[IndVars] Avoid unnecessary truncate for zext nneg use

When performing sext IV widening, if one of the narrow uses is in
a zext nneg, we can treat it like an sext and avoid the insertion
of a trunc.

Author: nikic

llvm/lib/Transforms/Utils/SimplifyIndVar.cpp

@@ -1762,7 +1762,7 @@ Instruction *WidenIV::widenIVUse(WidenIV::NarrowIVDefUse DU, SCEVExpander &Rewri
   };
 
   // Our raison d'etre! Eliminate sign and zero extension.
-  if ((isa<SExtInst>(DU.NarrowUse) && canWidenBySExt()) ||
+  if ((match(DU.NarrowUse, m_SExtLike(m_Value())) && canWidenBySExt()) ||
       (isa<ZExtInst>(DU.NarrowUse) && canWidenByZExt())) {
     Value *NewDef = DU.WideDef;
     if (DU.NarrowUse->getType() != WideType) {

llvm/test/Transforms/IndVarSimplify/widen-nonnegative.ll

@@ -331,9 +331,7 @@ define void @zext_nneg_add_nsw(ptr %A, i32 %offset, i32 %M) {
 ; CHECK:       for.body:
 ; CHECK-NEXT:    [[INDVARS_IV:%.*]] = phi i64 [ [[INDVARS_IV_NEXT:%.*]], [[FOR_BODY]] ], [ 0, [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    [[TMP1:%.*]] = add nsw i64 [[INDVARS_IV]], [[TMP0]]
-; CHECK-NEXT:    [[TMP2:%.*]] = trunc i64 [[TMP1]] to i32
-; CHECK-NEXT:    [[IDXPROM_US:%.*]] = zext nneg i32 [[TMP2]] to i64
-; CHECK-NEXT:    [[ARRAYIDX_US:%.*]] = getelementptr inbounds i32, ptr [[A:%.*]], i64 [[IDXPROM_US]]
+; CHECK-NEXT:    [[ARRAYIDX_US:%.*]] = getelementptr inbounds i32, ptr [[A:%.*]], i64 [[TMP1]]
 ; CHECK-NEXT:    tail call void @use_ptr(ptr [[ARRAYIDX_US]])
 ; CHECK-NEXT:    [[INDVARS_IV_NEXT]] = add nuw nsw i64 [[INDVARS_IV]], 1
 ; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp ne i64 [[INDVARS_IV_NEXT]], [[WIDE_TRIP_COUNT]]
@@ -658,9 +656,7 @@ define void @zext_nneg_mul_nsw(ptr %A, i32 %multiple, i32 %M) {
 ; CHECK:       for.body:
 ; CHECK-NEXT:    [[INDVARS_IV:%.*]] = phi i64 [ [[INDVARS_IV_NEXT:%.*]], [[FOR_BODY]] ], [ 0, [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    [[TMP1:%.*]] = mul nsw i64 [[INDVARS_IV]], [[TMP0]]
-; CHECK-NEXT:    [[TMP2:%.*]] = trunc i64 [[TMP1]] to i32
-; CHECK-NEXT:    [[IDXPROM_US:%.*]] = zext nneg i32 [[TMP2]] to i64
-; CHECK-NEXT:    [[ARRAYIDX_US:%.*]] = getelementptr inbounds i32, ptr [[A:%.*]], i64 [[IDXPROM_US]]
+; CHECK-NEXT:    [[ARRAYIDX_US:%.*]] = getelementptr inbounds i32, ptr [[A:%.*]], i64 [[TMP1]]
 ; CHECK-NEXT:    tail call void @use_ptr(ptr [[ARRAYIDX_US]])
 ; CHECK-NEXT:    [[INDVARS_IV_NEXT]] = add nuw nsw i64 [[INDVARS_IV]], 1
 ; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp ne i64 [[INDVARS_IV_NEXT]], [[WIDE_TRIP_COUNT]]