[polly] r206318 - Dependences: Do not fail in case a schedule eliminates all dependences

[Tobias Grosser]

Author: grosser
Date: Tue Apr 15 15:14:57 2014
New Revision: 206318

URL: http://llvm.org/viewvc/llvm-project?rev=206318&view=rev
Log:
Dependences: Do not fail in case a schedule eliminates all dependences

The following example shows a non-parallel loop

void f(int a[]) {
  int i;
  for (i = 0; i < 10; ++i)
    A[i] = A[i+5];
}

which, in case we import a schedule that limits the iteration domain
to 0 <= i < 5, becomes parallel. Previously we crashed in such cases, now we
just recognize it as parallel.

This fixes http://llvm.org/PR19435

Reported-by: Jeremy Huddleston Sequoia <jeremyhu at apple.com>

Added:
    polly/trunk/test/Cloog/CodeGen/reduced-domain-eliminates-dependences.ll
    polly/trunk/test/Cloog/CodeGen/reduced-domain-eliminates-dependences___%bb---%return.jscop
Modified:
    polly/trunk/lib/Analysis/Dependences.cpp

Modified: polly/trunk/lib/Analysis/Dependences.cpp
URL: http://llvm.org/viewvc/llvm-project/polly/trunk/lib/Analysis/Dependences.cpp?rev=206318&r1=206317&r2=206318&view=diff
==============================================================================
--- polly/trunk/lib/Analysis/Dependences.cpp (original)
+++ polly/trunk/lib/Analysis/Dependences.cpp Tue Apr 15 15:14:57 2014
@@ -273,6 +273,13 @@ bool Dependences::isParallelDimension(__
   Schedule = getCombinedScheduleForSpace(S, ParallelDim);
   Deps = isl_union_map_apply_range(Deps, isl_union_map_copy(Schedule));
   Deps = isl_union_map_apply_domain(Deps, Schedule);
+
+  if (isl_union_map_is_empty(Deps)) {
+    isl_union_map_free(Deps);
+    isl_set_free(ScheduleSubset);
+    return true;
+  }
+
   ScheduleDeps = isl_map_from_union_map(Deps);
   ScheduleDeps =
       isl_map_intersect_domain(ScheduleDeps, isl_set_copy(ScheduleSubset));

Added: polly/trunk/test/Cloog/CodeGen/reduced-domain-eliminates-dependences.ll
URL: http://llvm.org/viewvc/llvm-project/polly/trunk/test/Cloog/CodeGen/reduced-domain-eliminates-dependences.ll?rev=206318&view=auto
==============================================================================
--- polly/trunk/test/Cloog/CodeGen/reduced-domain-eliminates-dependences.ll (added)
+++ polly/trunk/test/Cloog/CodeGen/reduced-domain-eliminates-dependences.ll Tue Apr 15 15:14:57 2014
@@ -0,0 +1,35 @@
+; RUN: opt %loadPolly -polly-import-jscop -polly-import-jscop-dir=%S -polly-codegen -polly-vectorizer=polly < %s
+
+; void f(int a[]) {
+;  int i;
+;  for (i = 0; i < 10; ++i)
+;    A[i] = A[i+5];
+; }
+
+; In this test case we import a schedule that limits the iteration domain
+; to 0 <= i < 5, which makes the loop parallel. Previously we crashed in such
+; cases. This test checks that we instead vectorize the loop.
+
+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"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @reduced-domain-eliminates-dependences(i64* %a) {
+entry:
+  br label %bb
+
+bb:
+  %indvar = phi i64 [ 0, %entry ], [ %indvar.next, %bb ]
+  %add = add i64 %indvar, 5
+  %scevgep.load = getelementptr i64* %a, i64 %add
+  %scevgep.store = getelementptr i64* %a, i64 %indvar
+  %val = load i64* %scevgep.load
+  store i64 %val, i64* %scevgep.store, align 8
+  %indvar.next = add nsw i64 %indvar, 1
+  %exitcond = icmp eq i64 %indvar.next, 10
+  br i1 %exitcond, label %return, label %bb
+
+return:
+  ret void
+}
+
+; CHECK: store <4 x i64> %val_p_vec_full, <4 x i64>* %vector_ptr10

Added: polly/trunk/test/Cloog/CodeGen/reduced-domain-eliminates-dependences___%bb---%return.jscop
URL: http://llvm.org/viewvc/llvm-project/polly/trunk/test/Cloog/CodeGen/reduced-domain-eliminates-dependences___%25bb---%25return.jscop?rev=206318&view=auto
==============================================================================
--- polly/trunk/test/Cloog/CodeGen/reduced-domain-eliminates-dependences___%bb---%return.jscop (added)
+++ polly/trunk/test/Cloog/CodeGen/reduced-domain-eliminates-dependences___%bb---%return.jscop Tue Apr 15 15:14:57 2014
@@ -0,0 +1,21 @@
+{
+   "context" : "{  :  }",
+   "name" : "bb => return",
+   "statements" : [
+      {
+         "accesses" : [
+            {
+               "kind" : "read",
+               "relation" : "{ Stmt_bb[i0] -> MemRef_a[5 + i0] }"
+            },
+            {
+               "kind" : "write",
+               "relation" : "{ Stmt_bb[i0] -> MemRef_a[i0] }"
+            }
+         ],
+         "domain" : "{ Stmt_bb[i0] : i0 >= 0 and i0 <= 10 }",
+         "name" : "Stmt_bb",
+         "schedule" : "{ Stmt_bb[i0] -> scattering[0, i0, 0]: i0 < 4 }"
+      }
+   ]
+}