Refactor computeKnownBits alignment handling code

Reviewed By: reames, hfinkel Differential Revision: http://reviews.llvm.org/D12958 llvm-svn: 248892
llvm · Sep 30, 2015 · 029d853 · 029d853
1 parent dade196
commit 029d853
Showing 1 changed file with 38 additions and 53 deletions.
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
@@ -1409,6 +1409,37 @@ static void computeKnownBitsFromOperator(Operator *I, APInt &KnownZero,
   }
 }
 
+static unsigned getAlignment(Value *V, const DataLayout &DL) {
+  unsigned Align = 0;
+  if (auto *GO = dyn_cast<GlobalObject>(V)) {
+    Align = GO->getAlignment();
+    if (Align == 0) {
+      if (auto *GVar = dyn_cast<GlobalVariable>(GO)) {
+        Type *ObjectType = GVar->getType()->getElementType();
+        if (ObjectType->isSized()) {
+          // If the object is defined in the current Module, we'll be giving
+          // it the preferred alignment. Otherwise, we have to assume that it
+          // may only have the minimum ABI alignment.
+          if (GVar->isStrongDefinitionForLinker())
+            Align = DL.getPreferredAlignment(GVar);
+          else
+            Align = DL.getABITypeAlignment(ObjectType);
+        }
+      }
+    }
+  } 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);
+    }
+  }
+  return Align;
+}
+
 /// Determine which bits of V are known to be either zero or one and return
 /// them in the KnownZero/KnownOne bit sets.
 ///
@@ -1469,59 +1500,6 @@ void computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne,
     return;
   }
 
-  // The address of an aligned GlobalValue has trailing zeros.
-  if (auto *GO = dyn_cast<GlobalObject>(V)) {
-    unsigned Align = GO->getAlignment();
-    if (Align == 0) {
-      if (auto *GVar = dyn_cast<GlobalVariable>(GO)) {
-        Type *ObjectType = GVar->getType()->getElementType();
-        if (ObjectType->isSized()) {
-          // If the object is defined in the current Module, we'll be giving
-          // it the preferred alignment. Otherwise, we have to assume that it
-          // may only have the minimum ABI alignment.
-          if (GVar->isStrongDefinitionForLinker())
-            Align = DL.getPreferredAlignment(GVar);
-          else
-            Align = DL.getABITypeAlignment(ObjectType);
-        }
-      }
-    }
-    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;
-
-    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();
 
@@ -1541,6 +1519,13 @@ void computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne,
   if (Operator *I = dyn_cast<Operator>(V))
     computeKnownBitsFromOperator(I, KnownZero, KnownOne, DL, Depth, Q);
 
+  // Aligned pointers have trailing zeros - refine KnownZero set
+  if (V->getType()->isPointerTy()) {
+    unsigned Align = getAlignment(V, DL);
+    if (Align)
+      KnownZero |= APInt::getLowBitsSet(BitWidth, countTrailingZeros(Align));
+  }
+
   // computeKnownBitsFromAssume and computeKnownBitsFromDominatingCondition
   // strictly refines KnownZero and KnownOne. Therefore, we run them after
   // computeKnownBitsFromOperator.