[PowerPC] Fix parest build failure in SPEC2017.

[jtony]

Summary

The build failure was caused by an assertion in pre-legalization DAGCombine:

llc: /home/jtony/src/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp:7232: void llvm::SelectionDAG::ReplaceAllUsesWith(llvm::SDNode*, llvm::SDNode*): Assertion `(!From->hasAnyUseOfValue(i) || From->getValueType(i) == To->getValueType(i)) && "Cannot use this version of ReplaceAllUsesWith!"' failed.

When it crashes, it is trying to do the following:

Combining: t6: ppcf128 = uint_to_fp t5
        ... into: t20: f32 = PPCISD::FCFIDUS t19

which is clearly wrong since ppcf128 are definitely different type with f32 and we cannot change the node value type when do DAGCombine. The fix is don't handle ppc_fp128 or i1 conversions in PPCTargetLowering::combineFPToIntToFP and leave it to downstream to legalize it and expand it to small legal types.

Tested with 3-stage bootstrap and LNT and SPEC2017, they are functionally clean.

[hfinkel]

LGTM

lib/Target/PowerPC/PPCISelLowering.cpp

SDValue PPCTargetLowering::combineFPToIntToFP(SDNode *N,
 
   if (useSoftFloat() || !Subtarget.has64BitSupport())
     return SDValue();
 
   SelectionDAG &DAG = DCI.DAG;
   SDLoc dl(N);
   SDValue Op(N, 0);
 
+  // Don't handle ppc_fp128 here or i1 conversions.
+  if (Op.getValueType() != MVT::f32 && Op.getValueType() != MVT::f64)
+    return SDValue();
+  if (Op.getOperand(0).getValueType() == MVT::i1)
+    return SDValue();
+
   SDValue FirstOperand(Op.getOperand(0));
   bool SubWordLoad = FirstOperand.getOpcode() == ISD::LOAD &&
     (FirstOperand.getValueType() == MVT::i8 ||
      FirstOperand.getValueType() == MVT::i16);
   if (Subtarget.hasP9Vector() && Subtarget.hasP9Altivec() && SubWordLoad) {
     bool Signed = N->getOpcode() == ISD::SINT_TO_FP;
     bool DstDouble = Op.getValueType() == MVT::f64;
     unsigned ConvOp = Signed ?
if (Subtarget.hasP9Vector() && Subtarget.hasP9Altivec() && SubWordLoad) {
     if (Signed) {
       SDValue ExtOps[] = { Ld, WidthConst };
       SDValue Ext = DAG.getNode(PPCISD::VEXTS, dl, MVT::f64, ExtOps);
       return DAG.getNode(ConvOp, dl, DstDouble ? MVT::f64 : MVT::f32, Ext);
     } else
       return DAG.getNode(ConvOp, dl, DstDouble ? MVT::f64 : MVT::f32, Ld);
   }
 
-  // Don't handle ppc_fp128 here or i1 conversions.
-  if (Op.getValueType() != MVT::f32 && Op.getValueType() != MVT::f64)
-    return SDValue();
-  if (Op.getOperand(0).getValueType() == MVT::i1)
-    return SDValue();
 
   // For i32 intermediate values, unfortunately, the conversion functions
   // leave the upper 32 bits of the value are undefined. Within the set of
   // scalar instructions, we have no method for zero- or sign-extending the
   // value. Thus, we cannot handle i32 intermediate values here.
   if (Op.getOperand(0).getValueType() == MVT::i32)
     return SDValue();
 

test/CodeGen/PowerPC/uint-to-ppcfp128-crash.ll

+; RUN: llc -verify-machineinstrs -mcpu=pwr9 \
+; RUN:   -mtriple=powerpc64le-unknown-linux-gnu < %s | FileCheck %s
+
+; Ensure we don't crash by trying to convert directly from a subword load
+; to a ppc_fp128 as we do for conversions to f32/f64.
+define ppc_fp128 @test(i16* nocapture readonly %Ptr) {
+entry:
+  %0 = load i16, i16* %Ptr, align 2
+  %conv = uitofp i16 %0 to ppc_fp128
+  ret ppc_fp128 %conv
+; CHECK: lhz [[LD:[0-9]+]], 0(3)
+; CHECK: mtvsrwa [[MV:[0-9]+]], [[LD]]
+; CHECK: xscvsxddp [[CONV:[0-9]+]], [[MV]]
+; CHECK: bl __gcc_qadd
+}