[SCEV] Make SCEV or modeling more aggressive.

Use haveNoCommonBitsSet to figure out whether an "or" instruction
is equivalent to addition. This handles more cases than just
checking for a constant on the RHS.

Differential Revision: https://reviews.llvm.org/D32239

llvm-svn: 300746

1 files changed, 6 insertions, 22 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 278b65c68f8..b573374bd64 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -5328,28 +5328,12 @@ const SCEV *ScalarEvolution::createSCEV(Value *V) {
       break;
 
     case Instruction::Or:
-      // If the RHS of the Or is a constant, we may have something like:
-      // X*4+1 which got turned into X*4|1.  Handle this as an Add so loop
-      // optimizations will transparently handle this case.
-      //
-      // In order for this transformation to be safe, the LHS must be of the
-      // form X*(2^n) and the Or constant must be less than 2^n.
-      if (ConstantInt *CI = dyn_cast<ConstantInt>(BO->RHS)) {
-        const SCEV *LHS = getSCEV(BO->LHS);
-        const APInt &CIVal = CI->getValue();
-        if (GetMinTrailingZeros(LHS) >=
-            (CIVal.getBitWidth() - CIVal.countLeadingZeros())) {
-          // Build a plain add SCEV.
-          const SCEV *S = getAddExpr(LHS, getSCEV(CI));
-          // If the LHS of the add was an addrec and it has no-wrap flags,
-          // transfer the no-wrap flags, since an or won't introduce a wrap.
-          if (const SCEVAddRecExpr *NewAR = dyn_cast<SCEVAddRecExpr>(S)) {
-            const SCEVAddRecExpr *OldAR = cast<SCEVAddRecExpr>(LHS);
-            const_cast<SCEVAddRecExpr *>(NewAR)->setNoWrapFlags(
-                OldAR->getNoWrapFlags());
-          }
-          return S;
-        }
+      // Use ValueTracking to check whether this is actually an add.
+      if (haveNoCommonBitsSet(BO->LHS, BO->RHS, getDataLayout(), &AC,
+                              nullptr, &DT)) {
+        // There aren't any common bits set, so the add can't wrap.
+        auto Flags = SCEV::NoWrapFlags(SCEV::FlagNUW | SCEV::FlagNSW);
+        return getAddExpr(getSCEV(BO->LHS), getSCEV(BO->RHS), Flags);
       }
       break;