[llvm] r298217 - [JumpThreading] Perform phi-translation in SimplifyPartiallyRedundantLoad.

[Xin Tong via llvm-commits]

Author: trentxintong
Date: Sun Mar 19 10:30:53 2017
New Revision: 298217

URL: http://llvm.org/viewvc/llvm-project?rev=298217&view=rev
Log:
[JumpThreading] Perform phi-translation in SimplifyPartiallyRedundantLoad.

Summary:
In case we are loading on a phi-load in SimplifyPartiallyRedundantLoad.
Try to phi translate it into incoming values in the predecessors before
we search for available loads.

This needs https://reviews.llvm.org/D30524

Reviewers: davide, sanjoy, efriedma, dberlin, rengolin

Reviewed By: dberlin

Subscribers: junbuml, llvm-commits

Differential Revision: https://reviews.llvm.org/D30543

Modified:
    llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp
    llvm/trunk/test/Transforms/JumpThreading/thread-loads.ll

Modified: llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp?rev=298217&r1=298216&r2=298217&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp Sun Mar 19 10:30:53 2017
@@ -931,6 +931,14 @@ bool JumpThreadingPass::ProcessImpliedCo
   return false;
 }
 
+/// Return true if Op is an instruction defined in the given block.
+static bool isOpDefinedInBlock(Value *Op, BasicBlock *BB) {
+  if (Instruction *OpInst = dyn_cast<Instruction>(Op))
+    if (OpInst->getParent() == BB)
+      return true;
+  return false;
+}
+
 /// SimplifyPartiallyRedundantLoad - If LI is an obviously partially redundant
 /// load instruction, eliminate it by replacing it with a PHI node.  This is an
 /// important optimization that encourages jump threading, and needs to be run
@@ -953,11 +961,10 @@ bool JumpThreadingPass::SimplifyPartiall
 
   Value *LoadedPtr = LI->getOperand(0);
 
-  // If the loaded operand is defined in the LoadBB, it can't be available.
-  // TODO: Could do simple PHI translation, that would be fun :)
-  if (Instruction *PtrOp = dyn_cast<Instruction>(LoadedPtr))
-    if (PtrOp->getParent() == LoadBB)
-      return false;
+  // If the loaded operand is defined in the LoadBB and its not a phi,
+  // it can't be available in predecessors.
+  if (isOpDefinedInBlock(LoadedPtr, LoadBB) && !isa<PHINode>(LoadedPtr))
+    return false;
 
   // Scan a few instructions up from the load, to see if it is obviously live at
   // the entry to its block.
@@ -1008,23 +1015,31 @@ bool JumpThreadingPass::SimplifyPartiall
     if (!PredsScanned.insert(PredBB).second)
       continue;
 
-    // Scan the predecessor to see if the value is available in the pred.
     BBIt = PredBB->end();
     unsigned NumScanedInst = 0;
-    Value *PredAvailable = FindAvailableLoadedValue(
-        LI, PredBB, BBIt, DefMaxInstsToScan, AA, &IsLoadCSE, &NumScanedInst);
+    Value *PredAvailable = nullptr;
+    // NOTE: We don't CSE load that is volatile or anything stronger than
+    // unordered, that should have been checked when we entered the function.
+    assert(LI->isUnordered() && "Attempting to CSE volatile or atomic loads");
+    // If this is a load on a phi pointer, phi-translate it and search
+    // for available load/store to the pointer in predecessors.
+    Value *Ptr = LoadedPtr->DoPHITranslation(LoadBB, PredBB);
+    PredAvailable = FindAvailablePtrLoadStore(
+        Ptr, LI->getType(), LI->isAtomic(), PredBB, BBIt, DefMaxInstsToScan,
+        nullptr, &IsLoadCSE, &NumScanedInst);
 
-    // If PredBB has a single predecessor, continue scanning through the single
-    // predecessor.
+    // If PredBB has a single predecessor, continue scanning through the
+    // single precessor.
     BasicBlock *SinglePredBB = PredBB;
     while (!PredAvailable && SinglePredBB && BBIt == SinglePredBB->begin() &&
            NumScanedInst < DefMaxInstsToScan) {
       SinglePredBB = SinglePredBB->getSinglePredecessor();
       if (SinglePredBB) {
         BBIt = SinglePredBB->end();
-        PredAvailable = FindAvailableLoadedValue(
-            LI, SinglePredBB, BBIt, (DefMaxInstsToScan - NumScanedInst), AA,
-            &IsLoadCSE, &NumScanedInst);
+        PredAvailable = FindAvailablePtrLoadStore(
+            Ptr, LI->getType(), LI->isAtomic(), SinglePredBB, BBIt,
+            (DefMaxInstsToScan - NumScanedInst), nullptr, &IsLoadCSE,
+            &NumScanedInst);
       }
     }
 
@@ -1087,10 +1102,10 @@ bool JumpThreadingPass::SimplifyPartiall
   if (UnavailablePred) {
     assert(UnavailablePred->getTerminator()->getNumSuccessors() == 1 &&
            "Can't handle critical edge here!");
-    LoadInst *NewVal =
-        new LoadInst(LoadedPtr, LI->getName() + ".pr", false,
-                     LI->getAlignment(), LI->getOrdering(), LI->getSynchScope(),
-                     UnavailablePred->getTerminator());
+    LoadInst *NewVal = new LoadInst(
+        LoadedPtr->DoPHITranslation(LoadBB, UnavailablePred),
+        LI->getName() + ".pr", false, LI->getAlignment(), LI->getOrdering(),
+        LI->getSynchScope(), UnavailablePred->getTerminator());
     NewVal->setDebugLoc(LI->getDebugLoc());
     if (AATags)
       NewVal->setAAMetadata(AATags);

Modified: llvm/trunk/test/Transforms/JumpThreading/thread-loads.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/JumpThreading/thread-loads.ll?rev=298217&r1=298216&r2=298217&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/JumpThreading/thread-loads.ll (original)
+++ llvm/trunk/test/Transforms/JumpThreading/thread-loads.ll Sun Mar 19 10:30:53 2017
@@ -490,6 +490,41 @@ declare void @fn2(i64)
 declare void @fn3(i64)
 
 
+; Make sure we phi-translate and make the partially redundant load in
+; merge fully redudant and then we can jump-thread the block with the
+; store.
+;
+; CHECK-LABEL: define i32 @phi_translate_partial_redundant_loads(i32, i32*, i32*
+; CHECK: merge.thread:
+; CHECK: store
+; CHECK: br label %left_x
+;
+; CHECK: left_x:
+; CHECK-NEXT: ret i32 20
+define i32 @phi_translate_partial_redundant_loads(i32, i32*, i32*)  {
+  %cmp0 = icmp ne i32 %0, 0
+  br i1 %cmp0, label %left, label %right
+
+left:
+  store i32 1, i32* %1, align 4
+  br label %merge
+
+right:
+  br label %merge
+
+merge:
+  %phiptr = phi i32* [ %1, %left ], [ %2, %right ]
+  %newload = load i32, i32* %phiptr, align 4
+  %cmp1 = icmp slt i32 %newload, 5
+  br i1 %cmp1, label %left_x, label %right_x
+
+left_x:
+  ret i32 20
+
+right_x:
+  ret i32 10
+}
+
 !0 = !{!3, !3, i64 0}
 !1 = !{!"omnipotent char", !2}
 !2 = !{!"Simple C/C++ TBAA"}