[SCEV] Also strengthen flags of expr for BEValue.

llvm/lib/Analysis/ScalarEvolution.cpp

const SCEV *ScalarEvolution::createSimpleAffineAddRec(PHINode *PN,
   }
 
   // We can add Flags to the post-inc expression only if we
   // know that it is *undefined behavior* for BEValueV to
   // overflow.
   if (auto *BEInst = dyn_cast<Instruction>(BEValueV)) {
     assert(isLoopInvariant(Accum, L) &&
            "Accum is defined outside L, but is not invariant?");
-    if (isAddRecNeverPoison(BEInst, L))
-      (void)getAddRecExpr(getAddExpr(StartVal, Accum), Accum, L, Flags);
+    if (isAddRecNeverPoison(BEInst, L)) {
+      auto *S = getAddRecExpr(getAddExpr(StartVal, Accum), Accum, L, Flags);
+      if (auto *AR = dyn_cast<SCEVAddRecExpr>(S)) {
+        setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR),
+                       (SCEV::NoWrapFlags)(AR->getNoWrapFlags() |
+                                           proveNoWrapViaConstantRanges(AR)));
+      }
+    }
   }
 
   return PHISCEV;
 }
 
 const SCEV *ScalarEvolution::createAddRecFromPHI(PHINode *PN) {
   const Loop *L = LI.getLoopFor(PN->getParent());
   if (!L || L->getHeader() != PN->getParent())
if (FoundIndex != Add->getNumOperands()) {
                          (SCEV::NoWrapFlags)(AR->getNoWrapFlags() |
                                              proveNoWrapViaConstantRanges(AR)));
         }
 
         // We can add Flags to the post-inc expression only if we
         // know that it is *undefined behavior* for BEValueV to
         // overflow.
         if (auto *BEInst = dyn_cast<Instruction>(BEValueV))
-          if (isLoopInvariant(Accum, L) && isAddRecNeverPoison(BEInst, L))
-            (void)getAddRecExpr(getAddExpr(StartVal, Accum), Accum, L, Flags);
+          if (isLoopInvariant(Accum, L) && isAddRecNeverPoison(BEInst, L)) {
+            auto *S =
+                getAddRecExpr(getAddExpr(StartVal, Accum), Accum, L, Flags);
+            if (auto *AR = dyn_cast<SCEVAddRecExpr>(S)) {
+              setNoWrapFlags(
+                  const_cast<SCEVAddRecExpr *>(AR),
+                  (SCEV::NoWrapFlags)(AR->getNoWrapFlags() |
+                                      proveNoWrapViaConstantRanges(AR)));
+            }
+          }
 
         return PHISCEV;
       }
     }
   } else {
     // Otherwise, this could be a loop like this:
     //     i = 0;  for (j = 1; ..; ++j) { ....  i = j; }
     // In this case, j = {1,+,1}  and BEValue is j.

llvm/test/Analysis/ScalarEvolution/trip-count-negative-stride.ll

 
 for.end:                                          ; preds = %for.body, %entry
   ret void
 }
 
 define void @ult_129_unknown_start(i8 %start) mustprogress {
 ; CHECK-LABEL: 'ult_129_unknown_start'
 ; CHECK-NEXT:  Determining loop execution counts for: @ult_129_unknown_start
-; CHECK-NEXT:  Loop %for.body: backedge-taken count is 0
-; CHECK-NEXT:  Loop %for.body: constant max backedge-taken count is 0
-; CHECK-NEXT:  Loop %for.body: symbolic max backedge-taken count is 0
-; CHECK-NEXT:  Loop %for.body: Predicated backedge-taken count is 0
+; CHECK-NEXT:  Loop %for.body: backedge-taken count is (((127 + (-1 * (1 umin (127 + (-1 * %start) + (-128 umax (-127 + %start)<nuw>))))<nuw><nsw> + (-1 * %start) + (-128 umax (-127 + %start)<nuw>)) /u -127) + (1 umin (127 + (-1 * %start) + (-128 umax (-127 + %start)<nuw>))))
+; CHECK-NEXT:  Loop %for.body: constant max backedge-taken count is 1
+; CHECK-NEXT:  Loop %for.body: symbolic max backedge-taken count is (((127 + (-1 * (1 umin (127 + (-1 * %start) + (-128 umax (-127 + %start)<nuw>))))<nuw><nsw> + (-1 * %start) + (-128 umax (-127 + %start)<nuw>)) /u -127) + (1 umin (127 + (-1 * %start) + (-128 umax (-127 + %start)<nuw>))))
+; CHECK-NEXT:  Loop %for.body: Predicated backedge-taken count is (((127 + (-1 * (1 umin (127 + (-1 * %start) + (-128 umax (-127 + %start)<nuw>))))<nuw><nsw> + (-1 * %start) + (-128 umax (-127 + %start)<nuw>)) /u -127) + (1 umin (127 + (-1 * %start) + (-128 umax (-127 + %start)<nuw>))))
 ; CHECK-NEXT:   Predicates:
 ; CHECK:       Loop %for.body: Trip multiple is 1
 ;
 entry:
   br label %for.body
 
 for.body:                                         ; preds = %entry, %for.body
   %i.05 = phi i8 [ %add, %for.body ], [ %start, %entry ]