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[InstSimplify] fold icmp based on range of abs/nabs 

This is a fix for PR39475:
https://bugs.llvm.org/show_bug.cgi?id=39475

We managed to get some of these patterns using computeKnownBits in D47041, but that 
can't be used for nabs(). Instead, put in some range-based logic, so we can fold 
both abs/nabs with icmp with a constant value.

Alive proofs:
https://rise4fun.com/Alive/21r

Name: abs_nsw_is_positive
  %cmp = icmp slt i32 %x, 0
  %negx = sub nsw i32 0, %x
  %abs = select i1 %cmp, i32 %negx, i32 %x
  %r = icmp sgt i32 %abs, -1
    =>
  %r = i1 true
 
Name: abs_nsw_is_not_negative
  %cmp = icmp slt i32 %x, 0
  %negx = sub nsw i32 0, %x
  %abs = select i1 %cmp, i32 %negx, i32 %x
  %r = icmp slt i32 %abs, 0
    =>
  %r = i1 false
 
Name: nabs_is_negative_or_0
  %cmp = icmp slt i32 %x, 0
  %negx = sub i32 0, %x
  %nabs = select i1 %cmp, i32 %x, i32 %negx
  %r = icmp slt i32 %nabs, 1
    =>
  %r = i1 true

Name: nabs_is_not_over_0
  %cmp = icmp slt i32 %x, 0
  %negx = sub i32 0, %x
  %nabs = select i1 %cmp, i32 %x, i32 %negx
  %r = icmp sgt i32 %nabs, 0
    =>
  %r = i1 false

Differential Revision: https://reviews.llvm.org/D53844

llvm-svn: 345717
This commit is contained in:
Sanjay Patel 2018-10-31 13:25:10 +00:00
parent dd2120c08f
commit 2efccd2cf2
2 changed files with 57 additions and 75 deletions
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42
llvm/lib/Analysis/InstructionSimplify.cpp
View File

@ -2996,6 +2996,45 @@ static Value *simplifyICmpWithBinOp(CmpInst::Predicate Pred, Value *LHS,
return nullptr;
}
static Value *simplifyICmpWithAbsNabs(CmpInst::Predicate Pred, Value *Op0,
Value *Op1) {
// We need a comparison with a constant.
const APInt *C;
if (!match(Op1, m_APInt(C)))
return nullptr;
// matchSelectPattern returns the negation part of an abs pattern in SP1.
// If the negate has an NSW flag, abs(INT_MIN) is undefined. Without that
// constraint, we can't make a contiguous range for the result of abs.
ICmpInst::Predicate AbsPred = ICmpInst::BAD_ICMP_PREDICATE;
Value *SP0, *SP1;
SelectPatternFlavor SPF = matchSelectPattern(Op0, SP0, SP1).Flavor;
if (SPF == SelectPatternFlavor::SPF_ABS &&
cast<Instruction>(SP1)->hasNoSignedWrap())
// The result of abs(X) is >= 0 (with nsw).
AbsPred = ICmpInst::ICMP_SGE;
if (SPF == SelectPatternFlavor::SPF_NABS)
// The result of -abs(X) is <= 0.
AbsPred = ICmpInst::ICMP_SLE;
if (AbsPred == ICmpInst::BAD_ICMP_PREDICATE)
return nullptr;
// Intersect the range of abs/nabs with the range of this icmp.
// If there is no intersection, the icmp must be false.
// If the intersection equals the range of abs/nabs, the icmp must be true.
APInt Zero = APInt::getNullValue(C->getBitWidth());
ConstantRange AbsRange = ConstantRange::makeExactICmpRegion(AbsPred, Zero);
ConstantRange CmpRange = ConstantRange::makeExactICmpRegion(Pred, *C);
ConstantRange Intersection = AbsRange.intersectWith(CmpRange);
if (Intersection.isEmptySet())
return getFalse(GetCompareTy(Op0));
if (Intersection == AbsRange)
return getTrue(GetCompareTy(Op0));
return nullptr;
}
/// Simplify integer comparisons where at least one operand of the compare
/// matches an integer min/max idiom.
static Value *simplifyICmpWithMinMax(CmpInst::Predicate Pred, Value *LHS,
@ -3427,6 +3466,9 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
if (Value *V = simplifyICmpWithMinMax(Pred, LHS, RHS, Q, MaxRecurse))
return V;
if (Value *V = simplifyICmpWithAbsNabs(Pred, LHS, RHS))
return V;
// Simplify comparisons of related pointers using a powerful, recursive
// GEP-walk when we have target data available..
if (LHS->getType()->isPointerTy())

90
llvm/test/Transforms/InstSimplify/icmp-abs-nabs.ll
View File

@ -5,11 +5,7 @@
define i1 @abs_nsw_is_positive(i32 %x) {
; CHECK-LABEL: @abs_nsw_is_positive(
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i32 [[X:%.*]], 0
; CHECK-NEXT: [[NEGX:%.*]] = sub nsw i32 0, [[X]]
; CHECK-NEXT: [[ABS:%.*]] = select i1 [[CMP]], i32 [[NEGX]], i32 [[X]]
; CHECK-NEXT: [[R:%.*]] = icmp sgt i32 [[ABS]], -1
; CHECK-NEXT: ret i1 [[R]]
; CHECK-NEXT: ret i1 true
;
%cmp = icmp slt i32 %x, 0
%negx = sub nsw i32 0, %x
@ -35,11 +31,7 @@ define i1 @abs_nsw_is_positive_sge(i32 %x) {
define i1 @abs_nsw_is_positive_reduced_range(i32 %x) {
; CHECK-LABEL: @abs_nsw_is_positive_reduced_range(
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i32 [[X:%.*]], 0
; CHECK-NEXT: [[NEGX:%.*]] = sub nsw i32 0, [[X]]
; CHECK-NEXT: [[ABS:%.*]] = select i1 [[CMP]], i32 [[NEGX]], i32 [[X]]
; CHECK-NEXT: [[R:%.*]] = icmp sgt i32 [[ABS]], -42
; CHECK-NEXT: ret i1 [[R]]
; CHECK-NEXT: ret i1 true
;
%cmp = icmp slt i32 %x, 0
%negx = sub nsw i32 0, %x
@ -99,11 +91,7 @@ define i1 @abs_nsw_is_not_negative(i32 %x) {
define i1 @abs_nsw_is_not_negative_sle(i32 %x) {
; CHECK-LABEL: @abs_nsw_is_not_negative_sle(
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i32 [[X:%.*]], 1
; CHECK-NEXT: [[NEGX:%.*]] = sub nsw i32 0, [[X]]
; CHECK-NEXT: [[ABS:%.*]] = select i1 [[CMP]], i32 [[NEGX]], i32 [[X]]
; CHECK-NEXT: [[R:%.*]] = icmp sle i32 [[ABS]], -1
; CHECK-NEXT: ret i1 [[R]]
; CHECK-NEXT: ret i1 false
;
%cmp = icmp slt i32 %x, 1
%negx = sub nsw i32 0, %x
@ -116,11 +104,7 @@ define i1 @abs_nsw_is_not_negative_sle(i32 %x) {
define i1 @abs_nsw_is_not_negative_reduced_range(i32 %x) {
; CHECK-LABEL: @abs_nsw_is_not_negative_reduced_range(
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i32 [[X:%.*]], 0
; CHECK-NEXT: [[NEGX:%.*]] = sub nsw i32 0, [[X]]
; CHECK-NEXT: [[ABS:%.*]] = select i1 [[CMP]], i32 [[NEGX]], i32 [[X]]
; CHECK-NEXT: [[R:%.*]] = icmp slt i32 [[ABS]], -24
; CHECK-NEXT: ret i1 [[R]]
; CHECK-NEXT: ret i1 false
;
%cmp = icmp slt i32 %x, 0
%negx = sub nsw i32 0, %x
@ -167,11 +151,7 @@ define i1 @abs_nsw_is_not_negative_wrong_range(i32 %x) {
define i1 @nabs_is_negative_or_0(i32 %x) {
; CHECK-LABEL: @nabs_is_negative_or_0(
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i32 [[X:%.*]], 0
; CHECK-NEXT: [[NEGX:%.*]] = sub i32 0, [[X]]
; CHECK-NEXT: [[NABS:%.*]] = select i1 [[CMP]], i32 [[X]], i32 [[NEGX]]
; CHECK-NEXT: [[R:%.*]] = icmp slt i32 [[NABS]], 1
; CHECK-NEXT: ret i1 [[R]]
; CHECK-NEXT: ret i1 true
;
%cmp = icmp slt i32 %x, 0
%negx = sub i32 0, %x
@ -184,11 +164,7 @@ define i1 @nabs_is_negative_or_0(i32 %x) {
define i1 @nabs_is_negative_or_0_sle(i32 %x) {
; CHECK-LABEL: @nabs_is_negative_or_0_sle(
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i32 [[X:%.*]], 1
; CHECK-NEXT: [[NEGX:%.*]] = sub i32 0, [[X]]
; CHECK-NEXT: [[NABS:%.*]] = select i1 [[CMP]], i32 [[X]], i32 [[NEGX]]
; CHECK-NEXT: [[R:%.*]] = icmp sle i32 [[NABS]], 0
; CHECK-NEXT: ret i1 [[R]]
; CHECK-NEXT: ret i1 true
;
%cmp = icmp slt i32 %x, 1
%negx = sub i32 0, %x
@ -201,11 +177,7 @@ define i1 @nabs_is_negative_or_0_sle(i32 %x) {
define i1 @nabs_is_negative_or_0_reduced_range(i32 %x) {
; CHECK-LABEL: @nabs_is_negative_or_0_reduced_range(
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i32 [[X:%.*]], 1
; CHECK-NEXT: [[NEGX:%.*]] = sub i32 0, [[X]]
; CHECK-NEXT: [[NABS:%.*]] = select i1 [[CMP]], i32 [[X]], i32 [[NEGX]]
; CHECK-NEXT: [[R:%.*]] = icmp slt i32 [[NABS]], 421
; CHECK-NEXT: ret i1 [[R]]
; CHECK-NEXT: ret i1 true
;
%cmp = icmp slt i32 %x, 1
%negx = sub i32 0, %x
@ -235,11 +207,7 @@ define i1 @nabs_is_negative_or_0_wrong_range(i32 %x) {
define i1 @nabs_is_not_over_0(i32 %x) {
; CHECK-LABEL: @nabs_is_not_over_0(
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i32 [[X:%.*]], 0
; CHECK-NEXT: [[NEGX:%.*]] = sub i32 0, [[X]]
; CHECK-NEXT: [[NABS:%.*]] = select i1 [[CMP]], i32 [[X]], i32 [[NEGX]]
; CHECK-NEXT: [[R:%.*]] = icmp sgt i32 [[NABS]], 0
; CHECK-NEXT: ret i1 [[R]]
; CHECK-NEXT: ret i1 false
;
%cmp = icmp slt i32 %x, 0
%negx = sub i32 0, %x
@ -252,11 +220,7 @@ define i1 @nabs_is_not_over_0(i32 %x) {
define i1 @nabs_is_not_over_0_sle(i32 %x) {
; CHECK-LABEL: @nabs_is_not_over_0_sle(
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i32 [[X:%.*]], 1
; CHECK-NEXT: [[NEGX:%.*]] = sub i32 0, [[X]]
; CHECK-NEXT: [[NABS:%.*]] = select i1 [[CMP]], i32 [[X]], i32 [[NEGX]]
; CHECK-NEXT: [[R:%.*]] = icmp sge i32 [[NABS]], 1
; CHECK-NEXT: ret i1 [[R]]
; CHECK-NEXT: ret i1 false
;
%cmp = icmp slt i32 %x, 1
%negx = sub i32 0, %x
@ -269,11 +233,7 @@ define i1 @nabs_is_not_over_0_sle(i32 %x) {
define i1 @nabs_is_not_over_0_reduced_range(i32 %x) {
; CHECK-LABEL: @nabs_is_not_over_0_reduced_range(
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i32 [[X:%.*]], 1
; CHECK-NEXT: [[NEGX:%.*]] = sub i32 0, [[X]]
; CHECK-NEXT: [[NABS:%.*]] = select i1 [[CMP]], i32 [[X]], i32 [[NEGX]]
; CHECK-NEXT: [[R:%.*]] = icmp sgt i32 [[NABS]], 4223
; CHECK-NEXT: ret i1 [[R]]
; CHECK-NEXT: ret i1 false
;
%cmp = icmp slt i32 %x, 1
%negx = sub i32 0, %x
@ -318,11 +278,7 @@ define i1 @abs_nsw_is_positive_eq(i32 %x) {
define i1 @abs_nsw_is_positive_ult(i8 %x) {
; CHECK-LABEL: @abs_nsw_is_positive_ult(
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i8 [[X:%.*]], 0
; CHECK-NEXT: [[NEGX:%.*]] = sub nsw i8 0, [[X]]
; CHECK-NEXT: [[ABS:%.*]] = select i1 [[CMP]], i8 [[NEGX]], i8 [[X]]
; CHECK-NEXT: [[R:%.*]] = icmp ult i8 [[ABS]], -117
; CHECK-NEXT: ret i1 [[R]]
; CHECK-NEXT: ret i1 true
;
%cmp = icmp slt i8 %x, 0
%negx = sub nsw i8 0, %x
@ -335,11 +291,7 @@ define i1 @abs_nsw_is_positive_ult(i8 %x) {
define i1 @abs_nsw_is_not_negative_ugt(i8 %x) {
; CHECK-LABEL: @abs_nsw_is_not_negative_ugt(
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i8 [[X:%.*]], 0
; CHECK-NEXT: [[NEGX:%.*]] = sub nsw i8 0, [[X]]
; CHECK-NEXT: [[ABS:%.*]] = select i1 [[CMP]], i8 [[NEGX]], i8 [[X]]
; CHECK-NEXT: [[R:%.*]] = icmp ugt i8 [[ABS]], 127
; CHECK-NEXT: ret i1 [[R]]
; CHECK-NEXT: ret i1 false
;
%cmp = icmp slt i8 %x, 0
%negx = sub nsw i8 0, %x
@ -352,11 +304,7 @@ define i1 @abs_nsw_is_not_negative_ugt(i8 %x) {
define <2 x i1> @abs_nsw_is_not_negative_vec_splat(<2 x i32> %x) {
; CHECK-LABEL: @abs_nsw_is_not_negative_vec_splat(
; CHECK-NEXT: [[CMP:%.*]] = icmp slt <2 x i32> [[X:%.*]], zeroinitializer
; CHECK-NEXT: [[NEGX:%.*]] = sub nsw <2 x i32> zeroinitializer, [[X]]
; CHECK-NEXT: [[ABS:%.*]] = select <2 x i1> [[CMP]], <2 x i32> [[NEGX]], <2 x i32> [[X]]
; CHECK-NEXT: [[R:%.*]] = icmp slt <2 x i32> [[ABS]], <i32 -8, i32 -8>
; CHECK-NEXT: ret <2 x i1> [[R]]
; CHECK-NEXT: ret <2 x i1> zeroinitializer
;
%cmp = icmp slt <2 x i32> %x, zeroinitializer
%negx = sub nsw <2 x i32> zeroinitializer, %x
@ -369,11 +317,7 @@ define <2 x i1> @abs_nsw_is_not_negative_vec_splat(<2 x i32> %x) {
define i1 @nabs_is_negative_or_0_ne(i8 %x) {
; CHECK-LABEL: @nabs_is_negative_or_0_ne(
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i8 [[X:%.*]], 0
; CHECK-NEXT: [[NEGX:%.*]] = sub i8 0, [[X]]
; CHECK-NEXT: [[NABS:%.*]] = select i1 [[CMP]], i8 [[X]], i8 [[NEGX]]
; CHECK-NEXT: [[R:%.*]] = icmp ne i8 [[NABS]], 12
; CHECK-NEXT: ret i1 [[R]]
; CHECK-NEXT: ret i1 true
;
%cmp = icmp slt i8 %x, 0
%negx = sub i8 0, %x
@ -386,11 +330,7 @@ define i1 @nabs_is_negative_or_0_ne(i8 %x) {
define <3 x i1> @nabs_is_not_over_0_sle_vec_splat(<3 x i33> %x) {
; CHECK-LABEL: @nabs_is_not_over_0_sle_vec_splat(
; CHECK-NEXT: [[CMP:%.*]] = icmp slt <3 x i33> [[X:%.*]], <i33 1, i33 1, i33 1>
; CHECK-NEXT: [[NEGX:%.*]] = sub <3 x i33> zeroinitializer, [[X]]
; CHECK-NEXT: [[NABS:%.*]] = select <3 x i1> [[CMP]], <3 x i33> [[X]], <3 x i33> [[NEGX]]
; CHECK-NEXT: [[R:%.*]] = icmp sge <3 x i33> [[NABS]], <i33 1, i33 1, i33 1>
; CHECK-NEXT: ret <3 x i1> [[R]]
; CHECK-NEXT: ret <3 x i1> zeroinitializer
;
%cmp = icmp slt <3 x i33> %x, <i33 1, i33 1, i33 1>
%negx = sub <3 x i33> zeroinitializer, %x