[DependenceInfo] Track may-writes and build flow information in Dependences::calculateDependences.

[bollu]

Summary

This ensures that we handle may-writes correctly when building
dependence information. Also add a test case checking correctness of
may-write information. Not handling it before was an oversight.

[grosser]

LGTM.

polly/trunk/lib/Analysis/DependenceInfo.cpp

for (MemoryAccess *MA : Stmt) {
                  "handling.");
           isl_map *Schedule = tag(StmtScheduleMap, MA, Level);
           StmtSchedule = isl_union_map_add_map(StmtSchedule, Schedule);
         }
       }
 
       if (MA->isRead())
         Read = isl_union_map_add_map(Read, accdom);
+      else if (MA->isMayWrite())
+        MayWrite = isl_union_map_add_map(MayWrite, accdom);
       else
         Write = isl_union_map_add_map(Write, accdom);
     }
 
     if (!ReductionArrays.empty() && Level == Dependences::AL_Statement)
       StmtSchedule = isl_union_map_add_map(StmtSchedule, Stmt.getSchedule());
   }
 
DEBUG(dbgs() << "Read: " << Read << "\n";
     RAW = WAW = WAR = RED = nullptr;
 
     if (OptAnalysisType == VALUE_BASED_ANALYSIS) {
       isl_union_flow *Flow;
 
       Flow = buildFlow(Read, Write, MayWrite, Schedule);
 
       RAW = isl_union_flow_get_must_dependence(Flow);
+      RAW = isl_union_map_union(RAW, isl_union_flow_get_may_dependence(Flow));
       isl_union_flow_free(Flow);
 
       Flow = buildFlow(Write, Write, Read, Schedule);
 
       WAW = isl_union_flow_get_must_dependence(Flow);
       WAR = isl_union_flow_get_may_dependence(Flow);
 
       // This subtraction is needed to obtain the same results as were given by

polly/trunk/test/DependenceInfo/generate_may_write_dependence_info.ll

+; RUN: opt -S %loadPolly -polly-dependences -analyze < %s | FileCheck %s -check-prefix=VALUE
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+
+;                     for (int i = 0; i < N; i++) {
+; A.must.write.20:      A[i] = 20;
+;
+; compute.i.square:    if (i * i)
+; A.may.write.90:         A[i] = 90;
+;
+; B.write.from.A:       B[i] = A[i];
+; A.must.write.42:      A[i] = 42;
+;                     }
+define void @f(i32* %A, i32* %B) {
+entry:
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.inc, %entry
+  %indvars.iv = phi i64 [ %indvars.iv.next, %for.inc ], [ 0, %entry ]
+  %exitcond = icmp ne i64 %indvars.iv, 3000
+  br i1 %exitcond, label %A.must.write.20, label %for.end
+
+A.must.write.20:
+  %arrayidx = getelementptr inbounds i32, i32* %A, i64 %indvars.iv
+  store i32 20, i32* %arrayidx, align 4
+  br label %compute.i.square
+
+compute.i.square:
+  %tmp = mul nsw i64 %indvars.iv, %indvars.iv
+  %tmp2 = trunc i64 %tmp to i32
+  %tobool = icmp eq i32 %tmp2, 0
+  br i1 %tobool, label %B.write.from.A, label %A.may.write.90
+
+A.may.write.90:
+  %arrayidx2 = getelementptr inbounds i32, i32* %A, i64 %indvars.iv
+  store i32 90, i32* %arrayidx2, align 4
+  br label %B.write.from.A
+
+B.write.from.A:
+  %arrayidx4 = getelementptr inbounds i32, i32* %A, i64 %indvars.iv
+  %tmp3 = load i32, i32* %arrayidx4, align 4
+  %arrayidx6 = getelementptr inbounds i32, i32* %B, i64 %indvars.iv
+  store i32 %tmp3, i32* %arrayidx6, align 4
+  br label %A.must.write.42
+  ; br label %for.inc
+
+A.must.write.42:
+  %arrayidx5 = getelementptr inbounds i32, i32* %A, i64 %indvars.iv
+  store i32 42, i32* %arrayidx5, align 4
+  br label %for.inc
+
+for.inc:                                          ; preds = %if.end
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  br label %for.cond
+
+for.end:                                          ; preds = %for.cond
+  ret void
+}
+; VALUE: RAW dependences:
+; VALUE-NEXT:   { Stmt_A_must_write_20[i0] -> Stmt_B_write_from_A[i0] : 0 <= i0 <= 2999; Stmt_compute_i_square__TO__B_write_from_A[i0] -> Stmt_B_write_from_A[i0] : 0 <= i0 <= 2999 }
+; VALUE-NEXT: WAR dependences:
+; VALUE-NEXT:   { Stmt_A_must_write_20[i0] -> Stmt_A_must_write_42[i0] : 0 <= i0 <= 2999; Stmt_B_write_from_A[i0] -> Stmt_A_must_write_42[i0] : 0 <= i0 <= 2999 }
+; VALUE-NEXT: WAW dependences:
+; VALUE-NEXT:   {  }
+; VALUE-NEXT: Reduction dependences:
+; VALUE-NEXT:   {  }
+; VALUE-NEXT: Transitive closure of reduction dependences:
+; VALUE-NEXT:   {  }
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