[PATCH] D12958: Refactor computeKnownBits alignment handling code

[Artur Pilipenko via llvm-commits]

apilipenko created this revision.
apilipenko added reviewers: hfinkel, reames.
apilipenko added a subscriber: llvm-commits.

This is a preparatory refactoring for using new alignment attributes/metadata (D12844, D12853) in computeKnownBits.

http://reviews.llvm.org/D12958

Files:
  lib/Analysis/ValueTracking.cpp

Index: lib/Analysis/ValueTracking.cpp
===================================================================
--- lib/Analysis/ValueTracking.cpp
+++ lib/Analysis/ValueTracking.cpp
@@ -1462,9 +1462,18 @@
     return;
   }
 
-  // The address of an aligned GlobalValue has trailing zeros.
+  // Start out not knowing anything.
+  KnownZero.clearAllBits(); KnownOne.clearAllBits();
+
+  // Limit search depth.
+  // All recursive calls that increase depth must come after this.
+  if (Depth == MaxDepth)
+    return;
+
+  // If V is a pointer check if we know it's alignment
+  unsigned Align = 0;
   if (auto *GO = dyn_cast<GlobalObject>(V)) {
-    unsigned Align = GO->getAlignment();
+    Align = GO->getAlignment();
     if (Align == 0) {
       if (auto *GVar = dyn_cast<GlobalVariable>(GO)) {
         Type *ObjectType = GVar->getType()->getElementType();
@@ -1479,49 +1488,20 @@
         }
       }
     }
-    if (Align > 0)
-      KnownZero = APInt::getLowBitsSet(BitWidth,
-                                       countTrailingZeros(Align));
-    else
-      KnownZero.clearAllBits();
-    KnownOne.clearAllBits();
-    return;
-  }
-
-  if (Argument *A = dyn_cast<Argument>(V)) {
-    unsigned Align = A->getType()->isPointerTy() ? A->getParamAlignment() : 0;
+  } else if (Argument *A = dyn_cast<Argument>(V)) {
+    Align = A->getType()->isPointerTy() ? A->getParamAlignment() : 0;
 
     if (!Align && A->hasStructRetAttr()) {
       // An sret parameter has at least the ABI alignment of the return type.
       Type *EltTy = cast<PointerType>(A->getType())->getElementType();
       if (EltTy->isSized())
         Align = DL.getABITypeAlignment(EltTy);
     }
-
-    if (Align)
-      KnownZero = APInt::getLowBitsSet(BitWidth, countTrailingZeros(Align));
-    else
-      KnownZero.clearAllBits();
-    KnownOne.clearAllBits();
-
-    // Don't give up yet... there might be an assumption that provides more
-    // information...
-    computeKnownBitsFromAssume(V, KnownZero, KnownOne, DL, Depth, Q);
-
-    // Or a dominating condition for that matter
-    if (EnableDomConditions && Depth <= DomConditionsMaxDepth)
-      computeKnownBitsFromDominatingCondition(V, KnownZero, KnownOne, DL,
-                                              Depth, Q);
-    return;
   }
 
-  // Start out not knowing anything.
-  KnownZero.clearAllBits(); KnownOne.clearAllBits();
-
-  // Limit search depth.
-  // All recursive calls that increase depth must come after this.
-  if (Depth == MaxDepth)
-    return;
+  // Aligned pointers have trailing zeros
+  if (Align)
+    KnownZero = APInt::getLowBitsSet(BitWidth, countTrailingZeros(Align));
 
   // A weak GlobalAlias is totally unknown. A non-weak GlobalAlias has
   // the bits of its aliasee.


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