[Hexagon] Add missing pattern for v8i1 type

HexagonISD::PFALSE and PTRUE patterns do not form independently in
general as they are treated like operands of all 0s or all 1s.
Eg: i32 = transfer HEXAGONISD::PFALSE.
In this case, v8i1 = HEXAGONISD::PFALSE is formed independently without
accompanying opcode.

This patch adds a pattern to transfer all 0s or all 1s to a scalar
register and then use that register and this PFALSE/PTRUE opcode
to transfer to a predicate register like v8i1.

Author: quic-santdas

llvm/lib/Target/Hexagon/HexagonPatterns.td

@@ -108,6 +108,9 @@ def ptrue:  PatFrag<(ops), (HexagonPTRUE)>;
 def pfalse: PatFrag<(ops), (HexagonPFALSE)>;
 def pnot:   PatFrag<(ops node:$Pu), (xor node:$Pu, ptrue)>;
 
+def: Pat<(v8i1 (HexagonPFALSE)), (C2_tfrrp (A2_tfrsi (i32 0)))>;
+def: Pat<(v8i1 (HexagonPTRUE)), (C2_tfrrp (A2_tfrsi (i32 -1)))>;
+
 def valign: PatFrag<(ops node:$Vt, node:$Vs, node:$Ru),
                     (HexagonVALIGN node:$Vt, node:$Vs, node:$Ru)>;
 def valignaddr: PatFrag<(ops node:$Addr), (HexagonVALIGNADDR node:$Addr)>;

llvm/test/CodeGen/Hexagon/isel/isel-tfrrp.ll

@@ -0,0 +1,15 @@
+; Check if a C2_tfrrp instruction with constant i32 0 input is generated
+; The constant 0 is generated by a transfer immediate instruction.
+
+; RUN: llc -march=hexagon -debug-only=isel 2>&1 < %s - | FileCheck %s
+
+; CHECK: [[R0:%[0-9]+]]:intregs = A2_tfrsi 0
+; CHECK-NEXT: predregs = C2_tfrrp killed [[R0]]:intregs
+
+define void @test_false(i1 %0) {
+  %2 = insertelement <1024 x i1> zeroinitializer, i1 %0, i64 0
+  tail call void @llvm.masked.store.v1024f32.p0(<1024 x float> zeroinitializer, ptr null, i32 1, <1024 x i1> %2)
+  ret void
+}
+
+declare void @llvm.masked.store.v1024f32.p0(<1024 x float>, ptr nocapture, i32 immarg, <1024 x i1>)