commit b45eabcf82da2360b4243c820cd32b706f671c1a
author Craig Topper <craig.topper@gmail.com> Wed Apr 26 16:39:58 2017 +0000
committer Craig Topper <craig.topper@gmail.com> Wed Apr 26 16:39:58 2017 +0000
tree 472f7d59139627ccf935d11f6700cc226a3d4534
parent eec01adde3ac789fe5e032ce34da3b2266830308

[ValueTracking] Introduce a KnownBits struct to wrap the two APInts for computeKnownBits

This patch introduces a new KnownBits struct that wraps the two APInt used by computeKnownBits. This allows us to treat them as more of a unit.

Initially I've just altered the signatures of computeKnownBits and InstCombine's simplifyDemandedBits to pass a KnownBits reference instead of two separate APInt references. I'll do similar to the SelectionDAG version of computeKnownBits/simplifyDemandedBits as a separate patch.

I've added a constructor that allows initializing both APInts to the same bit width with a starting value of 0. This reduces the repeated pattern of initializing both APInts. Once place default constructed the APInts so I added a default constructor for those cases.

Going forward I would like to add more methods that will work on the pairs. For example trunc, zext, and sext occur on both APInts together in several places. We should probably add a clear method that can be used to clear both pieces. Maybe a method to check for conflicting information. A method to return (Zero|One) so we don't write it out everywhere. Maybe a method for (Zero|One).isAllOnesValue() to determine if all bits are known. I'm sure there are many other methods we can come up with.

Differential Revision: https://reviews.llvm.org/D32376

llvm-svn: 301432

llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 9127ddc..312d9ba 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -14,9 +14,10 @@
 #include "InstCombineInternal.h"
 #include "llvm/ADT/SetVector.h"
 #include "llvm/Analysis/ConstantFolding.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/PatternMatch.h"
-#include "llvm/Analysis/TargetLibraryInfo.h"
+#include "llvm/Support/KnownBits.h"
 using namespace llvm;
 using namespace PatternMatch;
 
@@ -676,11 +677,10 @@
         // This only works for EQ and NE
         ICI->isEquality()) {
       // If Op1C some other power of two, convert:
-      uint32_t BitWidth = Op1C->getType()->getBitWidth();
-      APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
-      computeKnownBits(ICI->getOperand(0), KnownZero, KnownOne, 0, &CI);
+      KnownBits Known(Op1C->getType()->getBitWidth());
+      computeKnownBits(ICI->getOperand(0), Known, 0, &CI);
 
-      APInt KnownZeroMask(~KnownZero);
+      APInt KnownZeroMask(~Known.Zero);
       if (KnownZeroMask.isPowerOf2()) { // Exactly 1 possible 1?
         if (!DoTransform) return ICI;
 
@@ -726,13 +726,13 @@
       Value *LHS = ICI->getOperand(0);
       Value *RHS = ICI->getOperand(1);
 
-      APInt KnownZeroLHS(BitWidth, 0), KnownOneLHS(BitWidth, 0);
-      APInt KnownZeroRHS(BitWidth, 0), KnownOneRHS(BitWidth, 0);
-      computeKnownBits(LHS, KnownZeroLHS, KnownOneLHS, 0, &CI);
-      computeKnownBits(RHS, KnownZeroRHS, KnownOneRHS, 0, &CI);
+      KnownBits KnownLHS(BitWidth);
+      KnownBits KnownRHS(BitWidth);
+      computeKnownBits(LHS, KnownLHS, 0, &CI);
+      computeKnownBits(RHS, KnownRHS, 0, &CI);
 
-      if (KnownZeroLHS == KnownZeroRHS && KnownOneLHS == KnownOneRHS) {
-        APInt KnownBits = KnownZeroLHS | KnownOneLHS;
+      if (KnownLHS.Zero == KnownRHS.Zero && KnownLHS.One == KnownRHS.One) {
+        APInt KnownBits = KnownLHS.Zero | KnownLHS.One;
         APInt UnknownBit = ~KnownBits;
         if (UnknownBit.countPopulation() == 1) {
           if (!DoTransform) return ICI;
@@ -740,7 +740,7 @@
           Value *Result = Builder->CreateXor(LHS, RHS);
 
           // Mask off any bits that are set and won't be shifted away.
-          if (KnownOneLHS.uge(UnknownBit))
+          if (KnownLHS.One.uge(UnknownBit))
             Result = Builder->CreateAnd(Result,
                                         ConstantInt::get(ITy, UnknownBit));
 
@@ -1049,10 +1049,10 @@
     if (ICI->hasOneUse() &&
         ICI->isEquality() && (Op1C->isZero() || Op1C->getValue().isPowerOf2())){
       unsigned BitWidth = Op1C->getType()->getBitWidth();
-      APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
-      computeKnownBits(Op0, KnownZero, KnownOne, 0, &CI);
+      KnownBits Known(BitWidth);
+      computeKnownBits(Op0, Known, 0, &CI);
 
-      APInt KnownZeroMask(~KnownZero);
+      APInt KnownZeroMask(~Known.Zero);
       if (KnownZeroMask.isPowerOf2()) {
         Value *In = ICI->getOperand(0);