[llvm] 5060f56 - [InstCombine] (-NSW x) s> x --> x s< 0 (PR39480)
Roman Lebedev via llvm-commits
llvm-commits at lists.llvm.org
Thu Aug 6 01:51:41 PDT 2020
Author: Roman Lebedev
Date: 2020-08-06T11:50:34+03:00
New Revision: 5060f5682b011d2a8c708b3c1b16bd4e0c408afb
URL: https://github.com/llvm/llvm-project/commit/5060f5682b011d2a8c708b3c1b16bd4e0c408afb
DIFF: https://github.com/llvm/llvm-project/commit/5060f5682b011d2a8c708b3c1b16bd4e0c408afb.diff
LOG: [InstCombine] (-NSW x) s> x --> x s< 0 (PR39480)
Name: (-x) s> x --> x s< 0
%neg_x = sub nsw i8 0, %x ; %x must not be INT_MIN
%r = icmp sgt i8 %neg_x, %x
=>
%r = icmp slt i8 %x, 0
https://rise4fun.com/Alive/ZslD
https://bugs.llvm.org/show_bug.cgi?id=39480
Added:
Modified:
llvm/include/llvm/IR/PatternMatch.h
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
llvm/test/Transforms/InstCombine/cmp-x-vs-neg-x.ll
Removed:
################################################################################
diff --git a/llvm/include/llvm/IR/PatternMatch.h b/llvm/include/llvm/IR/PatternMatch.h
index 4c11bc82510b..0850835aa014 100644
--- a/llvm/include/llvm/IR/PatternMatch.h
+++ b/llvm/include/llvm/IR/PatternMatch.h
@@ -2048,6 +2048,15 @@ m_Neg(const ValTy &V) {
return m_Sub(m_ZeroInt(), V);
}
+/// Matches a 'Neg' as 'sub nsw 0, V'.
+template <typename ValTy>
+inline OverflowingBinaryOp_match<cst_pred_ty<is_zero_int>, ValTy,
+ Instruction::Sub,
+ OverflowingBinaryOperator::NoSignedWrap>
+m_NSWNeg(const ValTy &V) {
+ return m_NSWSub(m_ZeroInt(), V);
+}
+
/// Matches a 'Not' as 'xor V, -1' or 'xor -1, V'.
template <typename ValTy>
inline BinaryOp_match<ValTy, cst_pred_ty<is_all_ones>, Instruction::Xor, true>
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 7aa3126e1754..0032b65c3d2a 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -3719,6 +3719,27 @@ Value *InstCombinerImpl::foldUnsignedMultiplicationOverflowCheck(ICmpInst &I) {
return Res;
}
+Instruction *foldICmpXNegX(ICmpInst &I) {
+ CmpInst::Predicate Pred;
+ Value *X;
+ if (!match(&I, m_c_ICmp(Pred, m_NSWNeg(m_Value(X)), m_Deferred(X))))
+ return nullptr;
+
+ CmpInst::Predicate NewPred;
+ Constant *NewRHS;
+ switch (Pred) {
+ case ICmpInst::ICMP_SGT:
+ NewPred = ICmpInst::ICMP_SLT;
+ NewRHS = Constant::getNullValue(X->getType());
+ break;
+
+ default:
+ return nullptr;
+ }
+
+ return ICmpInst::Create(Instruction::ICmp, NewPred, X, NewRHS, I.getName());
+}
+
/// Try to fold icmp (binop), X or icmp X, (binop).
/// TODO: A large part of this logic is duplicated in InstSimplify's
/// simplifyICmpWithBinOp(). We should be able to share that and avoid the code
@@ -3734,6 +3755,9 @@ Instruction *InstCombinerImpl::foldICmpBinOp(ICmpInst &I,
if (!BO0 && !BO1)
return nullptr;
+ if (Instruction *NewICmp = foldICmpXNegX(I))
+ return NewICmp;
+
const CmpInst::Predicate Pred = I.getPredicate();
Value *X;
diff --git a/llvm/test/Transforms/InstCombine/cmp-x-vs-neg-x.ll b/llvm/test/Transforms/InstCombine/cmp-x-vs-neg-x.ll
index a839ac6e979a..485e32913601 100644
--- a/llvm/test/Transforms/InstCombine/cmp-x-vs-neg-x.ll
+++ b/llvm/test/Transforms/InstCombine/cmp-x-vs-neg-x.ll
@@ -6,8 +6,7 @@ declare void @use8(i8)
define i1 @t0(i8 %x) {
; CHECK-LABEL: @t0(
-; CHECK-NEXT: [[NEG_X:%.*]] = sub nsw i8 0, [[X:%.*]]
-; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i8 [[NEG_X]], [[X]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp slt i8 [[X:%.*]], 0
; CHECK-NEXT: ret i1 [[CMP]]
;
%neg_x = sub nsw i8 0, %x
@@ -18,8 +17,7 @@ define i1 @t0(i8 %x) {
define i1 @t0_commutative() {
; CHECK-LABEL: @t0_commutative(
; CHECK-NEXT: [[X:%.*]] = call i8 @gen8()
-; CHECK-NEXT: [[NEG_X:%.*]] = sub nsw i8 0, [[X]]
-; CHECK-NEXT: [[CMP:%.*]] = icmp slt i8 [[X]], [[NEG_X]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp slt i8 [[X]], 0
; CHECK-NEXT: ret i1 [[CMP]]
;
%x = call i8 @gen8()
@@ -32,7 +30,7 @@ define i1 @t0_extrause(i8 %x) {
; CHECK-LABEL: @t0_extrause(
; CHECK-NEXT: [[NEG_X:%.*]] = sub nsw i8 0, [[X:%.*]]
; CHECK-NEXT: call void @use8(i8 [[NEG_X]])
-; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i8 [[NEG_X]], [[X]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp slt i8 [[X]], 0
; CHECK-NEXT: ret i1 [[CMP]]
;
%neg_x = sub nsw i8 0, %x
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