ScopDetect: Transitively remove all children after region expansion

In rare cases, a region R which is itself not valid has an indirect child region
that is valid. When R becomes part of a valid region by expansion of another
region, then all children of R have to be erased from the set of valid regions.
This patch ensures that indirect children are erased in addition to direct
children.

Contributed-by: Armin Groesslinger <armin.groesslinger@uni-passau.de>

Tobias: I added a reduced test case and adjusted the logic of the patch to
        only recurse until the first child is found.
llvm-svn: 200411

polly/lib/Analysis/ScopDetection.cpp

@@ -590,6 +590,24 @@ static bool regionWithoutLoops(Region &R, LoopInfo *LI) {
   return true;
 }
 
+// Remove all direct and indirect children of region R from the region set Regs,
+// but do not recurse further if the first child has been found.
+//
+// Return the number of regions erased from Regs.
+static unsigned eraseAllChildren(std::set<const Region *> &Regs,
+                                 const Region *R) {
+  unsigned Count = 0;
+  for (Region::const_iterator I = R->begin(), E = R->end(); I != E; ++I) {
+    if (Regs.find(*I) != Regs.end()) {
+      ++Count;
+      Regs.erase(*I);
+    } else {
+      Count += eraseAllChildren(Regs, *I);
+    }
+  }
+  return Count;
+}
+
 void ScopDetection::findScops(Region &R) {
 
   if (!DetectRegionsWithoutLoops && regionWithoutLoops(R, LI))
@@ -640,9 +658,9 @@ void ScopDetection::findScops(Region &R) {
     ValidRegions.insert(ExpandedR);
     ValidRegions.erase(CurrentRegion);
 
-    for (Region::iterator I = ExpandedR->begin(), E = ExpandedR->end(); I != E;
+    // Erase all (direct and indirect) children of ExpandedR from the valid
-         ++I)
+    // regions and update the number of valid regions.
-      ValidRegions.erase(*I);
+    ValidRegion -= eraseAllChildren(ValidRegions, ExpandedR);
   }
 }
 

polly/test/ScopDetect/remove_all_children.ll

@@ -0,0 +1,46 @@
+; RUN: opt %loadPolly -polly-detect -analyze < %s | FileCheck %s
+; RUN: opt %loadPolly -polly-detect -polly-codegen-scev -analyze < %s | FileCheck %s
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @remove_all_children(i32* %eclass) {
+entry:
+  br label %while.body
+
+while.cond.loopexit:                              ; preds = %while.body50, %while.end44
+  fence seq_cst
+  br label %while.cond.backedge
+
+while.body:                                       ; preds = %while.cond.backedge, %entry
+  br label %if.end33
+
+while.cond.backedge:                              ; preds = %while.end30, %while.cond.loopexit
+  br i1 false, label %while.body, label %while.end60
+
+if.end33:                                         ; preds = %while.end30
+  br i1 false, label %while.body36, label %while.end44
+
+while.body36:                                     ; preds = %while.body36, %while.body36.lr.ph
+  %indvar77 = phi i64 [ 0, %if.end33 ], [ %indvar.next78, %while.body36 ]
+  %arrayidx40 = getelementptr i32* %eclass, i64 0
+  %indvar.next78 = add i64 %indvar77, 1
+  br i1 false, label %while.body36, label %while.end44
+
+while.end44:                                      ; preds = %while.body36, %if.end33
+  br i1 false, label %while.body50, label %while.cond.loopexit
+
+while.body50:                                     ; preds = %while.body50, %while.body50.lr.ph
+  %indvar79 = phi i64 [ 0, %while.end44 ], [ %indvar.next80, %while.body50 ]
+  %arrayidx55 = getelementptr i32* %eclass, i64 0
+  store i32 0, i32* %arrayidx55, align 4
+  %indvar.next80 = add i64 %indvar79, 1
+  br i1 false, label %while.body50, label %while.cond.loopexit
+
+while.end60:                                      ; preds = %while.cond.backedge
+  ret void
+}
+; remove_all_children
+; CHECK-NOT: Valid Region
+; CHECK: Valid Region for Scop: if.end33 => while.cond.loopexit
+; CHECK-NOT: Valid Region