Teach SCEVExpander's visitAddRecExpr to reuse an existing canonical

induction variable when the addrec to be expanded does not require
a wider type. This eliminates the need for IndVarSimplify to
micro-manage SCEV expansions, because SCEVExpander now
automatically expands them in the form that IndVarSimplify considers
to be canonical. (LSR still micro-manages its SCEV expansions,
because it's optimizing for the target, rather than for
other optimizations.)

Also, this uses the new getAnyExtendExpr, which has more clever
expression simplification logic than the IndVarSimplify code it
replaces, and this cleans up some ugly expansions in code such as
the included masked-iv.ll testcase.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73294 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 51 insertions, 8 deletions

diff --git a/lib/Analysis/ScalarEvolutionExpander.cpp b/lib/Analysis/ScalarEvolutionExpander.cpp
index 477d88e..e1f8fa4 100644
--- a/lib/Analysis/ScalarEvolutionExpander.cpp
+++ b/lib/Analysis/ScalarEvolutionExpander.cpp
@@ -16,6 +16,7 @@
 #include "llvm/Analysis/ScalarEvolutionExpander.h"
 #include "llvm/Analysis/LoopInfo.h"
 #include "llvm/Target/TargetData.h"
+#include "llvm/ADT/STLExtras.h"
 using namespace llvm;
 
 /// InsertCastOfTo - Insert a cast of V to the specified type, doing what
@@ -442,6 +443,34 @@ Value *SCEVExpander::visitAddRecExpr(const SCEVAddRecExpr *S) {
   const Type *Ty = SE.getEffectiveSCEVType(S->getType());
   const Loop *L = S->getLoop();
 
+  // First check for an existing canonical IV in a suitable type.
+  PHINode *CanonicalIV = 0;
+  if (PHINode *PN = L->getCanonicalInductionVariable())
+    if (SE.isSCEVable(PN->getType()) &&
+        isa<IntegerType>(SE.getEffectiveSCEVType(PN->getType())) &&
+        SE.getTypeSizeInBits(PN->getType()) >= SE.getTypeSizeInBits(Ty))
+      CanonicalIV = PN;
+
+  // Rewrite an AddRec in terms of the canonical induction variable, if
+  // its type is more narrow.
+  if (CanonicalIV &&
+      SE.getTypeSizeInBits(CanonicalIV->getType()) >
+      SE.getTypeSizeInBits(Ty)) {
+    SCEVHandle Start = SE.getAnyExtendExpr(S->getStart(),
+                                           CanonicalIV->getType());
+    SCEVHandle Step = SE.getAnyExtendExpr(S->getStepRecurrence(SE),
+                                          CanonicalIV->getType());
+    Value *V = expand(SE.getAddRecExpr(Start, Step, S->getLoop()));
+    BasicBlock::iterator SaveInsertPt = getInsertionPoint();
+    BasicBlock::iterator NewInsertPt =
+      next(BasicBlock::iterator(cast<Instruction>(V)));
+    while (isa<PHINode>(NewInsertPt)) ++NewInsertPt;
+    V = expandCodeFor(SE.getTruncateExpr(SE.getUnknown(V), Ty), 0,
+                      NewInsertPt);
+    setInsertionPoint(SaveInsertPt);
+    return V;
+  }
+
   // {X,+,F} --> X + {0,+,F}
   if (!S->getStart()->isZero()) {
     std::vector<SCEVHandle> NewOps(S->getOperands());
@@ -475,6 +504,14 @@ Value *SCEVExpander::visitAddRecExpr(const SCEVAddRecExpr *S) {
   // {0,+,1} --> Insert a canonical induction variable into the loop!
   if (S->isAffine() &&
       S->getOperand(1) == SE.getIntegerSCEV(1, Ty)) {
+    // If there's a canonical IV, just use it.
+    if (CanonicalIV) {
+      assert(Ty == SE.getEffectiveSCEVType(CanonicalIV->getType()) &&
+             "IVs with types different from the canonical IV should "
+             "already have been handled!");
+      return CanonicalIV;
+    }
+
     // Create and insert the PHI node for the induction variable in the
     // specified loop.
     BasicBlock *Header = L->getHeader();
@@ -502,18 +539,16 @@ Value *SCEVExpander::visitAddRecExpr(const SCEVAddRecExpr *S) {
     return PN;
   }
 
+  // {0,+,F} --> {0,+,1} * F
   // Get the canonical induction variable I for this loop.
-  Value *I = getOrInsertCanonicalInductionVariable(L, Ty);
+  Value *I = CanonicalIV ?
+             CanonicalIV :
+             getOrInsertCanonicalInductionVariable(L, Ty);
 
   // If this is a simple linear addrec, emit it now as a special case.
   if (S->isAffine()) {   // {0,+,F} --> i*F
     Value *F = expandCodeFor(S->getOperand(1), Ty);
-    
-    // If the step is by one, just return the inserted IV.
-    if (ConstantInt *CI = dyn_cast<ConstantInt>(F))
-      if (CI->getValue() == 1)
-        return I;
-    
+
     // If the insert point is directly inside of the loop, emit the multiply at
     // the insert point.  Otherwise, L is a loop that is a parent of the insert
     // point loop.  If we can, move the multiply to the outer most loop that it
@@ -548,9 +583,17 @@ Value *SCEVExpander::visitAddRecExpr(const SCEVAddRecExpr *S) {
   // into this folder.
   SCEVHandle IH = SE.getUnknown(I);   // Get I as a "symbolic" SCEV.
 
-  SCEVHandle V = S->evaluateAtIteration(IH, SE);
+  // Promote S up to the canonical IV type, if the cast is foldable.
+  SCEVHandle NewS = S;
+  SCEVHandle Ext = SE.getNoopOrAnyExtend(S, I->getType());
+  if (isa<SCEVAddRecExpr>(Ext))
+    NewS = Ext;
+
+  SCEVHandle V = cast<SCEVAddRecExpr>(NewS)->evaluateAtIteration(IH, SE);
   //cerr << "Evaluated: " << *this << "\n     to: " << *V << "\n";
 
+  // Truncate the result down to the original type, if needed.
+  SCEVHandle T = SE.getTruncateOrNoop(V, Ty);
   return expand(V);
 }