Automerge: [LICM] Use OverflowTracking to preserve NUW/NSW when reassociating. (#140404)

This enables preserving NSW when both adds have NSW and NUW.

For now, set AllKnownNonNegative/AllKnownNonZero to false when using in
LICM.

https://alive2.llvm.org/ce/z/uu79Xc

Depends on llvm/llvm-project#140403.

PR: llvm/llvm-project#140404

Author: fhahn

llvm/lib/Transforms/Scalar/LICM.cpp

@@ -2864,14 +2864,7 @@ static bool hoistBOAssociation(Instruction &I, Loop &L,
   auto *NewBO = BinaryOperator::Create(
       Opcode, LV, Inv, BO->getName() + ".reass", BO->getIterator());
 
-  // Copy NUW for ADDs if both instructions have it.
-  if (Opcode == Instruction::Add && BO->hasNoUnsignedWrap() &&
-      BO0->hasNoUnsignedWrap()) {
-    // If `Inv` was not constant-folded, a new Instruction has been created.
-    if (auto *I = dyn_cast<Instruction>(Inv))
-      I->setHasNoUnsignedWrap(true);
-    NewBO->setHasNoUnsignedWrap(true);
-  } else if (Opcode == Instruction::FAdd || Opcode == Instruction::FMul) {
+  if (Opcode == Instruction::FAdd || Opcode == Instruction::FMul) {
     // Intersect FMF flags for FADD and FMUL.
     FastMathFlags Intersect = BO->getFastMathFlags() & BO0->getFastMathFlags();
     if (auto *I = dyn_cast<Instruction>(Inv))
@@ -2884,6 +2877,16 @@ static bool hoistBOAssociation(Instruction &I, Loop &L,
     if (auto *I = dyn_cast<PossiblyDisjointInst>(Inv))
       I->setIsDisjoint(Disjoint);
     cast<PossiblyDisjointInst>(NewBO)->setIsDisjoint(Disjoint);
+  } else {
+    OverflowTracking Flags;
+    Flags.AllKnownNonNegative = false;
+    Flags.AllKnownNonZero = false;
+    Flags.mergeFlags(*BO);
+    Flags.mergeFlags(*BO0);
+    // If `Inv` was not constant-folded, a new Instruction has been created.
+    if (auto *I = dyn_cast<Instruction>(Inv))
+      Flags.applyFlags(*I);
+    Flags.applyFlags(*NewBO);
   }
 
   BO->replaceAllUsesWith(NewBO);

llvm/test/Transforms/LICM/hoist-binop.ll

@@ -371,13 +371,13 @@ loop:
 define void @add_nuw_nsw(i64 %c1, i64 %c2) {
 ; CHECK-LABEL: @add_nuw_nsw(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[INVARIANT_OP:%.*]] = add nuw i64 [[C1:%.*]], [[C2:%.*]]
+; CHECK-NEXT:    [[INVARIANT_OP:%.*]] = add nuw nsw i64 [[C1:%.*]], [[C2:%.*]]
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
 ; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[INDEX_NEXT_REASS:%.*]], [[LOOP]] ]
 ; CHECK-NEXT:    [[STEP_ADD:%.*]] = add nuw nsw i64 [[INDEX]], [[C1]]
 ; CHECK-NEXT:    call void @use(i64 [[STEP_ADD]])
-; CHECK-NEXT:    [[INDEX_NEXT_REASS]] = add nuw i64 [[INDEX]], [[INVARIANT_OP]]
+; CHECK-NEXT:    [[INDEX_NEXT_REASS]] = add nuw nsw i64 [[INDEX]], [[INVARIANT_OP]]
 ; CHECK-NEXT:    br label [[LOOP]]
 ;
 entry: