[DAGCombiner] Handle type-promoted constants in SDIV exact lowering (#169950)

Builds up on the solution proposed for #169491 and #169924 and applies
it for SDIV exact as well. Almost a carbon copy of UDIV exact solution
from #169949.

Author: SavchenkoValeriy

llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp

@@ -6345,7 +6345,6 @@ static SDValue BuildExactSDIV(const TargetLowering &TLI, SDNode *N,
   SDValue Op0 = N->getOperand(0);
   SDValue Op1 = N->getOperand(1);
   EVT VT = N->getValueType(0);
-  EVT SVT = VT.getScalarType();
   EVT ShVT = TLI.getShiftAmountTy(VT, DAG.getDataLayout());
   EVT ShSVT = ShVT.getScalarType();
 
@@ -6355,6 +6354,8 @@ static SDValue BuildExactSDIV(const TargetLowering &TLI, SDNode *N,
   auto BuildSDIVPattern = [&](ConstantSDNode *C) {
     if (C->isZero())
       return false;
+
+    EVT CT = C->getValueType(0);
     APInt Divisor = C->getAPIntValue();
     unsigned Shift = Divisor.countr_zero();
     if (Shift) {
@@ -6363,12 +6364,13 @@ static SDValue BuildExactSDIV(const TargetLowering &TLI, SDNode *N,
     }
     APInt Factor = Divisor.multiplicativeInverse();
     Shifts.push_back(DAG.getConstant(Shift, dl, ShSVT));
-    Factors.push_back(DAG.getConstant(Factor, dl, SVT));
+    Factors.push_back(DAG.getConstant(Factor, dl, CT));
     return true;
   };
 
   // Collect all magic values from the build vector.
-  if (!ISD::matchUnaryPredicate(Op1, BuildSDIVPattern))
+  if (!ISD::matchUnaryPredicate(Op1, BuildSDIVPattern, /*AllowUndefs=*/false,
+                                /*AllowTruncation=*/true))
     return SDValue();
 
   SDValue Shift, Factor;

llvm/test/CodeGen/AArch64/sdiv-by-const-promoted-ops.ll

@@ -75,3 +75,24 @@ define <16 x i16> @srem_v16i16_by_7(<16 x i16> %x) {
   %rem = srem <16 x i16> %x, <i16 7, i16 7, i16 7, i16 7, i16 7, i16 7, i16 7, i16 7, i16 7, i16 7, i16 7, i16 7, i16 7, i16 7, i16 7, i16 7>
   ret <16 x i16> %rem
 }
+
+define <8 x i16> @sdiv_exact_v8i16_by_255(<8 x i16> %x) {
+; CHECK-LABEL: sdiv_exact_v8i16_by_255:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    mvni v1.8h, #1, lsl #8
+; CHECK-NEXT:    mul v0.8h, v0.8h, v1.8h
+; CHECK-NEXT:    ret
+  %div = sdiv exact <8 x i16> %x, splat (i16 255)
+  ret <8 x i16> %div
+}
+
+define <16 x i16> @sdiv_exact_v16i16_by_255(<16 x i16> %x) {
+; CHECK-LABEL: sdiv_exact_v16i16_by_255:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    mvni v2.8h, #1, lsl #8
+; CHECK-NEXT:    mul v0.8h, v0.8h, v2.8h
+; CHECK-NEXT:    mul v1.8h, v1.8h, v2.8h
+; CHECK-NEXT:    ret
+  %div = sdiv exact <16 x i16> %x, splat (i16 255)
+  ret <16 x i16> %div
+}