commit c96c1d8c87982f2341dba5fb31ee90ae41b31f4c
author Tobias Grosser <tobias@grosser.es> Thu Apr 27 20:08:16 2017 +0000
committer Tobias Grosser <tobias@grosser.es> Thu Apr 27 20:08:16 2017 +0000
tree dd4764730ce91d79d18c4fbc019837d04c531819
parent 9a98df63f436213d89f4b3df351fb7602c6597ea

[ScopInfo] Consider only write-free dereferencable loads as invariant

When we introduced in r297375 support for hoisting loads that are known
to be dereferencable without any conditional guard, we forgot to keep the check
to verify that no other write into the very same location exists. This
change ensures now that dereferencable loads are allowed to access everything,
but can only be hoisted in case no conflicting write exists.

This resolves llvm.org/PR32778

Reported-by: Huihui Zhang <huihuiz@codeaurora.org>
llvm-svn: 301582

polly/lib/Analysis/ScopInfo.cpp

diff --git a/polly/lib/Analysis/ScopInfo.cpp b/polly/lib/Analysis/ScopInfo.cpp
index cfc2297..b6a09a9 100644
--- a/polly/lib/Analysis/ScopInfo.cpp
+++ b/polly/lib/Analysis/ScopInfo.cpp
@@ -3737,16 +3737,6 @@
   if (hasNonHoistableBasePtrInScop(Access, Writes))
     return nullptr;
 
-  auto &DL = getFunction().getParent()->getDataLayout();
-  if (isSafeToLoadUnconditionally(LI->getPointerOperand(), LI->getAlignment(),
-                                  DL))
-    return isl_set_empty(getParamSpace());
-
-  // Skip accesses in non-affine subregions as they might not be executed
-  // under the same condition as the entry of the non-affine subregion.
-  if (BB != LI->getParent())
-    return nullptr;
-
   isl_map *AccessRelation = Access->getAccessRelation();
   assert(!isl_map_is_empty(AccessRelation));
 
@@ -3757,10 +3747,25 @@
   }
 
   AccessRelation = isl_map_intersect_domain(AccessRelation, Stmt.getDomain());
-  isl_set *AccessRange = isl_map_range(AccessRelation);
+  isl_set *SafeToLoad;
+
+  auto &DL = getFunction().getParent()->getDataLayout();
+  if (isSafeToLoadUnconditionally(LI->getPointerOperand(), LI->getAlignment(),
+                                  DL)) {
+    SafeToLoad =
+        isl_set_universe(isl_space_range(isl_map_get_space(AccessRelation)));
+    isl_map_free(AccessRelation);
+  } else if (BB != LI->getParent()) {
+    // Skip accesses in non-affine subregions as they might not be executed
+    // under the same condition as the entry of the non-affine subregion.
+    isl_map_free(AccessRelation);
+    return nullptr;
+  } else {
+    SafeToLoad = isl_map_range(AccessRelation);
+  }
 
   isl_union_map *Written = isl_union_map_intersect_range(
-      isl_union_map_copy(Writes), isl_union_set_from_set(AccessRange));
+      isl_union_map_copy(Writes), isl_union_set_from_set(SafeToLoad));
   auto *WrittenCtx = isl_union_map_params(Written);
   bool IsWritten = !isl_set_is_empty(WrittenCtx);