Add trunc (select c, a, b) -> select c (trunc a), (trunc b) combine.

[arsenm]

Summary

Do this if the truncate is free and the select is legal.

[arsenm]

r212640

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

if (isa<ConstantSDNode>(EltNo) && isTypeLegal(NVT)) {
                               NVT, N0.getOperand(0));
 
       return DAG.getNode(ISD::EXTRACT_VECTOR_ELT,
                          SDLoc(N), TrTy, V,
                          DAG.getConstant(Index, IndexTy));
     }
   }
 
+  // trunc (select c, a, b) -> select c, (trunc a), (trunc b)
+  if (N0.getOpcode() == ISD::SELECT) {
+    EVT SrcVT = N0.getValueType();
+    if ((!LegalOperations || TLI.isOperationLegal(ISD::SELECT, SrcVT)) &&
+        TLI.isTruncateFree(SrcVT, VT)) {
+      SDLoc SL(N0);
+      SDValue TruncOp0 = DAG.getNode(ISD::TRUNCATE, SL, VT, N0.getOperand(1));
+      SDValue TruncOp1 = DAG.getNode(ISD::TRUNCATE, SL, VT, N0.getOperand(2));
+      EVT SetCCVT = getSetCCResultType(VT);
+      SDValue Cond = DAG.getSExtOrTrunc(N0.getOperand(0), SL, SetCCVT);
+      return DAG.getNode(ISD::SELECT, SDLoc(N), VT, Cond, TruncOp0, TruncOp1);
+    }
+  }
+
   // Fold a series of buildvector, bitcast, and truncate if possible.
   // For example fold
   //   (2xi32 trunc (bitcast ((4xi32)buildvector x, x, y, y) 2xi64)) to
   //   (2xi32 (buildvector x, y)).
   if (Level == AfterLegalizeVectorOps && VT.isVector() &&
       N0.getOpcode() == ISD::BITCAST && N0.hasOneUse() &&
       N0.getOperand(0).getOpcode() == ISD::BUILD_VECTOR &&
       N0.getOperand(0).hasOneUse()) {

test/CodeGen/R600/select64.ll

 ; RUN: llc < %s -march=r600 -mcpu=SI -verify-machineinstrs | FileCheck %s
 
 ; CHECK-LABEL: @select0
 ; i64 select should be split into two i32 selects, and we shouldn't need
 ; to use a shfit to extract the hi dword of the input.
 ; CHECK-NOT: S_LSHR_B64
 ; CHECK: V_CNDMASK
 ; CHECK: V_CNDMASK
 define void @select0(i64 addrspace(1)* %out, i32 %cond, i64 %in) {
 entry:
   %0 = icmp ugt i32 %cond, 5
   %1 = select i1 %0, i64 0, i64 %in
   store i64 %1, i64 addrspace(1)* %out
   ret void
 }
+
+; CHECK-LABEL: @select_trunc_i64
+; CHECK: V_CNDMASK_B32
+; CHECK-NOT: V_CNDMASK_B32
+define void @select_trunc_i64(i32 addrspace(1)* %out, i32 %cond, i64 %in) nounwind {
+  %cmp = icmp ugt i32 %cond, 5
+  %sel = select i1 %cmp, i64 0, i64 %in
+  %trunc = trunc i64 %sel to i32
+  store i32 %trunc, i32 addrspace(1)* %out, align 4
+  ret void
+}
+
+; CHECK-LABEL: @select_trunc_i64_2
+; CHECK: V_CNDMASK_B32
+; CHECK-NOT: V_CNDMASK_B32
+define void @select_trunc_i64_2(i32 addrspace(1)* %out, i32 %cond, i64 %a, i64 %b) nounwind {
+  %cmp = icmp ugt i32 %cond, 5
+  %sel = select i1 %cmp, i64 %a, i64 %b
+  %trunc = trunc i64 %sel to i32
+  store i32 %trunc, i32 addrspace(1)* %out, align 4
+  ret void
+}
+
+; CHECK-LABEL: @v_select_trunc_i64_2
+; CHECK: V_CNDMASK_B32
+; CHECK-NOT: V_CNDMASK_B32
+define void @v_select_trunc_i64_2(i32 addrspace(1)* %out, i32 %cond, i64 addrspace(1)* %aptr, i64 addrspace(1)* %bptr) nounwind {
+  %cmp = icmp ugt i32 %cond, 5
+  %a = load i64 addrspace(1)* %aptr, align 8
+  %b = load i64 addrspace(1)* %bptr, align 8
+  %sel = select i1 %cmp, i64 %a, i64 %b
+  %trunc = trunc i64 %sel to i32
+  store i32 %trunc, i32 addrspace(1)* %out, align 4
+  ret void
+}

test/CodeGen/X86/shift-parts.ll

-; RUN: llc < %s -march=x86-64 | grep shrdq
+; RUN: llc -march=x86-64 < %s | FileCheck %s
 ; PR4736
 
 %0 = type { i32, i8, [35 x i8] }
 
 @g_144 = external global %0, align 8              ; <%0*> [#uses=1]
 
-define i32 @int87(i32 %uint64p_8) nounwind {
+; CHECK: shrdq
+
+define i32 @int87(i32 %uint64p_8, i1 %cond) nounwind {
 entry:
   %srcval4 = load i320* bitcast (%0* @g_144 to i320*), align 8 ; <i320> [#uses=1]
   br label %for.cond
 
 for.cond:                                         ; preds = %for.cond, %entry
-  %call3.in.in.in.v = select i1 undef, i320 192, i320 128 ; <i320> [#uses=1]
+  %call3.in.in.in.v = select i1 %cond, i320 192, i320 128 ; <i320> [#uses=1]
   %call3.in.in.in = lshr i320 %srcval4, %call3.in.in.in.v ; <i320> [#uses=1]
   %call3.in = trunc i320 %call3.in.in.in to i32   ; <i32> [#uses=1]
   %tobool = icmp eq i32 %call3.in, 0              ; <i1> [#uses=1]
   br i1 %tobool, label %for.cond, label %if.then
 
 if.then:                                          ; preds = %for.cond
   ret i32 1
 }