[RISCV] Truncate constants to eltwidth before checking simm5 when con… (llvm#67062)

…verting VMV_V_X to VMV_X_S.

Instruction selection knows the bits past EltWidth are ignored, we
should do the same here.

Author: topperc

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -14435,7 +14435,8 @@ SDValue RISCVTargetLowering::PerformDAGCombine(SDNode *N,
     // patterns on rv32..
     ConstantSDNode *Const = dyn_cast<ConstantSDNode>(Scalar);
     if (isOneConstant(VL) && EltWidth <= Subtarget.getXLen() &&
-        (!Const || Const->isZero() || !isInt<5>(Const->getSExtValue())))
+        (!Const || Const->isZero() ||
+         !Const->getAPIntValue().sextOrTrunc(EltWidth).isSignedIntN(5)))
       return DAG.getNode(RISCVISD::VMV_S_X_VL, DL, VT, Passthru, Scalar, VL);
 
     break;

llvm/test/CodeGen/RISCV/rvv/fixed-vectors-int-shuffles.ll

@@ -781,3 +781,16 @@ define <8 x i8> @unmergable(<8 x i8> %v, <8 x i8> %w) {
   %res = shufflevector <8 x i8> %v, <8 x i8> %w, <8 x i32> <i32 2, i32 9, i32 4, i32 11, i32 6, i32 13, i32 8, i32 15>
   ret <8 x i8> %res
 }
+
+; Make sure we use a vmv.v.i to load the mask constant.
+define <8 x i32> @shuffle_v8i32_2(<8 x i32> %x, <8 x i32> %y) {
+; CHECK-LABEL: shuffle_v8i32_2:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vsetivli zero, 1, e8, mf8, ta, ma
+; CHECK-NEXT:    vmv.v.i v0, -13
+; CHECK-NEXT:    vsetivli zero, 8, e32, m2, ta, ma
+; CHECK-NEXT:    vmerge.vvm v8, v10, v8, v0
+; CHECK-NEXT:    ret
+  %s = shufflevector <8 x i32> %x, <8 x i32> %y, <8 x i32> <i32 0, i32 1, i32 10, i32 11, i32 4, i32 5, i32 6, i32 7>
+  ret <8 x i32> %s
+}