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[ValueTracking] An improvement to IR ValueTracking on Non-negative Integers

Since this change is known to cause performance degradations in some cases it's commited under a temporary flag which is turned off by default.

Patch by Li Huang

Differential Revision: https://reviews.llvm.org/D18777

llvm-svn: 284022
This commit is contained in:
Artur Pilipenko 2016-10-12 16:18:43 +00:00
parent f80a9a7346
commit 6245b73221
2 changed files with 48 additions and 5 deletions

View File

@ -51,6 +51,12 @@ const unsigned MaxDepth = 6;
static cl::opt<unsigned> DomConditionsMaxUses("dom-conditions-max-uses",
cl::Hidden, cl::init(20));
// This optimization is known to cause performance regressions is some cases,
// keep it under a temporary flag for now.
static cl::opt<bool>
DontImproveNonNegativePhiBits("dont-improve-non-negative-phi-bits",
cl::Hidden, cl::init(true));
/// Returns the bitwidth of the given scalar or pointer type (if unknown returns
/// 0). For vector types, returns the element type's bitwidth.
static unsigned getBitWidth(Type *Ty, const DataLayout &DL) {
@ -1300,9 +1306,46 @@ static void computeKnownBitsFromOperator(const Operator *I, APInt &KnownZero,
APInt KnownZero3(KnownZero), KnownOne3(KnownOne);
computeKnownBits(L, KnownZero3, KnownOne3, Depth + 1, Q);
KnownZero = APInt::getLowBitsSet(BitWidth,
std::min(KnownZero2.countTrailingOnes(),
KnownZero3.countTrailingOnes()));
KnownZero = APInt::getLowBitsSet(
BitWidth, std::min(KnownZero2.countTrailingOnes(),
KnownZero3.countTrailingOnes()));
if (DontImproveNonNegativePhiBits)
break;
auto *OverflowOp = dyn_cast<OverflowingBinaryOperator>(LU);
if (OverflowOp && OverflowOp->hasNoSignedWrap()) {
// If initial value of recurrence is nonnegative, and we are adding
// a nonnegative number with nsw, the result can only be nonnegative
// or poison value regardless of the number of times we execute the
// add in phi recurrence. If initial value is negative and we are
// adding a negative number with nsw, the result can only be
// negative or poison value. Similar arguments apply to sub and mul.
//
// (add non-negative, non-negative) --> non-negative
// (add negative, negative) --> negative
if (Opcode == Instruction::Add) {
if (KnownZero2.isNegative() && KnownZero3.isNegative())
KnownZero.setBit(BitWidth - 1);
else if (KnownOne2.isNegative() && KnownOne3.isNegative())
KnownOne.setBit(BitWidth - 1);
}
// (sub nsw non-negative, negative) --> non-negative
// (sub nsw negative, non-negative) --> negative
else if (Opcode == Instruction::Sub && LL == I) {
if (KnownZero2.isNegative() && KnownOne3.isNegative())
KnownZero.setBit(BitWidth - 1);
else if (KnownOne2.isNegative() && KnownZero3.isNegative())
KnownOne.setBit(BitWidth - 1);
}
// (mul nsw non-negative, non-negative) --> non-negative
else if (Opcode == Instruction::Mul && KnownZero2.isNegative() &&
KnownZero3.isNegative())
KnownZero.setBit(BitWidth - 1);
}
break;
}
}

View File

@ -1,7 +1,7 @@
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
; RUN: opt < %s -bb-vectorize -bb-vectorize-req-chain-depth=3 -bb-vectorize-ignore-target-info -instcombine -gvn -S | FileCheck %s
; RUN: opt < %s -basicaa -loop-unroll -unroll-threshold=45 -unroll-allow-partial -bb-vectorize -bb-vectorize-req-chain-depth=3 -bb-vectorize-ignore-target-info -instcombine -gvn -S | FileCheck %s -check-prefix=CHECK-UNRL
; RUN: opt < %s -dont-improve-non-negative-phi-bits=false -basicaa -loop-unroll -unroll-threshold=45 -unroll-allow-partial -bb-vectorize -bb-vectorize-req-chain-depth=3 -bb-vectorize-ignore-target-info -instcombine -gvn -S | FileCheck %s -check-prefix=CHECK-UNRL
; The second check covers the use of alias analysis (with loop unrolling).
define void @test1(double* noalias %out, double* noalias %in1, double* noalias %in2) nounwind uwtable {
@ -83,7 +83,7 @@ for.body: ; preds = %for.body, %entry
; CHECK-UNRL: %add12 = fadd <2 x double> %add7, %mul11
; CHECK-UNRL: %4 = bitcast double* %arrayidx14 to <2 x double>*
; CHECK-UNRL: store <2 x double> %add12, <2 x double>* %4, align 8
; CHECK-UNRL: %indvars.iv.next.1 = add nsw i64 %indvars.iv, 2
; CHECK-UNRL: %indvars.iv.next.1 = add nuw nsw i64 %indvars.iv, 2
; CHECK-UNRL: %lftr.wideiv.1 = trunc i64 %indvars.iv.next.1 to i32
; CHECK-UNRL: %exitcond.1 = icmp eq i32 %lftr.wideiv.1, 10
; CHECK-UNRL: br i1 %exitcond.1, label %for.end, label %for.body