[llvm] r284022 - [ValueTracking] An improvement to IR ValueTracking on Non-negative Integers
Artur Pilipenko via llvm-commits
llvm-commits at lists.llvm.org
Wed Oct 12 09:18:43 PDT 2016
Author: apilipenko
Date: Wed Oct 12 11:18:43 2016
New Revision: 284022
URL: http://llvm.org/viewvc/llvm-project?rev=284022&view=rev
Log:
[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
Modified:
llvm/trunk/lib/Analysis/ValueTracking.cpp
llvm/trunk/test/Transforms/BBVectorize/loop1.ll
Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=284022&r1=284021&r2=284022&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp Wed Oct 12 11:18:43 2016
@@ -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
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;
}
}
Modified: llvm/trunk/test/Transforms/BBVectorize/loop1.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/BBVectorize/loop1.ll?rev=284022&r1=284021&r2=284022&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/BBVectorize/loop1.ll (original)
+++ llvm/trunk/test/Transforms/BBVectorize/loop1.ll Wed Oct 12 11:18:43 2016
@@ -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:
; 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
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