[RISCV] Add zext.h/zext.w to RISCVTTIImpl::getIntImmCostInst.

[craig.topper]

Summary

If we have these instructions, we don't need to hoist the immediate
for an AND that would match them.

[luismarques]

LGTM.

llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp

InstructionCost RISCVTTIImpl::getIntImmCostInst(unsigned Opcode, unsigned Idx,
   unsigned ImmArgIdx = ~0U;
 
   switch (Opcode) {
   case Instruction::GetElementPtr:
     // Never hoist any arguments to a GetElementPtr. CodeGenPrepare will
     // split up large offsets in GEP into better parts than ConstantHoisting
     // can.
     return TTI::TCC_Free;
-  case Instruction::Add:
   case Instruction::And:
+    // zext.h
+    if (Imm == UINT64_C(0xffff) && ST->hasStdExtZbb())
+      return TTI::TCC_Free;
+    // zext.w
+    if (Imm == UINT64_C(0xffffffff) && ST->hasStdExtZbb())
+      return TTI::TCC_Free;
+    LLVM_FALLTHROUGH;
+  case Instruction::Add:
   case Instruction::Or:
   case Instruction::Xor:
   case Instruction::Mul:
     Takes12BitImm = true;
     break;
   case Instruction::Sub:
   case Instruction::Shl:
   case Instruction::LShr:

llvm/test/Transforms/ConstantHoisting/RISCV/immediates.ll

 ; Check that we hoist immediates with very large values.
 define i128 @test4(i128 %a) nounwind {
 ; CHECK-LABEL: test4
 ; CHECK: %const = bitcast i128 12297829382473034410122878 to i128
   %1 = add i128 %a, 12297829382473034410122878
   %2 = add i128 %1, 12297829382473034410122878
   ret i128 %2
 }
+
+; Check that we hoist zext.h without Zbb.
+define i32 @test5(i32 %a) nounwind {
+; CHECK-LABEL: test5
+; CHECK: %const = bitcast i32 65535 to i32
+  %1 = and i32 %a, 65535
+  %2 = and i32 %1, 65535
+  ret i32 %2
+}
+
+; Check that we don't hoist zext.h with 65535 with Zbb.
+define i32 @test6(i32 %a) nounwind "target-features"="+experimental-zbb" {
+; CHECK-LABEL: test6
+; CHECK: and i32 %a, 65535
+  %1 = and i32 %a, 65535
+  %2 = and i32 %1, 65535
+  ret i32 %2
+}
+
+; Check that we hoist zext.w without Zba.
+define i64 @test7(i64 %a) nounwind {
+; CHECK-LABEL: test7
+; CHECK: %const = bitcast i64 4294967295 to i64
+  %1 = and i64 %a, 4294967295
+  %2 = and i64 %1, 4294967295
+  ret i64 %2
+}
+
+; Check that we don't hoist zext.w with Zba.
+define i64 @test8(i64 %a) nounwind "target-features"="+experimental-zbb" {
+; CHECK-LABEL: test8
+; CHECK: and i64 %a, 4294967295
+  %1 = and i64 %a, 4294967295
+  %2 = and i64 %1, 4294967295
+  ret i64 %2
+}