[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
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 1cc0554..3ac4bf1 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -89,6 +89,7 @@
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/KnownBits.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Support/SaveAndRestore.h"
@@ -4575,10 +4576,10 @@
if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(S)) {
// For a SCEVUnknown, ask ValueTracking.
unsigned BitWidth = getTypeSizeInBits(U->getType());
- APInt Zeros(BitWidth, 0), Ones(BitWidth, 0);
- computeKnownBits(U->getValue(), Zeros, Ones, getDataLayout(), 0, &AC,
+ KnownBits Known(BitWidth);
+ computeKnownBits(U->getValue(), Known, getDataLayout(), 0, &AC,
nullptr, &DT);
- return Zeros.countTrailingOnes();
+ return Known.Zero.countTrailingOnes();
}
// SCEVUDivExpr
@@ -4757,11 +4758,12 @@
const DataLayout &DL = getDataLayout();
if (SignHint == ScalarEvolution::HINT_RANGE_UNSIGNED) {
// For a SCEVUnknown, ask ValueTracking.
- APInt Zeros(BitWidth, 0), Ones(BitWidth, 0);
- computeKnownBits(U->getValue(), Zeros, Ones, DL, 0, &AC, nullptr, &DT);
- if (Ones != ~Zeros + 1)
+ KnownBits Known(BitWidth);
+ computeKnownBits(U->getValue(), Known, DL, 0, &AC, nullptr, &DT);
+ if (Known.One != ~Known.Zero + 1)
ConservativeResult =
- ConservativeResult.intersectWith(ConstantRange(Ones, ~Zeros + 1));
+ ConservativeResult.intersectWith(ConstantRange(Known.One,
+ ~Known.Zero + 1));
} else {
assert(SignHint == ScalarEvolution::HINT_RANGE_SIGNED &&
"generalize as needed!");
@@ -5292,13 +5294,13 @@
unsigned LZ = A.countLeadingZeros();
unsigned TZ = A.countTrailingZeros();
unsigned BitWidth = A.getBitWidth();
- APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
- computeKnownBits(BO->LHS, KnownZero, KnownOne, getDataLayout(),
+ KnownBits Known(BitWidth);
+ computeKnownBits(BO->LHS, Known, getDataLayout(),
0, &AC, nullptr, &DT);
APInt EffectiveMask =
APInt::getLowBitsSet(BitWidth, BitWidth - LZ - TZ).shl(TZ);
- if ((LZ != 0 || TZ != 0) && !((~A & ~KnownZero) & EffectiveMask)) {
+ if ((LZ != 0 || TZ != 0) && !((~A & ~Known.Zero) & EffectiveMask)) {
const SCEV *MulCount = getConstant(APInt::getOneBitSet(BitWidth, TZ));
const SCEV *LHS = getSCEV(BO->LHS);
const SCEV *ShiftedLHS = nullptr;