[SCEV] Use ashr to adjust constant multipliers

Author: dtcxzyw

llvm/lib/Analysis/ScalarEvolution.cpp

@@ -7841,7 +7841,7 @@ const SCEV *ScalarEvolution::createSCEV(Value *V) {
               unsigned GCD = std::min(MulZeros, TZ);
               APInt DivAmt = APInt::getOneBitSet(BitWidth, TZ - GCD);
               SmallVector<const SCEV*, 4> MulOps;
-              MulOps.push_back(getConstant(OpC->getAPInt().lshr(GCD)));
+              MulOps.push_back(getConstant(OpC->getAPInt().ashr(GCD)));
               append_range(MulOps, LHSMul->operands().drop_front());
               auto *NewMul = getMulExpr(MulOps, LHSMul->getNoWrapFlags());
               ShiftedLHS = getUDivExpr(NewMul, getConstant(DivAmt));

llvm/test/Analysis/ScalarEvolution/pr135531.ll

@@ -9,7 +9,7 @@ define i32 @pr135511(i32 %x) {
 ; CHECK-NEXT:    %neg = sub nsw i32 0, %and
 ; CHECK-NEXT:    --> (-2 * (zext i13 (trunc i32 (%x /u 2) to i13) to i32))<nsw> U: [0,-1) S: [-16382,1)
 ; CHECK-NEXT:    %res = and i32 %neg, 268431360
-; CHECK-NEXT:    --> (4096 * (zext i16 (trunc i32 ((2147483647 * (zext i13 (trunc i32 (%x /u 2) to i13) to i32))<nuw><nsw> /u 2048) to i16) to i32))<nuw><nsw> U: [0,268431361) S: [0,268431361)
+; CHECK-NEXT:    --> (4096 * (zext i16 (trunc i32 ((-1 * (zext i13 (trunc i32 (%x /u 2) to i13) to i32))<nsw> /u 2048) to i16) to i32))<nuw><nsw> U: [0,268431361) S: [0,268431361)
 ; CHECK-NEXT:  Determining loop execution counts for: @pr135511
 ;
   %and = and i32 %x, 16382