[llvm] r310378 - [KnownBits][ValueTracking] Move the math for calculating known bits for add/sub into a static method in KnownBits object
Craig Topper via llvm-commits
llvm-commits at lists.llvm.org
Tue Aug 8 09:29:35 PDT 2017
Author: ctopper
Date: Tue Aug 8 09:29:35 2017
New Revision: 310378
URL: http://llvm.org/viewvc/llvm-project?rev=310378&view=rev
Log:
[KnownBits][ValueTracking] Move the math for calculating known bits for add/sub into a static method in KnownBits object
I want to reuse this code in SimplifyDemandedBits handling of Add/Sub. This will make that easier.
Wonder if we should use it in SelectionDAG's computeKnownBits too.
Differential Revision: https://reviews.llvm.org/D36433
Added:
llvm/trunk/lib/Support/KnownBits.cpp (with props)
Modified:
llvm/trunk/include/llvm/Support/KnownBits.h
llvm/trunk/lib/Analysis/ValueTracking.cpp
llvm/trunk/lib/Support/CMakeLists.txt
Modified: llvm/trunk/include/llvm/Support/KnownBits.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/KnownBits.h?rev=310378&r1=310377&r2=310378&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Support/KnownBits.h (original)
+++ llvm/trunk/include/llvm/Support/KnownBits.h Tue Aug 8 09:29:35 2017
@@ -193,6 +193,10 @@ public:
unsigned countMaxPopulation() const {
return getBitWidth() - Zero.countPopulation();
}
+
+ /// Compute known bits resulting from adding LHS and RHS.
+ static KnownBits computeForAddSub(bool Add, bool NSW, const KnownBits &LHS,
+ KnownBits RHS);
};
} // end namespace llvm
Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=310378&r1=310377&r2=310378&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp Tue Aug 8 09:29:35 2017
@@ -275,47 +275,7 @@ static void computeKnownBitsAddSub(bool
computeKnownBits(Op0, LHSKnown, Depth + 1, Q);
computeKnownBits(Op1, Known2, Depth + 1, Q);
- // Carry in a 1 for a subtract, rather than a 0.
- uint64_t CarryIn = 0;
- if (!Add) {
- // Sum = LHS + ~RHS + 1
- std::swap(Known2.Zero, Known2.One);
- CarryIn = 1;
- }
-
- APInt PossibleSumZero = ~LHSKnown.Zero + ~Known2.Zero + CarryIn;
- APInt PossibleSumOne = LHSKnown.One + Known2.One + CarryIn;
-
- // Compute known bits of the carry.
- APInt CarryKnownZero = ~(PossibleSumZero ^ LHSKnown.Zero ^ Known2.Zero);
- APInt CarryKnownOne = PossibleSumOne ^ LHSKnown.One ^ Known2.One;
-
- // Compute set of known bits (where all three relevant bits are known).
- APInt LHSKnownUnion = LHSKnown.Zero | LHSKnown.One;
- APInt RHSKnownUnion = Known2.Zero | Known2.One;
- APInt CarryKnownUnion = CarryKnownZero | CarryKnownOne;
- APInt Known = LHSKnownUnion & RHSKnownUnion & CarryKnownUnion;
-
- assert((PossibleSumZero & Known) == (PossibleSumOne & Known) &&
- "known bits of sum differ");
-
- // Compute known bits of the result.
- KnownOut.Zero = ~PossibleSumOne & Known;
- KnownOut.One = PossibleSumOne & Known;
-
- // Are we still trying to solve for the sign bit?
- if (!Known.isSignBitSet()) {
- if (NSW) {
- // Adding two non-negative numbers, or subtracting a negative number from
- // a non-negative one, can't wrap into negative.
- if (LHSKnown.isNonNegative() && Known2.isNonNegative())
- KnownOut.makeNonNegative();
- // Adding two negative numbers, or subtracting a non-negative number from
- // a negative one, can't wrap into non-negative.
- else if (LHSKnown.isNegative() && Known2.isNegative())
- KnownOut.makeNegative();
- }
- }
+ KnownOut = KnownBits::computeForAddSub(Add, NSW, LHSKnown, Known2);
}
static void computeKnownBitsMul(const Value *Op0, const Value *Op1, bool NSW,
Modified: llvm/trunk/lib/Support/CMakeLists.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/CMakeLists.txt?rev=310378&r1=310377&r2=310378&view=diff
==============================================================================
--- llvm/trunk/lib/Support/CMakeLists.txt (original)
+++ llvm/trunk/lib/Support/CMakeLists.txt Tue Aug 8 09:29:35 2017
@@ -71,6 +71,7 @@ add_llvm_library(LLVMSupport
IntEqClasses.cpp
IntervalMap.cpp
JamCRC.cpp
+ KnownBits.cpp
LEB128.cpp
LineIterator.cpp
Locale.cpp
Added: llvm/trunk/lib/Support/KnownBits.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/KnownBits.cpp?rev=310378&view=auto
==============================================================================
--- llvm/trunk/lib/Support/KnownBits.cpp (added)
+++ llvm/trunk/lib/Support/KnownBits.cpp Tue Aug 8 09:29:35 2017
@@ -0,0 +1,65 @@
+//===-- KnownBits.cpp - Stores known zeros/ones ---------------------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains a class for representing known zeros and ones used by
+// computeKnownBits.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/KnownBits.h"
+
+using namespace llvm;
+
+KnownBits KnownBits::computeForAddSub(bool Add, bool NSW,
+ const KnownBits &LHS, KnownBits RHS) {
+ // Carry in a 1 for a subtract, rather than 0.
+ bool CarryIn = false;
+ if (!Add) {
+ // Sum = LHS + ~RHS + 1
+ std::swap(RHS.Zero, RHS.One);
+ CarryIn = true;
+ }
+
+ APInt PossibleSumZero = ~LHS.Zero + ~RHS.Zero + CarryIn;
+ APInt PossibleSumOne = LHS.One + RHS.One + CarryIn;
+
+ // Compute known bits of the carry.
+ APInt CarryKnownZero = ~(PossibleSumZero ^ LHS.Zero ^ RHS.Zero);
+ APInt CarryKnownOne = PossibleSumOne ^ LHS.One ^ RHS.One;
+
+ // Compute set of known bits (where all three relevant bits are known).
+ APInt LHSKnownUnion = LHS.Zero | LHS.One;
+ APInt RHSKnownUnion = RHS.Zero | RHS.One;
+ APInt CarryKnownUnion = std::move(CarryKnownZero) | CarryKnownOne;
+ APInt Known = std::move(LHSKnownUnion) & RHSKnownUnion & CarryKnownUnion;
+
+ assert((PossibleSumZero & Known) == (PossibleSumOne & Known) &&
+ "known bits of sum differ");
+
+ // Compute known bits of the result.
+ KnownBits KnownOut;
+ KnownOut.Zero = ~std::move(PossibleSumZero) & Known;
+ KnownOut.One = std::move(PossibleSumOne) & Known;
+
+ // Are we still trying to solve for the sign bit?
+ if (!Known.isSignBitSet()) {
+ if (NSW) {
+ // Adding two non-negative numbers, or subtracting a negative number from
+ // a non-negative one, can't wrap into negative.
+ if (LHS.isNonNegative() && RHS.isNonNegative())
+ KnownOut.makeNonNegative();
+ // Adding two negative numbers, or subtracting a non-negative number from
+ // a negative one, can't wrap into non-negative.
+ else if (LHS.isNegative() && RHS.isNegative())
+ KnownOut.makeNegative();
+ }
+ }
+
+ return KnownOut;
+}
Propchange: llvm/trunk/lib/Support/KnownBits.cpp
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Propchange: llvm/trunk/lib/Support/KnownBits.cpp
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