[RISCV] Implement isTruncateFree

Adapted from ARM's implementation introduced in r313533 and r314280.

llvm-svn: 330940

2 files changed, 22 insertions, 0 deletions

diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index 16b4bddcd5c..d1ad453fbf8 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -191,6 +191,26 @@ bool RISCVTargetLowering::isLegalAddImmediate(int64_t Imm) const {
   return isInt<12>(Imm);
 }
 
+// On RV32, 64-bit integers are split into their high and low parts and held
+// in two different registers, so the trunc is free since the low register can
+// just be used.
+bool RISCVTargetLowering::isTruncateFree(Type *SrcTy, Type *DstTy) const {
+  if (Subtarget.is64Bit() || !SrcTy->isIntegerTy() || !DstTy->isIntegerTy())
+    return false;
+  unsigned SrcBits = SrcTy->getPrimitiveSizeInBits();
+  unsigned DestBits = DstTy->getPrimitiveSizeInBits();
+  return (SrcBits == 64 && DestBits == 32);
+}
+
+bool RISCVTargetLowering::isTruncateFree(EVT SrcVT, EVT DstVT) const {
+  if (Subtarget.is64Bit() || SrcVT.isVector() || DstVT.isVector() ||
+      !SrcVT.isInteger() || !DstVT.isInteger())
+    return false;
+  unsigned SrcBits = SrcVT.getSizeInBits();
+  unsigned DestBits = DstVT.getSizeInBits();
+  return (SrcBits == 64 && DestBits == 32);
+}
+
 // Changes the condition code and swaps operands if necessary, so the SetCC
 // operation matches one of the comparisons supported directly in the RISC-V
 // ISA.
diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.h b/llvm/lib/Target/RISCV/RISCVISelLowering.h
index dccd0315bbf..2a2016ef5f5 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.h
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.h
@@ -44,6 +44,8 @@ public:
                              Instruction *I = nullptr) const override;
   bool isLegalICmpImmediate(int64_t Imm) const override;
   bool isLegalAddImmediate(int64_t Imm) const override;
+  bool isTruncateFree(Type *SrcTy, Type *DstTy) const override;
+  bool isTruncateFree(EVT SrcVT, EVT DstVT) const override;
 
   // Provide custom lowering hooks for some operations.
   SDValue LowerOperation(SDValue Op, SelectionDAG &DAG) const override;