[LegalizeTypes][X86] Use getShiftAmountConstant in ExpandIntRes_SIGN_EXTEND. (#158388)

This ensures we don't need to fixup the shift amount later.

Unfortunately, this enabled the
(SRA (SHL X, ShlConst), SraConst) -> (SRA (sext_in_reg X), SraConst -
ShlConst) combine in combineShiftRightArithmetic for some cases in
is_fpclass-fp80.ll. So we need to also update checkSignTestSetCCCombine
to look through sign_extend_inreg to prevent a regression.

Author: topperc

llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp

@@ -5088,9 +5088,8 @@ void DAGTypeLegalizer::ExpandIntRes_SIGN_EXTEND(SDNode *N,
     Lo = DAG.getNode(ISD::SIGN_EXTEND, dl, NVT, N->getOperand(0));
     // The high part is obtained by SRA'ing all but one of the bits of low part.
     unsigned LoSize = NVT.getSizeInBits();
-    Hi = DAG.getNode(
-        ISD::SRA, dl, NVT, Lo,
-        DAG.getConstant(LoSize - 1, dl, TLI.getPointerTy(DAG.getDataLayout())));
+    Hi = DAG.getNode(ISD::SRA, dl, NVT, Lo,
+                     DAG.getShiftAmountConstant(LoSize - 1, NVT, dl));
   } else {
     // For example, extension of an i48 to an i64.  The operand type necessarily
     // promotes to the result type, so will end up being expanded too.
@@ -5123,8 +5122,8 @@ ExpandIntRes_SIGN_EXTEND_INREG(SDNode *N, SDValue &Lo, SDValue &Hi) {
     // The high part gets the sign extension from the lo-part.  This handles
     // things like sextinreg V:i64 from i8.
     Hi = DAG.getNode(ISD::SRA, dl, Hi.getValueType(), Lo,
-                     DAG.getConstant(Hi.getValueSizeInBits() - 1, dl,
-                                     TLI.getPointerTy(DAG.getDataLayout())));
+                     DAG.getShiftAmountConstant(Hi.getValueSizeInBits() - 1,
+                                                Hi.getValueType(), dl));
   } else {
     // For example, extension of an i48 to an i64.  Leave the low part alone,
     // sext_inreg the high part.

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -48396,13 +48396,17 @@ static SDValue checkSignTestSetCCCombine(SDValue Cmp, X86::CondCode &CC,
   MVT SrcVT = Src.getSimpleValueType();
   APInt BitMask = APInt::getSignMask(SrcVT.getScalarSizeInBits());
 
-  // If Src came from a SHL (probably from an expanded SIGN_EXTEND_INREG), then
-  // peek through and adjust the TEST bit.
+  // If Src came from a SIGN_EXTEND_INREG or SHL (probably from an expanded
+  // SIGN_EXTEND_INREG), then peek through and adjust the TEST bit.
   if (Src.getOpcode() == ISD::SHL) {
     if (std::optional<unsigned> ShiftAmt = DAG.getValidShiftAmount(Src)) {
       Src = Src.getOperand(0);
       BitMask.lshrInPlace(*ShiftAmt);
     }
+  } else if (Src.getOpcode() == ISD::SIGN_EXTEND_INREG) {
+    EVT ExtVT = cast<VTSDNode>(Src.getOperand(1))->getVT();
+    Src = Src.getOperand(0);
+    BitMask.lshrInPlace(BitMask.getBitWidth() - ExtVT.getScalarSizeInBits());
   }
 
   SDValue Mask = DAG.getNode(ISD::AND, DL, SrcVT, Src,