[EarlyCSE] Don't hide earler invariant.scopes

If we've already established an invariant scope with an earlier generation, we don't want to hide it in the scoped hash table with one with a later generation.  I noticed this when working on the invariant-load handling, but it also applies to the invariant.start case as well.

Without this change, my previous patch for invariant-load regresses some cases, so I'm pushing this without waiting for review.  This is why you don't make last minute tweaks to patches to catch "obvious cases" after it's already been reviewed.  Bad Philip!

llvm-svn: 327655

1 files changed, 8 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Scalar/EarlyCSE.cpp b/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
index 3f70ee49ad9..6f03023cab9 100644
--- a/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
+++ b/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
@@ -799,7 +799,9 @@ bool EarlyCSE::processNode(DomTreeNode *Node) {
         continue;
       auto *CI = cast<CallInst>(Inst);
       MemoryLocation MemLoc = MemoryLocation::getForArgument(CI, 1, TLI);
-      AvailableInvariants.insert(MemLoc, CurrentGeneration);
+      // Don't start a scope if we already have a better one pushed
+      if (!AvailableInvariants.count(MemLoc))
+        AvailableInvariants.insert(MemLoc, CurrentGeneration);
       continue;
     }
 
@@ -888,9 +890,12 @@ bool EarlyCSE::processNode(DomTreeNode *Node) {
       if (MemInst.isInvariantLoad()) {
         // If we pass an invariant load, we know that memory location is
         // indefinitely constant from the moment of first dereferenceability.
-        // We conservatively treat the invariant_load as that moment.
+        // We conservatively treat the invariant_load as that moment.  If we
+        // pass a invariant load after already establishing a scope, don't
+        // restart it since we want to preserve the earliest point seen.
         auto MemLoc = MemoryLocation::get(Inst);
-        AvailableInvariants.insert(MemLoc, CurrentGeneration);
+        if (!AvailableInvariants.count(MemLoc))
+          AvailableInvariants.insert(MemLoc, CurrentGeneration);
       }
 
       // If we have an available version of this load, and if it is the right