[RISCV] Codegen support for materializing constants

Differential Revision: https://reviews.llvm.org/D39101


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@317684 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 71 insertions, 1 deletions

diff --git a/lib/Target/RISCV/RISCVInstrInfo.td b/lib/Target/RISCV/RISCVInstrInfo.td
index 23adf1eda9d0..a19a636bdece 100644
--- a/lib/Target/RISCV/RISCVInstrInfo.td
+++ b/lib/Target/RISCV/RISCVInstrInfo.td
@@ -86,6 +86,24 @@ def simm21_lsb0 : Operand<XLenVT> {
   let DecoderMethod = "decodeSImmOperandAndLsl1<21>";
 }
 
+// Standalone (codegen-only) immleaf patterns.
+def simm32 : ImmLeaf<XLenVT, [{return isInt<32>(Imm);}]>;
+
+// Extract least significant 12 bits from an immediate value and sign extend
+// them.
+def LO12Sext : SDNodeXForm<imm, [{
+  return CurDAG->getTargetConstant(SignExtend64<12>(N->getZExtValue()),
+                                   SDLoc(N), N->getValueType(0));
+}]>;
+
+// Extract the most significant 20 bits from an immediate value. Add 1 if bit
+// 11 is 1, to compensate for the low 12 bits in the matching immediate addi
+// or ld/st being negative.
+def HI20 : SDNodeXForm<imm, [{
+  return CurDAG->getTargetConstant(((N->getZExtValue()+0x800) >> 12) & 0xfffff,
+                                   SDLoc(N), N->getValueType(0));
+}]>;
+
 //===----------------------------------------------------------------------===//
 // Instruction Class Templates
 //===----------------------------------------------------------------------===//
@@ -257,6 +275,12 @@ class PatGprUimm5<SDPatternOperator OpNode, RVInstIShift Inst>
     : Pat<(OpNode GPR:$rs1, uimm5:$shamt),
           (Inst GPR:$rs1, uimm5:$shamt)>;
 
+/// Immediates
+
+def : Pat<(simm12:$imm), (ADDI X0, simm12:$imm)>;
+// TODO: Add a pattern for immediates with all zeroes in the lower 12 bits.
+def : Pat<(simm32:$imm), (ADDI (LUI (HI20 imm:$imm)), (LO12Sext imm:$imm))>;
+
 /// Simple arithmetic operations
 
 def : PatGprGpr<add, ADD>;
diff --git a/test/CodeGen/RISCV/alu32.ll b/test/CodeGen/RISCV/alu32.ll
index 32242d2e40d3..9db6bb9dd434 100644
--- a/test/CodeGen/RISCV/alu32.ll
+++ b/test/CodeGen/RISCV/alu32.ll
@@ -7,7 +7,6 @@ define i32 @addi(i32 %a) nounwind {
 ; RV32I-LABEL: addi:
 ; RV32I: addi a0, a0, 1
 ; RV32I: jalr zero, ra, 0
-; TODO: check support for materialising larger constants
   %1 = add i32 %a, 1
   ret i32 %1
 }
diff --git a/test/CodeGen/RISCV/imm.ll b/test/CodeGen/RISCV/imm.ll
new file mode 100644
index 000000000000..c52638da02eb
--- /dev/null
+++ b/test/CodeGen/RISCV/imm.ll
@@ -0,0 +1,47 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=riscv32 -verify-machineinstrs < %s \
+; RUN:   | FileCheck %s -check-prefix=RV32I
+
+; Materializing constants
+
+define i32 @zero() nounwind {
+; RV32I-LABEL: zero:
+; RV32I:       # BB#0:
+; RV32I-NEXT:    addi a0, zero, 0
+; RV32I-NEXT:    jalr zero, ra, 0
+  ret i32 0
+}
+
+define i32 @pos_small() nounwind {
+; RV32I-LABEL: pos_small:
+; RV32I:       # BB#0:
+; RV32I-NEXT:    addi a0, zero, 2047
+; RV32I-NEXT:    jalr zero, ra, 0
+  ret i32 2047
+}
+
+define i32 @neg_small() nounwind {
+; RV32I-LABEL: neg_small:
+; RV32I:       # BB#0:
+; RV32I-NEXT:    addi a0, zero, -2048
+; RV32I-NEXT:    jalr zero, ra, 0
+  ret i32 -2048
+}
+
+define i32 @pos_i32() nounwind {
+; RV32I-LABEL: pos_i32:
+; RV32I:       # BB#0:
+; RV32I-NEXT:    lui a0, 423811
+; RV32I-NEXT:    addi a0, a0, -1297
+; RV32I-NEXT:    jalr zero, ra, 0
+  ret i32 1735928559
+}
+
+define i32 @neg_i32() nounwind {
+; RV32I-LABEL: neg_i32:
+; RV32I:       # BB#0:
+; RV32I-NEXT:    lui a0, 912092
+; RV32I-NEXT:    addi a0, a0, -273
+; RV32I-NEXT:    jalr zero, ra, 0
+  ret i32 -559038737
+}