[llvm] 116670d - [InstCombine] add overflow checking on Add ~X + C --> (C-1) - X

[via llvm-commits]

Author: khei4
Date: 2023-06-06T12:24:45+09:00
New Revision: 116670d192c619e2233e092e210c920d004dbe33

URL: https://github.com/llvm/llvm-project/commit/116670d192c619e2233e092e210c920d004dbe33
DIFF: https://github.com/llvm/llvm-project/commit/116670d192c619e2233e092e210c920d004dbe33.diff

LOG: [InstCombine] add overflow checking on Add ~X + C --> (C-1) - X
Differential Revision: https://reviews.llvm.org/D152088

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
    llvm/test/Transforms/InstCombine/add.ll

Removed: 
    


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diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 29409e63ab8e0..d50b2d62dea88 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -880,8 +880,15 @@ Instruction *InstCombinerImpl::foldAddWithConstant(BinaryOperator &Add) {
     return SelectInst::Create(X, InstCombiner::SubOne(Op1C), Op1);
 
   // ~X + C --> (C-1) - X
-  if (match(Op0, m_Not(m_Value(X))))
-    return BinaryOperator::CreateSub(InstCombiner::SubOne(Op1C), X);
+  if (match(Op0, m_Not(m_Value(X)))) {
+    // ~X + C has NSW and (C-1) won't oveflow => (C-1)-X can have NSW
+    auto *COne = ConstantInt::get(Op1C->getType(), 1);
+    bool WillNotSOV = willNotOverflowSignedSub(Op1C, COne, Add);
+    BinaryOperator *Res =
+        BinaryOperator::CreateSub(ConstantExpr::getSub(Op1C, COne), X);
+    Res->setHasNoSignedWrap(Add.hasNoSignedWrap() && WillNotSOV);
+    return Res;
+  }
 
   // (iN X s>> (N - 1)) + 1 --> zext (X > -1)
   const APInt *C;

diff  --git a/llvm/test/Transforms/InstCombine/add.ll b/llvm/test/Transforms/InstCombine/add.ll
index 7fac0e95b3b9f..f8b3c84ea713b 100644
--- a/llvm/test/Transforms/InstCombine/add.ll
+++ b/llvm/test/Transforms/InstCombine/add.ll
@@ -360,7 +360,7 @@ define i8 @test18(i8 %A) {
 ; ~X + -127 and (-128) - X with nsw are equally poisonous
 define i8 @test18_nsw(i8 %A) {
 ; CHECK-LABEL: @test18_nsw(
-; CHECK-NEXT:    [[C:%.*]] = sub i8 -128, [[A:%.*]]
+; CHECK-NEXT:    [[C:%.*]] = sub nsw i8 -128, [[A:%.*]]
 ; CHECK-NEXT:    ret i8 [[C]]
 ;
   %B = xor i8 %A, -1
@@ -402,7 +402,7 @@ define <2 x i64> @test18vec(<2 x i64> %A) {
 
 define <2 x i8> @test18vec_nsw(<2 x i8> %A) {
 ; CHECK-LABEL: @test18vec_nsw(
-; CHECK-NEXT:    [[C:%.*]] = sub <2 x i8> <i8 -124, i8 -125>, [[A:%.*]]
+; CHECK-NEXT:    [[C:%.*]] = sub nsw <2 x i8> <i8 -124, i8 -125>, [[A:%.*]]
 ; CHECK-NEXT:    ret <2 x i8> [[C]]
 ;
   %B = xor <2 x i8> %A, <i8 -1, i8 -1>