[PATCH] D116435: [RISCV] Generate 32 bits jumptable entries when code model is small

[Wang Pengcheng via Phabricator via llvm-commits]

pcwang-thead created this revision.
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The code can only address the whole RV32 address space or the lower 2 GiB
of the RV64 address space in small code model, so 32 bits entry is enough.
Cache hit ratio and code size have some improvements.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D116435

Files:
  llvm/lib/Target/RISCV/RISCVISelLowering.cpp
  llvm/lib/Target/RISCV/RISCVISelLowering.h
  llvm/test/CodeGen/RISCV/jumptable.ll


Index: llvm/test/CodeGen/RISCV/jumptable.ll
===================================================================
--- llvm/test/CodeGen/RISCV/jumptable.ll
+++ llvm/test/CodeGen/RISCV/jumptable.ll
@@ -239,11 +239,11 @@
 ; RV64I-SMALL-NEXT:    li a2, 5
 ; RV64I-SMALL-NEXT:    bltu a2, a0, .LBB1_9
 ; RV64I-SMALL-NEXT:  # %bb.1: # %entry
-; RV64I-SMALL-NEXT:    slli a0, a0, 3
+; RV64I-SMALL-NEXT:    slli a0, a0, 2
 ; RV64I-SMALL-NEXT:    lui a2, %hi(.LJTI1_0)
 ; RV64I-SMALL-NEXT:    addi a2, a2, %lo(.LJTI1_0)
 ; RV64I-SMALL-NEXT:    add a0, a0, a2
-; RV64I-SMALL-NEXT:    ld a0, 0(a0)
+; RV64I-SMALL-NEXT:    lw a0, 0(a0)
 ; RV64I-SMALL-NEXT:    jr a0
 ; RV64I-SMALL-NEXT:  .LBB1_2: # %bb1
 ; RV64I-SMALL-NEXT:    li a0, 4
Index: llvm/lib/Target/RISCV/RISCVISelLowering.h
===================================================================
--- llvm/lib/Target/RISCV/RISCVISelLowering.h
+++ llvm/lib/Target/RISCV/RISCVISelLowering.h
@@ -526,6 +526,13 @@
 
   bool shouldConvertFpToSat(unsigned Op, EVT FPVT, EVT VT) const override;
 
+  unsigned getJumpTableEncoding() const override;
+
+  const MCExpr *LowerCustomJumpTableEntry(const MachineJumpTableInfo *MJTI,
+                                          const MachineBasicBlock *MBB,
+                                          unsigned uid,
+                                          MCContext &Ctx) const override;
+
 private:
   /// RISCVCCAssignFn - This target-specific function extends the default
   /// CCValAssign with additional information used to lower RISC-V calling
Index: llvm/lib/Target/RISCV/RISCVISelLowering.cpp
===================================================================
--- llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -24,6 +24,7 @@
 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineJumpTableInfo.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/CodeGen/TargetLoweringObjectFileImpl.h"
 #include "llvm/CodeGen/ValueTypes.h"
@@ -10092,6 +10093,24 @@
   }
 }
 
+unsigned RISCVTargetLowering::getJumpTableEncoding() const {
+  // If we are using the small code model, we can reduce size of jump table
+  // entry to 4 bytes.
+  if (!isPositionIndependent() &&
+      getTargetMachine().getCodeModel() == CodeModel::Small) {
+    return MachineJumpTableInfo::EK_Custom32;
+  }
+  return TargetLowering::getJumpTableEncoding();
+}
+
+const MCExpr *RISCVTargetLowering::LowerCustomJumpTableEntry(
+    const MachineJumpTableInfo *MJTI, const MachineBasicBlock *MBB,
+    unsigned uid, MCContext &Ctx) const {
+  assert(!isPositionIndependent() &&
+         getTargetMachine().getCodeModel() == CodeModel::Small);
+  return MCSymbolRefExpr::create(MBB->getSymbol(), Ctx);
+}
+
 bool RISCVTargetLowering::isFMAFasterThanFMulAndFAdd(const MachineFunction &MF,
                                                      EVT VT) const {
   VT = VT.getScalarType();


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