:    [N, M, Debug] -> {  : M <= -2147483649 - N or M >= 2147483648 - N }
 ; CHECK: remark: test/ScopInfo/remarks.c:9:18: Possibly aliasing pointer, use restrict keyword.
 ; CHECK: remark: test/ScopInfo/remarks.c:9:33: Possibly aliasing pointer, use restrict keyword.
Index: lib/Analysis/ScopInfo.cpp
===================================================================
--- lib/Analysis/ScopInfo.cpp
+++ lib/Analysis/ScopInfo.cpp
@@ -2193,6 +2193,8 @@
   // As we are only interested in non-loop carried constraints here we can
   // simply skip loop back edges.
 
+  auto *RI = R->getRegionInfo();
+  SmallPtrSet<BasicBlock *, 8> FinishedExitBlocks;
   ReversePostOrderTraversal<Region *> RTraversal(R);
   for (auto *RN : RTraversal) {
 
@@ -2223,6 +2225,27 @@
     Loop *BBLoop = getRegionNodeLoop(RN, LI);
     int BBLoopDepth = getRelativeLoopDepth(BBLoop);
 
+    // Check if we can use the region info to determine the domain of some
+    // other block from the domain of this one.
+    auto *BBReg = RI ? RI->getRegionFor(BB) : nullptr;
+    if (BBReg && BBReg->getEntry() == BB) {
+      auto *ExitBB = BBReg->getExit();
+      if (BBLoop == LI.getLoopFor(ExitBB)) {
+        isl_set *&ExitDomain = DomainMap[ExitBB];
+        if (ExitDomain)
+          ExitDomain = isl_set_union(isl_set_copy(Domain), ExitDomain);
+        else
+          ExitDomain = isl_set_copy(Domain);
+        FinishedExitBlocks.insert(ExitBB);
+      }
+    }
+
+    if (std::all_of(succ_begin(BB), succ_end(BB),
+                    [&FinishedExitBlocks](BasicBlock *SuccBB) {
+                      return FinishedExitBlocks.count(SuccBB);
+                    }))
+      continue;
+
     // Build the condition sets for the successor nodes of the current region
     // node. If it is a non-affine subregion we will always execute the single
     // exit node, hence the single entry node domain is the condition set. For
@@ -2242,6 +2265,11 @@
       isl_set *CondSet = ConditionSets[u];
       BasicBlock *SuccBB = getRegionNodeSuccessor(RN, TI, u);
 
+      if (FinishedExitBlocks.count(SuccBB)) {
+        isl_set_free(CondSet);
+        continue;
+      }
+
       // Skip back edges.
       if (DT.dominates(SuccBB, BB)) {
         isl_set_free(CondSet);


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