[DeLICM] Use input access heuristic for mapped PHI WRITEs.

As with the scalar operand of the initial StoreInst, also use input
accesses when searching for new opportunities after mapping a
PHI write.

The same rational applies here: After LICM has been applied, the
promoted value will either be an instruction in the same statement
(in which case we fall back to try every scalar access of the
statement), or in another statement such that there will be such
an input access. In the latter case other scalars cannot have
originated from the same register promotion, at least not by LICM.

This mostly helps to decrease compilation time and makes debugging
easier by not pursuing unpromising routes. In some circumstances,
it may change the compiler's output.

llvm-svn: 302839

1 files changed, 18 insertions, 3 deletions

diff --git a/polly/lib/Transform/DeLICM.cpp b/polly/lib/Transform/DeLICM.cpp
index 7bcb0726632..a6ef8cdfbbb 100644
--- a/polly/lib/Transform/DeLICM.cpp
+++ b/polly/lib/Transform/DeLICM.cpp
@@ -1996,9 +1996,24 @@ private:
       if (SAI->isPHIKind()) {
         if (!tryMapPHI(SAI, EltTarget))
           continue;
-        // Add inputs of all incoming statements to the worklist.
-        for (auto *PHIWrite : DefUse.getPHIIncomings(SAI))
-          ProcessAllIncoming(PHIWrite->getStatement());
+        // Add inputs of all incoming statements to the worklist. Prefer the
+        // input accesses of the incoming blocks.
+        for (auto *PHIWrite : DefUse.getPHIIncomings(SAI)) {
+          auto *PHIWriteStmt = PHIWrite->getStatement();
+          bool FoundAny = false;
+          for (auto Incoming : PHIWrite->getIncoming()) {
+            auto *IncomingInputMA =
+                PHIWriteStmt->lookupInputAccessOf(Incoming.second);
+            if (!IncomingInputMA)
+              continue;
+
+            Worklist.push_back(IncomingInputMA);
+            FoundAny = true;
+          }
+
+          if (!FoundAny)
+            ProcessAllIncoming(PHIWrite->getStatement());
+        }
 
         AnyMapped = true;
         continue;