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[InstCombine] Combine no-wrap sub and icmp w/ constant. 

Teach InstCombine the transformation `(icmp P (sub nuw|nsw C2, Y), C) -> (icmp swap(P) Y, C2-C)`

Reviewers: majnemer, apilipenko, sanjoy, spatel, lebedev.ri

Reviewed By: lebedev.ri

Subscribers: dmgreen, lebedev.ri, nikic, hiraditya, JDevlieghere, jfb, jdoerfert, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D59916

llvm-svn: 357674
This commit is contained in:
Luqman Aden 2019-04-04 07:08:30 +00:00
parent 3649c20884
commit 8911c5be46
2 changed files with 14 additions and 9 deletions
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11
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -2321,6 +2321,16 @@ Instruction *InstCombiner::foldICmpSubConstant(ICmpInst &Cmp,
const APInt &C) {
Value *X = Sub->getOperand(0), *Y = Sub->getOperand(1);
ICmpInst::Predicate Pred = Cmp.getPredicate();
const APInt *C2;
APInt SubResult;
// (icmp P (sub nuw|nsw C2, Y), C) -> (icmp swap(P) Y, C2-C)
if (match(X, m_APInt(C2)) &&
((Cmp.isUnsigned() && Sub->hasNoUnsignedWrap()) ||
(Cmp.isSigned() && Sub->hasNoSignedWrap())) &&
!subWithOverflow(SubResult, *C2, C, Cmp.isSigned()))
return new ICmpInst(Cmp.getSwappedPredicate(), Y,
ConstantInt::get(Y->getType(), SubResult));
// The following transforms are only worth it if the only user of the subtract
// is the icmp.
@ -2345,7 +2355,6 @@ Instruction *InstCombiner::foldICmpSubConstant(ICmpInst &Cmp,
return new ICmpInst(ICmpInst::ICMP_SLE, X, Y);
}
const APInt *C2;
if (!match(X, m_APInt(C2)))
return nullptr;

12
llvm/test/Transforms/InstCombine/icmp-sub.ll
View File

@ -3,8 +3,7 @@
define i1 @test_nuw_and_unsigned_pred(i64 %x) {
; CHECK-LABEL: @test_nuw_and_unsigned_pred(
; CHECK-NEXT: [[Y:%.*]] = sub nuw i64 10, [[X:%.*]]
; CHECK-NEXT: [[Z:%.*]] = icmp ult i64 [[Y]], 3
; CHECK-NEXT: [[Z:%.*]] = icmp ugt i64 [[X:%.*]], 7
; CHECK-NEXT: ret i1 [[Z]]
;
%y = sub nuw i64 10, %x
@ -14,8 +13,7 @@ define i1 @test_nuw_and_unsigned_pred(i64 %x) {
define i1 @test_nsw_and_signed_pred(i64 %x) {
; CHECK-LABEL: @test_nsw_and_signed_pred(
; CHECK-NEXT: [[Y:%.*]] = sub nsw i64 3, [[X:%.*]]
; CHECK-NEXT: [[Z:%.*]] = icmp sgt i64 [[Y]], 10
; CHECK-NEXT: [[Z:%.*]] = icmp slt i64 [[X:%.*]], -7
; CHECK-NEXT: ret i1 [[Z]]
;
%y = sub nsw i64 3, %x
@ -25,8 +23,7 @@ define i1 @test_nsw_and_signed_pred(i64 %x) {
define i1 @test_nuw_nsw_and_unsigned_pred(i64 %x) {
; CHECK-LABEL: @test_nuw_nsw_and_unsigned_pred(
; CHECK-NEXT: [[Y:%.*]] = sub nuw nsw i64 10, [[X:%.*]]
; CHECK-NEXT: [[Z:%.*]] = icmp ult i64 [[Y]], 4
; CHECK-NEXT: [[Z:%.*]] = icmp ugt i64 [[X:%.*]], 6
; CHECK-NEXT: ret i1 [[Z]]
;
%y = sub nuw nsw i64 10, %x
@ -36,8 +33,7 @@ define i1 @test_nuw_nsw_and_unsigned_pred(i64 %x) {
define i1 @test_nuw_nsw_and_signed_pred(i64 %x) {
; CHECK-LABEL: @test_nuw_nsw_and_signed_pred(
; CHECK-NEXT: [[Y:%.*]] = sub nuw nsw i64 10, [[X:%.*]]
; CHECK-NEXT: [[Z:%.*]] = icmp slt i64 [[Y]], 3
; CHECK-NEXT: [[Z:%.*]] = icmp sgt i64 [[X:%.*]], 7
; CHECK-NEXT: ret i1 [[Z]]
;
%y = sub nuw nsw i64 10, %x