[PATCH] D60396: [InstCombine] sdiv exact flag fixup

[ChenZheng via Phabricator via llvm-commits]

shchenz created this revision.
shchenz added reviewers: spatel, lebedev.ri, RKSimon.
Herald added a subscriber: hiraditya.
Herald added a project: LLVM.

This is a issue found when investigate https://reviews.llvm.org/D60395.
**exact** flag is missing when opt combine ` 0 - (X sdiv C) ` -> ` (X sdiv -C)`


https://reviews.llvm.org/D60396

Files:
  llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
  llvm/test/Transforms/InstCombine/div.ll


Index: llvm/test/Transforms/InstCombine/div.ll
===================================================================
--- llvm/test/Transforms/InstCombine/div.ll
+++ llvm/test/Transforms/InstCombine/div.ll
@@ -762,7 +762,7 @@
 
 define i32 @test_exact(i32 %x) {
 ; CHECK-LABEL: @test_exact(
-; CHECK-NEXT:    [[DIV:%.*]] = sdiv i32 [[X:%.*]], -3
+; CHECK-NEXT:    [[DIV:%.*]] = sdiv exact i32 [[X:%.*]], -3
 ; CHECK-NEXT:    ret i32 [[DIV]]
 ;
   %div = sdiv exact i32 %x, 3
@@ -772,7 +772,7 @@
 
 define <2 x i64> @test_exact_vec(<2 x i64> %x) {
 ; CHECK-LABEL: @test_exact_vec(
-; CHECK-NEXT:    [[DIV:%.*]] = sdiv <2 x i64> [[X:%.*]], <i64 -3, i64 -4>
+; CHECK-NEXT:    [[DIV:%.*]] = sdiv exact <2 x i64> [[X:%.*]], <i64 -3, i64 -4>
 ; CHECK-NEXT:    ret <2 x i64> [[DIV]]
 ;
   %div = sdiv exact <2 x i64> %x, <i64 3, i64 4>
Index: llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1693,8 +1693,11 @@
 
     // 0 - (X sdiv C)  -> (X sdiv -C)  provided the negation doesn't overflow.
     if (match(Op1, m_SDiv(m_Value(X), m_Constant(C))) && match(Op0, m_Zero()) &&
-        C->isNotMinSignedValue() && !C->isOneValue())
-      return BinaryOperator::CreateSDiv(X, ConstantExpr::getNeg(C));
+        C->isNotMinSignedValue() && !C->isOneValue()) {
+      auto *BO = BinaryOperator::CreateSDiv(X, ConstantExpr::getNeg(C));
+      BO->setIsExact(cast<BinaryOperator>(Op1)->isExact());
+      return BO;
+    }
 
     // 0 - (X << Y)  -> (-X << Y)   when X is freely negatable.
     if (match(Op1, m_Shl(m_Value(X), m_Value(Y))) && match(Op0, m_Zero()))


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