[IndVars] Generate zext nneg when locally obvious

llvm/lib/Transforms/Utils/SimplifyIndVar.cpp

@@ -1200,6 +1200,16 @@ Value *WidenIV::createExtendInst(Value *NarrowOper, Type *WideType,
        L = L->getParentLoop())
     Builder.SetInsertPoint(L->getLoopPreheader()->getTerminator());
 
+  // If we know the operand is never negative, prefer zext nneg.
+  // For constant expressions, fall back to plain sext or zext.
+  if (SE->isKnownNonNegative(SE->getSCEV(NarrowOper))) {
+    auto *Res = Builder.CreateZExt(NarrowOper, WideType);
+    if (auto I = dyn_cast<Instruction>(Res)) {
+      I->setNonNeg(true);
+      return I;
+    }
+  }
+
   return IsSigned ? Builder.CreateSExt(NarrowOper, WideType) :
                     Builder.CreateZExt(NarrowOper, WideType);
 }
@@ -1685,6 +1695,17 @@ bool WidenIV::widenWithVariantUse(WidenIV::NarrowIVDefUse DU) {
     auto ExtendedOp = [&](Value * V)->Value * {
       if (V == NarrowUse)
         return WideBO;
+
+      // If we know the operand is never negative, prefer zext nneg.
+      // For constant expressions, fall back to plain sext or zext.
+      if (SE->isKnownNonNegative(SE->getSCEV(V))) {
+        auto *Res = Builder.CreateZExt(V, WideBO->getType());
+        if (auto I = dyn_cast<Instruction>(Res)) {
+          I->setNonNeg(true);
+          return I;
+        }
+      }
+
       if (ExtKind == ExtendKind::Zero)
         return Builder.CreateZExt(V, WideBO->getType());
       else

llvm/test/Analysis/ScalarEvolution/guards.ll

@@ -57,7 +57,7 @@ define void @test_2(i32 %n, ptr %len_buf) {
 ; CHECK-SAME: (i32 [[N:%.*]], ptr [[LEN_BUF:%.*]]) {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[LEN:%.*]] = load i32, ptr [[LEN_BUF]], align 4, !range [[RNG1:![0-9]+]]
-; CHECK-NEXT:    [[TMP0:%.*]] = zext i32 [[LEN]] to i64
+; CHECK-NEXT:    [[TMP0:%.*]] = zext nneg i32 [[LEN]] to i64
 ; CHECK-NEXT:    [[TMP1:%.*]] = zext i32 [[N]] to i64
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:

llvm/test/Transforms/IndVarSimplify/X86/pr59615.ll

@@ -17,7 +17,7 @@ define void @test() {
 ; CHECK-NEXT:    ret void
 ; CHECK:       bb8:
 ; CHECK-NEXT:    [[VAR9:%.*]] = load atomic i32, ptr addrspace(1) poison unordered, align 8, !range [[RNG0]], !invariant.load !1, !noundef !1
-; CHECK-NEXT:    [[TMP0:%.*]] = zext i32 [[VAR9]] to i64
+; CHECK-NEXT:    [[TMP0:%.*]] = zext nneg i32 [[VAR9]] to i64
 ; CHECK-NEXT:    [[VAR10:%.*]] = icmp ult i64 [[INDVARS_IV]], [[TMP0]]
 ; CHECK-NEXT:    br i1 [[VAR10]], label [[BB12]], label [[BB11:%.*]]
 ; CHECK:       bb11:

llvm/test/Transforms/IndVarSimplify/post-inc-range.ll

@@ -120,7 +120,7 @@ define void @test_range_metadata(ptr %array_length_ptr, ptr %base,
 ; CHECK:       for.body:
 ; CHECK-NEXT:    [[INDVARS_IV:%.*]] = phi i64 [ [[INDVARS_IV_NEXT:%.*]], [[FOR_INC:%.*]] ], [ [[TMP0]], [[FOR_BODY_LR_PH:%.*]] ]
 ; CHECK-NEXT:    [[ARRAY_LENGTH:%.*]] = load i32, ptr [[ARRAY_LENGTH_PTR:%.*]], align 4, !range [[RNG0:![0-9]+]]
-; CHECK-NEXT:    [[TMP2:%.*]] = zext i32 [[ARRAY_LENGTH]] to i64
+; CHECK-NEXT:    [[TMP2:%.*]] = zext nneg i32 [[ARRAY_LENGTH]] to i64
 ; CHECK-NEXT:    [[WITHIN_LIMITS:%.*]] = icmp ult i64 [[INDVARS_IV]], [[TMP2]]
 ; CHECK-NEXT:    br i1 [[WITHIN_LIMITS]], label [[CONTINUE:%.*]], label [[FOR_END:%.*]]
 ; CHECK:       continue:

llvm/test/Transforms/LoopFlatten/widen-iv.ll

@@ -156,7 +156,7 @@ define void @foo2_sext(i32* nocapture readonly %A, i32 %N, i32 %M) {
 ; CHECK-NEXT:    [[INDVAR:%.*]] = phi i64 [ 0, [[FOR_COND1_PREHEADER_US]] ]
 ; CHECK-NEXT:    [[J_016_US:%.*]] = phi i32 [ 0, [[FOR_COND1_PREHEADER_US]] ]
 ; CHECK-NEXT:    [[TMP5:%.*]] = add nsw i64 [[INDVAR]], [[TMP3]]
-; CHECK-NEXT:    [[TMP6:%.*]] = sext i32 [[J_016_US]] to i64
+; CHECK-NEXT:    [[TMP6:%.*]] = zext nneg i32 [[J_016_US]] to i64
 ; CHECK-NEXT:    [[TMP7:%.*]] = add nsw i64 [[TMP6]], [[TMP3]]
 ; CHECK-NEXT:    [[ADD_US:%.*]] = add nsw i32 [[J_016_US]], [[MUL_US]]
 ; CHECK-NEXT:    [[IDXPROM_US:%.*]] = sext i32 [[FLATTEN_TRUNCIV]] to i64

llvm/test/Transforms/LoopFlatten/widen-iv2.ll

@@ -39,7 +39,7 @@ define dso_local i32 @fn1() local_unnamed_addr #0 {
 ; CHECK-NEXT:    [[INDVAR:%.*]] = phi i64 [ [[INDVAR_NEXT:%.*]], [[FOR_BODY3_US]] ], [ 0, [[FOR_COND1_PREHEADER_US]] ]
 ; CHECK-NEXT:    [[J_014_US:%.*]] = phi i32 [ 0, [[FOR_COND1_PREHEADER_US]] ], [ [[INC_US:%.*]], [[FOR_BODY3_US]] ]
 ; CHECK-NEXT:    [[TMP7:%.*]] = add nsw i64 [[INDVAR]], [[TMP5]]
-; CHECK-NEXT:    [[TMP8:%.*]] = sext i32 [[J_014_US]] to i64
+; CHECK-NEXT:    [[TMP8:%.*]] = zext nneg i32 [[J_014_US]] to i64
 ; CHECK-NEXT:    [[TMP9:%.*]] = add nsw i64 [[TMP8]], [[TMP5]]
 ; CHECK-NEXT:    [[ADD_US:%.*]] = add nsw i32 [[J_014_US]], [[MUL_US]]
 ; CHECK-NEXT:    [[IDXPROM_US:%.*]] = sext i32 [[ADD_US]] to i64

llvm/test/Transforms/LoopFlatten/widen-iv3.ll

@@ -18,7 +18,7 @@ define i16 @foo() {
 ; CHECK-NEXT:    [[SUM_012:%.*]] = phi i16 [ 0, [[ENTRY]] ], [ [[ADD5_LCSSA:%.*]], [[FOR_COND_CLEANUP3]] ]
 ; CHECK-NEXT:    [[TMP0:%.*]] = mul nsw i32 [[INDVAR2]], 16
 ; CHECK-NEXT:    [[MUL:%.*]] = mul nsw i16 [[I_013]], 16
-; CHECK-NEXT:    [[TMP1:%.*]] = zext i16 [[MUL]] to i32
+; CHECK-NEXT:    [[TMP1:%.*]] = zext nneg i16 [[MUL]] to i32
 ; CHECK-NEXT:    br label [[FOR_BODY4:%.*]]
 ; CHECK:       for.cond.cleanup:
 ; CHECK-NEXT:    [[ADD5_LCSSA_LCSSA:%.*]] = phi i16 [ [[ADD5_LCSSA]], [[FOR_COND_CLEANUP3]] ]