[DAG] Add constant SPLAT handling in getNodes SIGN_EXTEND_INREG

This helps simplify constant splats a little. Without this the code in
llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp#L14072 always returns the
existing node.

Differential Revision: https://reviews.llvm.org/D157259

Author: davemgreen

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -6592,6 +6592,13 @@ SDValue SelectionDAG::getNode(unsigned Opcode, const SDLoc &DL, EVT VT,
       }
       return getBuildVector(VT, DL, Ops);
     }
+
+    if (N1.getOpcode() == ISD::SPLAT_VECTOR &&
+        isa<ConstantSDNode>(N1.getOperand(0)))
+      return getNode(
+          ISD::SPLAT_VECTOR, DL, VT,
+          SignExtendInReg(N1.getConstantOperandAPInt(0),
+                          N1.getOperand(0).getValueType()));
     break;
   }
   case ISD::FP_TO_SINT_SAT:

llvm/test/CodeGen/AArch64/sve-fp-int-min-max.ll

@@ -6,21 +6,17 @@ define i64 @scalable_int_min_max(ptr %arg, ptr %arg1, <vscale x 2 x ptr> %i37, <
 ; CHECK:       // %bb.0: // %entry
 ; CHECK-NEXT:    ptrue p0.d
 ; CHECK-NEXT:    mov w8, #3745 // =0xea1
-; CHECK-NEXT:    movk w8, #16618, lsl #16
 ; CHECK-NEXT:    ld1w { z3.d }, p0/z, [x0]
+; CHECK-NEXT:    movk w8, #16618, lsl #16
 ; CHECK-NEXT:    mov w9, #57344 // =0xe000
-; CHECK-NEXT:    mov z6.d, #1023 // =0x3ff
 ; CHECK-NEXT:    movk w9, #17535, lsl #16
 ; CHECK-NEXT:    mov z4.s, w8
 ; CHECK-NEXT:    fmul z4.s, p0/m, z4.s, z3.s
 ; CHECK-NEXT:    mov z5.s, w9
 ; CHECK-NEXT:    fadd z4.s, p0/m, z4.s, z5.s
-; CHECK-NEXT:    mov z5.d, #0 // =0x0
+; CHECK-NEXT:    mov z5.d, #1023 // =0x3ff
 ; CHECK-NEXT:    fcvtzs z4.d, p0/m, z4.s
-; CHECK-NEXT:    sxtw z5.d, p0/m, z5.d
-; CHECK-NEXT:    smax z4.d, p0/m, z4.d, z5.d
-; CHECK-NEXT:    movprfx z5, z6
-; CHECK-NEXT:    sxtw z5.d, p0/m, z6.d
+; CHECK-NEXT:    smax z4.d, z4.d, #0
 ; CHECK-NEXT:    smin z4.d, p0/m, z4.d, z5.d
 ; CHECK-NEXT:    cmpne p1.d, p0/z, z4.d, #0
 ; CHECK-NEXT:    ld1w { z4.d }, p1/z, [x1]

llvm/test/CodeGen/AArch64/sve-splat-sext.ll

@@ -0,0 +1,40 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -O2 -mtriple=aarch64-linux-gnu -mattr=+sve < %s | FileCheck %s
+
+define <vscale x 8 x i16> @sext_splat_v8i16_128() {
+; CHECK-LABEL: sext_splat_v8i16_128:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    mov z0.h, #-128 // =0xffffffffffffff80
+; CHECK-NEXT:    ret
+  %i = insertelement <vscale x 8 x i16> poison, i16 128, i32 0
+  %s = shufflevector <vscale x 8 x i16> %i, <vscale x 8 x i16> poison, <vscale x 8 x i32> zeroinitializer
+  %a = shl <vscale x 8 x i16> %s, shufflevector (<vscale x 8 x i16> insertelement(<vscale x 8 x i16> undef, i16 8, i32 0), <vscale x 8 x i16> undef, <vscale x 8 x i32> zeroinitializer)
+  %b = ashr <vscale x 8 x i16> %a, shufflevector (<vscale x 8 x i16> insertelement(<vscale x 8 x i16> undef, i16 8, i32 0), <vscale x 8 x i16> undef, <vscale x 8 x i32> zeroinitializer)
+  ret <vscale x 8 x i16> %b
+}
+
+define <vscale x 8 x i1> @sext_icmp_splat_v8i16_128(<vscale x 8 x i8> %d) {
+; CHECK-LABEL: sext_icmp_splat_v8i16_128:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    ptrue p0.h
+; CHECK-NEXT:    sxtb z0.h, p0/m, z0.h
+; CHECK-NEXT:    cmpgt p0.h, p0/z, z0.h, #-1
+; CHECK-NEXT:    ret
+  %i = insertelement <vscale x 8 x i8> poison, i8 128, i32 0
+  %s = shufflevector <vscale x 8 x i8> %i, <vscale x 8 x i8> poison, <vscale x 8 x i32> zeroinitializer
+  %c = icmp ugt <vscale x 8 x i8> %s, %d
+  ret <vscale x 8 x i1> %c
+}
+
+define <vscale x 4 x i1> @sext_icmp_splat_v4i16_128(<vscale x 4 x i8> %d) {
+; CHECK-LABEL: sext_icmp_splat_v4i16_128:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    ptrue p0.s
+; CHECK-NEXT:    sxtb z0.s, p0/m, z0.s
+; CHECK-NEXT:    cmpgt p0.s, p0/z, z0.s, #-1
+; CHECK-NEXT:    ret
+  %i = insertelement <vscale x 4 x i8> poison, i8 128, i32 0
+  %s = shufflevector <vscale x 4 x i8> %i, <vscale x 4 x i8> poison, <vscale x 4 x i32> zeroinitializer
+  %c = icmp ugt <vscale x 4 x i8> %s, %d
+  ret <vscale x 4 x i1> %c
+}