[PATCH] D71539: [SCEV] Look through trivial PHIs (WIP).

[Florian Hahn via Phabricator via llvm-commits]

fhahn updated this revision to Diff 277794.
fhahn added a comment.

Rebase


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D71539/new/

https://reviews.llvm.org/D71539

Files:
  llvm/lib/Analysis/ScalarEvolution.cpp
  llvm/test/Analysis/ScalarEvolution/solve-quadratic-i1.ll
  llvm/test/Analysis/ScalarEvolution/solve-quadratic-overflow.ll


Index: llvm/test/Analysis/ScalarEvolution/solve-quadratic-overflow.ll
===================================================================
--- llvm/test/Analysis/ScalarEvolution/solve-quadratic-overflow.ll
+++ llvm/test/Analysis/ScalarEvolution/solve-quadratic-overflow.ll
@@ -12,11 +12,11 @@
 ; CHECK-NEXT:   %v3 = mul i16 %v2, %v2
 ; CHECK-NEXT:   -->  {1,+,3,+,2}<%b1> U: full-set S: full-set         Exits: 0               LoopDispositions: { %b1: Computable }
 ; CHECK-NEXT:   %v5 = phi i16 [ %v2, %b1 ]
-; CHECK-NEXT:   -->  %v5 U: [-256,0) S: [-256,0)
+; CHECK-NEXT:   -->  {-1,+,-1}<%b1> U: [-256,0) S: [-256,0)  -->  -256 U: [-256,-255) S: [-256,-255)
 ; CHECK-NEXT:   %v6 = phi i16 [ %v3, %b1 ]
-; CHECK-NEXT:   -->  %v6 U: full-set S: full-set
+; CHECK-NEXT:   -->  {1,+,3,+,2}<%b1> U: full-set S: full-set  -->  0 U: [0,1) S: [0,1)
 ; CHECK-NEXT:   %v7 = sext i16 %v5 to i32
-; CHECK-NEXT:   -->  (sext i16 %v5 to i32) U: [-256,0) S: [-256,0)
+; CHECK-NEXT:   -->  {-1,+,-1}<nsw><%b1> U: [-256,0) S: [-256,0)  -->  -256 U: [-256,-255) S: [-256,-255)
 ; CHECK-NEXT: Determining loop execution counts for: @f0
 ; CHECK-NEXT: Loop %b1: backedge-taken count is 255
 ; CHECK-NEXT: Loop %b1: max backedge-taken count is 255
Index: llvm/test/Analysis/ScalarEvolution/solve-quadratic-i1.ll
===================================================================
--- llvm/test/Analysis/ScalarEvolution/solve-quadratic-i1.ll
+++ llvm/test/Analysis/ScalarEvolution/solve-quadratic-i1.ll
@@ -57,9 +57,9 @@
 ; CHECK-NEXT:   %v6 = add nuw nsw i32 %v1, 1
 ; CHECK-NEXT:   -->  {4,+,1}<nuw><nsw><%b1> U: [4,7) S: [4,7)         Exits: 6                LoopDispositions: { %b1: Computable }
 ; CHECK-NEXT:   %v7 = phi i32 [ %v1, %b1 ]
-; CHECK-NEXT:   -->  %v7 U: [3,6) S: [3,6)
+; CHECK-NEXT:   -->  {3,+,1}<nuw><nsw><%b1> U: [3,6) S: [3,6)  -->  5 U: [5,6) S: [5,6)
 ; CHECK-NEXT:   %v8 = phi i16 [ %v3, %b1 ]
-; CHECK-NEXT:   -->  %v8 U: full-set S: full-set
+; CHECK-NEXT:   -->  {3,+,4,+,1}<%b1> U: full-set S: full-set  -->  12 U: [12,13) S: [12,13)
 ; CHECK-NEXT: Determining loop execution counts for: @f1
 ; CHECK-NEXT: Loop %b3: <multiple exits> Unpredictable backedge-taken count.
 ; CHECK-NEXT: Loop %b3: Unpredictable max backedge-taken count.
Index: llvm/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolution.cpp
+++ llvm/lib/Analysis/ScalarEvolution.cpp
@@ -3689,7 +3689,6 @@
   }
   return false;
 }
-
 /// Return an existing SCEV if it exists, otherwise analyze the expression and
 /// create a new one.
 const SCEV *ScalarEvolution::getSCEV(Value *V) {
@@ -3717,7 +3716,10 @@
       // If V is GetElementPtrInst, don't save Stripped -> {V, offset}
       // because it may generate add/sub instead of GEP in SCEV expansion.
       if (Offset != nullptr && !isa<SCEVUnknown>(Stripped) &&
-          !isa<GetElementPtrInst>(V))
+          !isa<GetElementPtrInst>(V) &&
+          (!isa<PHINode>(V) ||
+           SimplifyInstruction(cast<PHINode>(V),
+                               {getDataLayout(), &TLI, &DT, &AC}) == V))
         ExprValueMap[Stripped].insert({V, Offset});
     }
   }
@@ -5115,13 +5117,8 @@
   if (const SCEV *S = createNodeFromSelectLikePHI(PN))
     return S;
 
-  // If the PHI has a single incoming value, follow that value, unless the
-  // PHI's incoming blocks are in a different loop, in which case doing so
-  // risks breaking LCSSA form. Instcombine would normally zap these, but
-  // it doesn't have DominatorTree information, so it may miss cases.
   if (Value *V = SimplifyInstruction(PN, {getDataLayout(), &TLI, &DT, &AC}))
-    if (LI.replacementPreservesLCSSAForm(PN, V))
-      return getSCEV(V);
+    return getSCEV(V);
 
   // If it's not a loop phi, we can't handle it yet.
   return getUnknown(PN);
@@ -6561,7 +6558,9 @@
         // count information isn't going to change anything. In the later
         // case, createNodeForPHI will perform the necessary updates on its
         // own when it gets to that point.
-        if (!isa<PHINode>(I) || !isa<SCEVUnknown>(Old)) {
+        if ((!isa<PHINode>(I) ||
+             cast<PHINode>(I)->getNumIncomingValues() == 1) ||
+            !isa<SCEVUnknown>(Old)) {
           eraseValueFromMap(It->first);
           forgetMemoizedResults(Old);
         }


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