[RISCV] Improve 64-bit integer constant materialization for more cases.

For positive constants we try shifting left to remove leading zeros
and fill the bottom bits with 1s. We then materialize that constant
shift it right.

This patch adds a new strategy to try filling the bottom bits with
zeros instead. This catches some additional cases.

lib/Target/RISCV/MCTargetDesc/RISCVMatInt.cpp

@@ -94,6 +94,16 @@ InstSeq generateInstSeq(int64_t Val, bool IsRV64) {
     generateInstSeqImpl(Val, IsRV64, TmpSeq);
     TmpSeq.push_back(RISCVMatInt::Inst(RISCV::SRLI, ShiftAmount));
 
+    // Keep the new sequence if it is an improvement.
+    if (TmpSeq.size() < Res.size())
+      Res = TmpSeq;
+
+    // Some cases can benefit from filling the lower bits with zeros instead.
+    Val &= maskTrailingZeros<uint64_t>(ShiftAmount);
+    TmpSeq.clear();
+    generateInstSeqImpl(Val, IsRV64, TmpSeq);
+    TmpSeq.push_back(RISCVMatInt::Inst(RISCV::SRLI, ShiftAmount));
+
     // Keep the new sequence if it is an improvement.
     if (TmpSeq.size() < Res.size())
       Res = TmpSeq;

test/CodeGen/RISCV/calling-conv-half.ll

@@ -347,10 +347,9 @@ define i32 @caller_half_on_stack() nounwind {
 ; RV64IF:       # %bb.0:
 ; RV64IF-NEXT:    addi sp, sp, -16
 ; RV64IF-NEXT:    sd ra, 8(sp) # 8-byte Folded Spill
-; RV64IF-NEXT:    lui a0, 256
+; RV64IF-NEXT:    addi a0, zero, -183
-; RV64IF-NEXT:    addiw a0, a0, -11
+; RV64IF-NEXT:    slli a0, a0, 40
-; RV64IF-NEXT:    slli a0, a0, 12
+; RV64IF-NEXT:    srli t0, a0, 32
-; RV64IF-NEXT:    addi t0, a0, -1792
 ; RV64IF-NEXT:    addi a0, zero, 1
 ; RV64IF-NEXT:    addi a1, zero, 2
 ; RV64IF-NEXT:    addi a2, zero, 3

test/CodeGen/RISCV/imm.ll

@@ -375,8 +375,7 @@ define i64 @imm_right_shifted_lui_1() nounwind {
 ;
 ; RV64I-LABEL: imm_right_shifted_lui_1:
 ; RV64I:       # %bb.0:
-; RV64I-NEXT:    lui a0, 983072
+; RV64I-NEXT:    lui a0, 983056
-; RV64I-NEXT:    addiw a0, a0, -1
 ; RV64I-NEXT:    srli a0, a0, 16
 ; RV64I-NEXT:    ret
   ret i64 281474976706561 ; 0xFFFF_FFFF_F001

test/MC/RISCV/rv64i-aliases-valid.s

@@ -118,8 +118,7 @@ li x5, 0x100004000
 # CHECK-EXPAND-NEXT: addiw t1, t1, 1
 # CHECK-EXPAND-NEXT: slli t1, t1, 32
 li x6, 0x100100000000
-# CHECK-EXPAND: lui t2, 983072
+# CHECK-EXPAND: lui t2, 983056
-# CHECK-EXPAND-NEXT: addiw t2, t2, -1
 # CHECK-EXPAND-NEXT: srli t2, t2, 16
 li x7, 0xFFFFFFFFF001
 # CHECK-EXPAND: lui s0, 65536