[Simplify] Count PHINodes in simplifiable exit nodes as escaping use.

After region exit simplification, the incoming block of a phi node in
the SCoP region's exit block lands outside of the region. Since we
treat SCoPs as if this already happened, we need to account for that
when looking for outside uses of scalars (i.e. escaping scalars).

llvm-svn: 309271

polly/lib/Support/VirtualInstruction.cpp

@@ -170,6 +170,13 @@ static bool isEscaping(Scop *S, Instruction *ComputingInst) {
     BasicBlock *UserBB = getUseBlock(Use);
     if (!S->contains(UserBB))
       return true;
+
+    // When the SCoP region exit needs to be simplified, PHIs in the region exit
+    // move to a new basic block such that its incoming blocks are not in the
+    // scop anymore.
+    if (S->hasSingleExitEdge() && isa<PHINode>(Use.getUser()) &&
+        S->isExit(cast<PHINode>(Use.getUser())->getParent()))
+      return true;
   }
   return false;
 }

polly/test/Simplify/exit_phi_accesses-2.ll

@@ -0,0 +1,37 @@
+; RUN: opt %loadPolly -polly-scops -polly-simplify -analyze < %s | FileCheck %s
+;
+; The use of %sum.next by %phi counts as an escaping use.
+; Don't remove the scalar write of %sum.next.
+;
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+define float @foo(float* %A) {
+entry:
+  br label %header
+
+header:
+  fence seq_cst
+  br i1 true, label %body, label %exit
+
+body:
+  %i = phi i64 [ 0, %header ], [ %next, %body ]
+  %sum = phi float [ 0.0, %header ], [ %sum.next, %body ]
+  %arrayidx = getelementptr float, float* %A, i64 %i
+  %next = add nuw nsw i64 %i, 1
+  %val = load float, float* %arrayidx
+  %sum.next = fadd float %sum, %val
+  %cond = icmp ne i64 %i, 100
+  br i1 %cond, label %body, label %after
+
+after:
+  br label %exit
+
+exit:
+  %phi = phi float [%sum.next, %after], [0.0, %header]
+  ret float %phi
+}
+
+
+; CHECK: Statistics {
+; CHECK:     Dead accesses removed: 0
+; CHECK: }