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

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Patch by Li Huang

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

llvm-svn: 278267
This commit is contained in:
Andrew Kaylor 2016-08-10 18:47:19 +00:00
parent 8197d268d7
commit 6c20f4ff06
3 changed files with 135 additions and 2 deletions
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38
lib/Analysis/ValueTracking.cpp
View File

@ -1272,7 +1272,9 @@ static void computeKnownBitsFromOperator(Operator *I, APInt &KnownZero,
unsigned Opcode = LU->getOpcode();
// Check for operations that have the property that if
// both their operands have low zero bits, the result
// will have low zero bits.
// will have low zero bits. Also check for operations
// that are known to produce non-negative or negative
// recurrence values.
if (Opcode == Instruction::Add ||
Opcode == Instruction::Sub ||
Opcode == Instruction::And ||
@ -1298,6 +1300,40 @@ static void computeKnownBitsFromOperator(Operator *I, APInt &KnownZero,
KnownZero = APInt::getLowBitsSet(BitWidth,
std::min(KnownZero2.countTrailingOnes(),
KnownZero3.countTrailingOnes()));
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;
}
}

97
test/Analysis/ValueTracking/iv-known-sign.ll Normal file
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@ -0,0 +1,97 @@
; RUN: opt < %s -instcombine -S | FileCheck %s
; Induction variable is known to be non-negative
; when its initial value is non-negative and
; increments by non-negative value
define i32 @test_indvar_nonnegative_add() {
; CHECK-LABEL: @test_indvar_nonnegative_add(
; CHECK: br i1 true, label %for.end, label %for.body
entry:
br label %for.body
for.body:
%i = phi i32 [0, %entry], [%inc, %for.body]
%inc = add nsw i32 %i, 1
%cmp = icmp sge i32 %i, 0
br i1 %cmp, label %for.end, label %for.body
for.end:
ret i32 %i
}
; Induction variable is known to be non-negative
; when its initial value is non-negative and
; is multiplied by a non-negative value in each
; iteration
define i32 @test_indvar_nonnegative_mul() {
; CHECK-LABEL: @test_indvar_nonnegative_mul(
; CHECK: br i1 true, label %for.end, label %for.body
entry:
br label %for.body
for.body:
%i = phi i32 [1, %entry], [%inc, %for.body]
%inc = mul nsw i32 %i, 3
%cmp = icmp sge i32 %i, 0
br i1 %cmp, label %for.end, label %for.body
for.end:
ret i32 %i
}
; Induction variable is known to be non-negative,
; Similar to add
define i32 @test_indvar_nonnegative_sub(i32 %a) {
; CHECK-LABEL: @test_indvar_nonnegative_sub(
; CHECK: br i1 true, label %for.end, label %for.body
entry:
br label %for.body
for.body:
%i = phi i32 [0, %entry], [%inc, %for.body]
%b = or i32 %a, -2147483648
%inc = sub nsw i32 %i, %b
%cmp = icmp sge i32 %i, 0
br i1 %cmp, label %for.end, label %for.body
for.end:
ret i32 %i
}
; Induction variable is known to be negative when
; its initial value is negative and decrements by
; a non-negative value
define i32 @test_indvar_negative_add() {
; CHECK-LABEL: @test_indvar_negative_add(
; CHECK: br i1 true, label %for.end, label %for.body
entry:
br label %for.body
for.body:
%i = phi i32 [-1, %entry], [%inc, %for.body]
%inc = add nsw i32 %i, -1
%cmp = icmp slt i32 %i, 0
br i1 %cmp, label %for.end, label %for.body
for.end:
ret i32 %i
}
; Induction variable is known to be negative,
; similar to add
define i32 @test_indvar_negative_sub(i32 %a) {
; CHECK-LABEL: @test_indvar_negative_sub(
; CHECK: br i1 true, label %for.end, label %for.body
entry:
br label %for.body
for.body:
%i = phi i32 [-1, %entry], [%inc, %for.body]
%b = and i32 %a, 2147483647
%inc = sub nsw i32 %i, %b
%cmp = icmp slt i32 %i, 0
br i1 %cmp, label %for.end, label %for.body
for.end:
ret i32 %i
}

2
test/Transforms/BBVectorize/loop1.ll
View File

@ -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