[PATCH] D23920: [StatepointsForGC] Identify values for rematerialization in presence of PHI

[Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rL279975: [StatepointsForGC] Rematerialize in the presence of PHIs (authored by annat).

Changed prior to commit:
  https://reviews.llvm.org/D23920?vs=69438&id=69573#toc

Repository:
  rL LLVM

https://reviews.llvm.org/D23920

Files:
  llvm/trunk/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
  llvm/trunk/test/Transforms/RewriteStatepointsForGC/rematerialize-derived-pointers.ll

Index: llvm/trunk/test/Transforms/RewriteStatepointsForGC/rematerialize-derived-pointers.ll
===================================================================
--- llvm/trunk/test/Transforms/RewriteStatepointsForGC/rematerialize-derived-pointers.ll
+++ llvm/trunk/test/Transforms/RewriteStatepointsForGC/rematerialize-derived-pointers.ll
@@ -259,3 +259,40 @@
   call void @use_obj32(i32 addrspace(1)* %ptr.gep11)
   ret void
 }
+
+
+declare i32 addrspace(1)* @new_instance() nounwind "gc-leaf-function"
+
+; remat the gep in presence of base pointer which is a phi node.
+; FIXME: We should remove the extra basephi.base as well.
+define void @contains_basephi(i1 %cond) gc "statepoint-example" {
+; CHECK-LABEL: contains_basephi
+entry:
+  %base1 = call i32 addrspace(1)* @new_instance()
+  %base2 = call i32 addrspace(1)* @new_instance()
+  br i1 %cond, label %here, label %there
+
+here:
+  br label %merge
+
+there:
+  br label %merge
+
+merge:
+  ; CHECK: %basephi.base = phi i32 addrspace(1)* [ %base1, %here ], [ %base2, %there ], !is_base_value !0
+  ; CHECK: %basephi = phi i32 addrspace(1)* [ %base1, %here ], [ %base2, %there ]
+  ; CHECK: %ptr.gep = getelementptr i32, i32 addrspace(1)* %basephi, i32 15
+  ; CHECK: %statepoint_token = call token (i64, i32, void ()*, i32, i32, ...) @llvm.experimental.gc.statepoint
+  ; CHECK: %basephi.base.relocated = call coldcc i8 addrspace(1)* @llvm.experimental.gc.relocate.p1i8(token %statepoint_token, i32 7, i32 7) ; (%basephi.base, %basephi.base)
+  ; CHECK: %basephi.base.relocated.casted = bitcast i8 addrspace(1)* %basephi.base.relocated to i32 addrspace(1)*
+  ; CHECK: %ptr.gep.remat = getelementptr i32, i32 addrspace(1)* %basephi, i32 15
+  ; CHECK: call void @use_obj32(i32 addrspace(1)* %ptr.gep.remat)
+
+
+
+  %basephi = phi i32 addrspace(1)* [ %base1, %here ], [ %base2, %there ]
+  %ptr.gep = getelementptr i32, i32 addrspace(1)* %basephi, i32 15
+  call void @do_safepoint() ["deopt"() ]
+  call void @use_obj32(i32 addrspace(1)* %ptr.gep)
+  ret void
+}
Index: llvm/trunk/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
+++ llvm/trunk/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
@@ -1797,6 +1797,41 @@
     return true;
   }
 
+  // Check for same values, when both BaseValue and CurrentValue are phi nodes.
+  // PHI nodes that have the same incoming values, and belonging to the same
+  // basic blocks are essentially the same SSA value.  Such an example of same
+  // BaseValue, CurrentValue phis is created by findBasePointer, when a phi has
+  // incoming values with different base pointers. This phi is marked as
+  // conflict, and hence an additional phi with the same incoming values get
+  // generated. We need to identify the BaseValue (.base version of phi) and
+  // CurrentValue (the phi node itself) as the same, so that we can
+  // rematerialize the gep and casts below.
+  if (PHINode *CurrentPhi = dyn_cast<PHINode>(CurrentValue))
+    if (PHINode *BasePhi = dyn_cast<PHINode>(BaseValue)) {
+      auto PhiNum = CurrentPhi->getNumIncomingValues();
+      if (PhiNum != BasePhi->getNumIncomingValues() ||
+          CurrentPhi->getParent() != BasePhi->getParent())
+        return false;
+      // Map of incoming values and their corresponding basic blocks of
+      // CurrentPhi.
+      SmallDenseMap<Value *, BasicBlock *, 8> CurrentIncomingValues;
+      for (unsigned i = 0; i < PhiNum; i++)
+        CurrentIncomingValues[CurrentPhi->getIncomingValue(i)] =
+            CurrentPhi->getIncomingBlock(i);
+
+      // Both current and base PHIs should have same incoming values and
+      // the same basic blocks corresponding to the incoming values.
+      for (unsigned i = 0; i < PhiNum; i++) {
+        auto CIVI = CurrentIncomingValues.find(BasePhi->getIncomingValue(i));
+        if (CIVI == CurrentIncomingValues.end())
+          return false;
+        BasicBlock *CurrentIncomingBB = CIVI->second;
+        if (CurrentIncomingBB != BasePhi->getIncomingBlock(i))
+          return false;
+      }
+      return true;
+    }
+
   if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurrentValue)) {
     ChainToBase.push_back(GEP);
     return findRematerializableChainToBasePointer(ChainToBase,


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