[LegalizeVectorTypes][X86][ARM][AArch64][PowerPC] Don't use SplitVecOp_TruncateHelper for FP_TO_SINT/UINT.

SplitVecOp_TruncateHelper tries to promote the result type while splitting FP_TO_SINT/UINT. It then concatenates the result and introduces a truncate to the original result type. But it does this without inserting the AssertZExt/AssertSExt that the regular result type promotion would insert. Nor does it turn FP_TO_UINT into FP_TO_SINT the way normal result type promotion for these operations does. This is bad on X86 which doesn't support FP_TO_SINT until AVX512.

This patch disables the use of SplitVecOp_TruncateHelper for these operations and just lets normal promotion handle it. I've tweaked a couple things in X86ISelLowering to avoid a few obvious regressions there. I believe all the changes on X86 are improvements. The other targets look neutral.

Differential Revision: https://reviews.llvm.org/D54906

llvm-svn: 347593

1 files changed, 2 insertions, 7 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeVectorTypes.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeVectorTypes.cpp
index f34f01cb9fb..2809fcaff4f 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeVectorTypes.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeVectorTypes.cpp
@@ -1694,13 +1694,6 @@ bool DAGTypeLegalizer::SplitVectorOperand(SDNode *N, unsigned OpNo) {
     case ISD::VSELECT:
       Res = SplitVecOp_VSELECT(N, OpNo);
       break;
-    case ISD::FP_TO_SINT:
-    case ISD::FP_TO_UINT:
-      if (N->getValueType(0).bitsLT(N->getOperand(0).getValueType()))
-        Res = SplitVecOp_TruncateHelper(N);
-      else
-        Res = SplitVecOp_UnaryOp(N);
-      break;
     case ISD::SINT_TO_FP:
     case ISD::UINT_TO_FP:
       if (N->getValueType(0).bitsLT(N->getOperand(0).getValueType()))
@@ -1708,6 +1701,8 @@ bool DAGTypeLegalizer::SplitVectorOperand(SDNode *N, unsigned OpNo) {
       else
         Res = SplitVecOp_UnaryOp(N);
       break;
+    case ISD::FP_TO_SINT:
+    case ISD::FP_TO_UINT:
     case ISD::CTTZ:
     case ISD::CTLZ:
     case ISD::CTPOP: