[SDAG][X86] Remove hack needed to avoid missing x87 FPU stack pops

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -2635,22 +2635,6 @@ bool SelectionDAG::expandMultipleResultFPLibCall(
     Results.push_back(LoadResult);
   }
 
-  if (CallRetResNo && !Node->hasAnyUseOfValue(*CallRetResNo)) {
-    // FIXME: Find a way to avoid updating the root. This is needed for x86,
-    // which uses a floating-point stack. If (for example) the node to be
-    // expanded has two results one floating-point which is returned by the
-    // call, and one integer result, returned via an output pointer. If only the
-    // integer result is used then the `CopyFromReg` for the FP result may be
-    // optimized out. This prevents an FP stack pop from being emitted for it.
-    // Setting the root like this ensures there will be a use of the
-    // `CopyFromReg` chain, and ensures the FP pop will be emitted.
-    SDValue NewRoot =
-        getNode(ISD::TokenFactor, DL, MVT::Other, getRoot(), CallChain);
-    setRoot(NewRoot);
-    // Ensure the new root is reachable from the results.
-    Results[0] = getMergeValues({Results[0], NewRoot}, DL);
-  }
-
   return true;
 }
 

llvm/lib/Target/X86/X86ISelDAGToDAG.cpp

@@ -6717,6 +6717,17 @@ void X86DAGToDAGISel::Select(SDNode *Node) {
     ReplaceNode(Node, Res);
     return;
   }
+  case X86ISD::POP_FROM_X87_REG: {
+    SDValue Chain = Node->getOperand(0);
+    Register Reg = cast<RegisterSDNode>(Node->getOperand(1))->getReg();
+    SDValue Glue;
+    if (Node->getNumValues() == 3)
+      Glue = Node->getOperand(2);
+    SDValue Copy =
+        CurDAG->getCopyFromReg(Chain, dl, Reg, Node->getValueType(0), Glue);
+    ReplaceNode(Node, Copy.getNode());
+    return;
+  }
   }
 
   SelectCode(Node);

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -35114,6 +35114,7 @@ const char *X86TargetLowering::getTargetNodeName(unsigned Opcode) const {
   NODE_NAME_CASE(CVTTP2SIS_SAE)
   NODE_NAME_CASE(CVTTP2UIS)
   NODE_NAME_CASE(MCVTTP2UIS)
+  NODE_NAME_CASE(POP_FROM_X87_REG)
   }
   return nullptr;
 #undef NODE_NAME_CASE

llvm/lib/Target/X86/X86ISelLowering.h

@@ -81,6 +81,15 @@ namespace llvm {
     // marker instruction.
     CALL_RVMARKER,
 
+    /// The same as ISD::CopyFromReg except that this node makes it explicit
+    /// that it may lower to an x87 FPU stack pop. Optimizations should be more
+    /// cautious when handling this node than a normal CopyFromReg to avoid
+    /// removing a required FPU stack pop. A key requirement is optimizations
+    /// should not optimize any users of a chain that contains a
+    /// POP_FROM_X87_REG to use a chain from a point earlier than the
+    /// POP_FROM_X87_REG (which may remove a required FPU stack pop).
+    POP_FROM_X87_REG,
+
     /// X86 compare and logical compare instructions.
     CMP,
     FCMP,

llvm/lib/Target/X86/X86ISelLoweringCall.cpp

@@ -1095,6 +1095,15 @@ static SDValue lowerRegToMasks(const SDValue &ValArg, const EVT &ValVT,
   return DAG.getBitcast(ValVT, ValReturned);
 }
 
+static SDValue getPopFromX87Reg(SelectionDAG &DAG, SDValue Chain,
+                                const SDLoc &dl, Register Reg, EVT VT,
+                                SDValue Glue) {
+  SDVTList VTs = DAG.getVTList(VT, MVT::Other, MVT::Glue);
+  SDValue Ops[] = {Chain, DAG.getRegister(Reg, VT), Glue};
+  return DAG.getNode(X86ISD::POP_FROM_X87_REG, dl, VTs,
+                     ArrayRef(Ops, Glue.getNode() ? 3 : 2));
+}
+
 /// Lower the result values of a call into the
 /// appropriate copies out of appropriate physical registers.
 ///
@@ -1145,8 +1154,8 @@ SDValue X86TargetLowering::LowerCallResult(
     // If we prefer to use the value in xmm registers, copy it out as f80 and
     // use a truncate to move it from fp stack reg to xmm reg.
     bool RoundAfterCopy = false;
-    if ((VA.getLocReg() == X86::FP0 || VA.getLocReg() == X86::FP1) &&
-        isScalarFPTypeInSSEReg(VA.getValVT())) {
+    bool X87Result = VA.getLocReg() == X86::FP0 || VA.getLocReg() == X86::FP1;
+    if (X87Result && isScalarFPTypeInSSEReg(VA.getValVT())) {
       if (!Subtarget.hasX87())
         report_fatal_error("X87 register return with X87 disabled");
       CopyVT = MVT::f80;
@@ -1160,8 +1169,12 @@ SDValue X86TargetLowering::LowerCallResult(
       Val =
           getv64i1Argument(VA, RVLocs[++I], Chain, DAG, dl, Subtarget, &InGlue);
     } else {
-      Chain = DAG.getCopyFromReg(Chain, dl, VA.getLocReg(), CopyVT, InGlue)
-                  .getValue(1);
+      Chain =
+          X87Result
+              ? getPopFromX87Reg(DAG, Chain, dl, VA.getLocReg(), CopyVT, InGlue)
+                    .getValue(1)
+              : DAG.getCopyFromReg(Chain, dl, VA.getLocReg(), CopyVT, InGlue)
+                    .getValue(1);
       Val = Chain.getValue(0);
       InGlue = Chain.getValue(2);
     }

llvm/test/CodeGen/PowerPC/llvm.modf.ll

@@ -328,3 +328,108 @@ define { ppc_fp128, ppc_fp128 } @test_modf_ppcf128(ppc_fp128 %a) {
   %result = call { ppc_fp128, ppc_fp128 } @llvm.modf.ppcf128(ppc_fp128 %a)
   ret { ppc_fp128, ppc_fp128 } %result
 }
+
+define ppc_fp128 @test_modf_ppcf128_only_use_intergral(ppc_fp128 %a) {
+; CHECK-LABEL: test_modf_ppcf128_only_use_intergral:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    mflr r0
+; CHECK-NEXT:    stdu r1, -48(r1)
+; CHECK-NEXT:    std r0, 64(r1)
+; CHECK-NEXT:    .cfi_def_cfa_offset 48
+; CHECK-NEXT:    .cfi_offset lr, 16
+; CHECK-NEXT:    addi r5, r1, 32
+; CHECK-NEXT:    bl modfl
+; CHECK-NEXT:    nop
+; CHECK-NEXT:    lfd f1, 32(r1)
+; CHECK-NEXT:    lfd f2, 40(r1)
+; CHECK-NEXT:    addi r1, r1, 48
+; CHECK-NEXT:    ld r0, 16(r1)
+; CHECK-NEXT:    mtlr r0
+; CHECK-NEXT:    blr
+  %result = call { ppc_fp128, ppc_fp128 } @llvm.modf.ppcf128(ppc_fp128 %a)
+  %result.1 = extractvalue { ppc_fp128, ppc_fp128 } %result, 1
+  ret ppc_fp128 %result.1
+}
+
+define ppc_fp128 @test_modf_ppcf128_only_use_fractional(ppc_fp128 %a) {
+; CHECK-LABEL: test_modf_ppcf128_only_use_fractional:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    mflr r0
+; CHECK-NEXT:    stdu r1, -48(r1)
+; CHECK-NEXT:    std r0, 64(r1)
+; CHECK-NEXT:    .cfi_def_cfa_offset 48
+; CHECK-NEXT:    .cfi_offset lr, 16
+; CHECK-NEXT:    addi r5, r1, 32
+; CHECK-NEXT:    bl modfl
+; CHECK-NEXT:    nop
+; CHECK-NEXT:    addi r1, r1, 48
+; CHECK-NEXT:    ld r0, 16(r1)
+; CHECK-NEXT:    mtlr r0
+; CHECK-NEXT:    blr
+  %result = call { ppc_fp128, ppc_fp128 } @llvm.modf.ppcf128(ppc_fp128 %a)
+  %result.1 = extractvalue { ppc_fp128, ppc_fp128 } %result, 0
+  ret ppc_fp128 %result.1
+}
+
+define { ppc_fp128, ppc_fp128 } @test_modf_ppcf128_tail_call(ppc_fp128 %a) {
+; CHECK-LABEL: test_modf_ppcf128_tail_call:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    mflr r0
+; CHECK-NEXT:    stdu r1, -48(r1)
+; CHECK-NEXT:    std r0, 64(r1)
+; CHECK-NEXT:    .cfi_def_cfa_offset 48
+; CHECK-NEXT:    .cfi_offset lr, 16
+; CHECK-NEXT:    addi r5, r1, 32
+; CHECK-NEXT:    bl modfl
+; CHECK-NEXT:    nop
+; CHECK-NEXT:    lfd f3, 32(r1)
+; CHECK-NEXT:    lfd f4, 40(r1)
+; CHECK-NEXT:    addi r1, r1, 48
+; CHECK-NEXT:    ld r0, 16(r1)
+; CHECK-NEXT:    mtlr r0
+; CHECK-NEXT:    blr
+  %result = tail call { ppc_fp128, ppc_fp128 } @llvm.modf.ppcf128(ppc_fp128 %a)
+  ret { ppc_fp128, ppc_fp128 } %result
+}
+
+define ppc_fp128 @test_modf_ppcf128_only_use_intergral_tail_call(ppc_fp128 %a) {
+; CHECK-LABEL: test_modf_ppcf128_only_use_intergral_tail_call:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    mflr r0
+; CHECK-NEXT:    stdu r1, -48(r1)
+; CHECK-NEXT:    std r0, 64(r1)
+; CHECK-NEXT:    .cfi_def_cfa_offset 48
+; CHECK-NEXT:    .cfi_offset lr, 16
+; CHECK-NEXT:    addi r5, r1, 32
+; CHECK-NEXT:    bl modfl
+; CHECK-NEXT:    nop
+; CHECK-NEXT:    lfd f1, 32(r1)
+; CHECK-NEXT:    lfd f2, 40(r1)
+; CHECK-NEXT:    addi r1, r1, 48
+; CHECK-NEXT:    ld r0, 16(r1)
+; CHECK-NEXT:    mtlr r0
+; CHECK-NEXT:    blr
+  %result = tail call { ppc_fp128, ppc_fp128 } @llvm.modf.ppcf128(ppc_fp128 %a)
+  %result.1 = extractvalue { ppc_fp128, ppc_fp128 } %result, 1
+  ret ppc_fp128 %result.1
+}
+
+define ppc_fp128 @test_modf_ppcf128_only_use_fractional_tail_call(ppc_fp128 %a) {
+; CHECK-LABEL: test_modf_ppcf128_only_use_fractional_tail_call:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    mflr r0
+; CHECK-NEXT:    stdu r1, -48(r1)
+; CHECK-NEXT:    std r0, 64(r1)
+; CHECK-NEXT:    .cfi_def_cfa_offset 48
+; CHECK-NEXT:    .cfi_offset lr, 16
+; CHECK-NEXT:    addi r5, r1, 32
+; CHECK-NEXT:    bl modfl
+; CHECK-NEXT:    nop
+; CHECK-NEXT:    addi r1, r1, 48
+; CHECK-NEXT:    ld r0, 16(r1)
+; CHECK-NEXT:    mtlr r0
+; CHECK-NEXT:    blr
+  %result = tail call { ppc_fp128, ppc_fp128 } @llvm.modf.ppcf128(ppc_fp128 %a)
+  %result.1 = extractvalue { ppc_fp128, ppc_fp128 } %result, 0
+  ret ppc_fp128 %result.1
+}