[PATCH] D110378: [CodeMoverUtils] Enhance isSafeToMoveBefore() when moving BBs

[Congzhe Cao via Phabricator via llvm-commits]

congzhe updated this revision to Diff 374717.

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D110378/new/

https://reviews.llvm.org/D110378

Files:
  llvm/include/llvm/Transforms/Utils/CodeMoverUtils.h
  llvm/lib/Transforms/Utils/CodeMoverUtils.cpp
  llvm/unittests/Transforms/Utils/CodeMoverUtilsTest.cpp


Index: llvm/unittests/Transforms/Utils/CodeMoverUtilsTest.cpp
===================================================================
--- llvm/unittests/Transforms/Utils/CodeMoverUtilsTest.cpp
+++ llvm/unittests/Transforms/Utils/CodeMoverUtilsTest.cpp
@@ -601,6 +601,8 @@
                    br label %for.latch
                  for.latch:
                    %cmp = icmp slt i64 %inc, %N
+                   %add = add i64 100, %N
+                   %add2 = add i64 %add, %N
                    br i1 %cmp, label %for.body, label %for.end
                  for.end:
                    ret void
@@ -611,10 +613,18 @@
           DependenceInfo &DI) {
         Instruction *IncInst = getInstructionByName(F, "inc");
         Instruction *CmpInst = getInstructionByName(F, "cmp");
+        BasicBlock *BB0 = getBasicBlockByName(F, "for.body");
+        BasicBlock *BB1 = getBasicBlockByName(F, "for.latch");
 
         // Can move as the incoming block of %inc for %i (%for.latch) dominated
         // by %cmp.
         EXPECT_TRUE(isSafeToMoveBefore(*IncInst, *CmpInst, DT, &PDT, &DI));
+
+        // Can move as the operands of instructions in BB1 either dominate
+        // InsertPoint or appear before that instruction, e.g., %add appears
+        // before %add2 although %add does not dominate InsertPoint.
+        EXPECT_TRUE(
+            isSafeToMoveBefore(*BB1, *BB0->getTerminator(), DT, &PDT, &DI));
       });
 }
 
Index: llvm/lib/Transforms/Utils/CodeMoverUtils.cpp
===================================================================
--- llvm/lib/Transforms/Utils/CodeMoverUtils.cpp
+++ llvm/lib/Transforms/Utils/CodeMoverUtils.cpp
@@ -309,7 +309,7 @@
 
 bool llvm::isSafeToMoveBefore(Instruction &I, Instruction &InsertPoint,
                               DominatorTree &DT, const PostDominatorTree *PDT,
-                              DependenceInfo *DI) {
+                              DependenceInfo *DI, bool CheckForEntireBlock) {
   // Skip tests when we don't have PDT or DI
   if (!PDT || !DI)
     return false;
@@ -339,9 +339,17 @@
           return false;
   if (!DT.dominates(&I, &InsertPoint))
     for (const Value *Op : I.operands())
-      if (auto *OpInst = dyn_cast<Instruction>(Op))
-        if (&InsertPoint == OpInst || !DT.dominates(OpInst, &InsertPoint))
+      if (auto *OpInst = dyn_cast<Instruction>(Op)) {
+        if (&InsertPoint == OpInst)
+          return false;
+        // If OpInst is an instruction that appears earlier in the same BB as
+        // I, then it is okay to move since OpInst will still be available.
+        if (CheckForEntireBlock && I.getParent() == OpInst->getParent() &&
+            DT.dominates(OpInst, &I))
+          continue;
+        if (!DT.dominates(OpInst, &InsertPoint))
           return false;
+      }
 
   DT.updateDFSNumbers();
   const bool MoveForward = domTreeLevelBefore(&DT, &I, &InsertPoint);
@@ -393,7 +401,8 @@
     if (BB.getTerminator() == &I)
       return true;
 
-    return isSafeToMoveBefore(I, InsertPoint, DT, PDT, DI);
+    return isSafeToMoveBefore(I, InsertPoint, DT, PDT, DI,
+                              /*CheckForEntireBlock=*/true);
   });
 }
 
Index: llvm/include/llvm/Transforms/Utils/CodeMoverUtils.h
===================================================================
--- llvm/include/llvm/Transforms/Utils/CodeMoverUtils.h
+++ llvm/include/llvm/Transforms/Utils/CodeMoverUtils.h
@@ -40,7 +40,8 @@
 bool isSafeToMoveBefore(Instruction &I, Instruction &InsertPoint,
                         DominatorTree &DT,
                         const PostDominatorTree *PDT = nullptr,
-                        DependenceInfo *DI = nullptr);
+                        DependenceInfo *DI = nullptr,
+                        bool CheckForEntireBlock = false);
 
 /// Return true if all instructions (except the terminator) in \p BB can be
 /// safely moved before \p InsertPoint.


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