[CodeGen] Support partial write accesses.

Allow the BlockGenerator to generate memory writes that are not defined
over the complete statement domain, but only over a subset of it. It
generates a condition that evaluates to 1 if executing the subdomain,
and only then execute the access.

Only write accesses are supported. Read accesses would require a PHINode
which has a value if the access is not executed.

Partial write makes DeLICM able to apply mappings that are not defined
over the entire domain (for instance, a branch that leaves a loop with
a PHINode in its header; a MemoryKind::PHI write when leaving is never
read by its PHI read).

Differential Revision: https://reviews.llvm.org/D33255

llvm-svn: 303517

1 files changed, 3 insertions, 2 deletions

diff --git a/polly/lib/Exchange/JSONExporter.cpp b/polly/lib/Exchange/JSONExporter.cpp
index 21722d08e6b..0e8ff564eaa 100644
--- a/polly/lib/Exchange/JSONExporter.cpp
+++ b/polly/lib/Exchange/JSONExporter.cpp
@@ -446,8 +446,9 @@ bool JSONImporter::importAccesses(Scop &S, Json::Value &JScop,
       CurrentAccessDomain =
           isl_set_intersect_params(CurrentAccessDomain, S.getContext());
 
-      if (isl_set_is_subset(CurrentAccessDomain, NewAccessDomain) ==
-          isl_bool_false) {
+      if (MA->isRead() &&
+          isl_set_is_subset(CurrentAccessDomain, NewAccessDomain) ==
+              isl_bool_false) {
         errs() << "Mapping not defined for all iteration domain elements\n";
         isl_set_free(CurrentAccessDomain);
         isl_set_free(NewAccessDomain);