0076-RISCV-Implement-isZExtFree.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Alex Bradbury <asb@lowrisc.org>
Subject: [RISCV] Implement isZExtFree

Returns true if it's a load, where we know LBU/LHU/LWU will be selected. Saves
a number of unnecessary zexts across the torture suite.
---
 lib/Target/RISCV/RISCVISelLowering.cpp | 14 ++++++++++++++
 lib/Target/RISCV/RISCVISelLowering.h   |  1 +
 2 files changed, 15 insertions(+)

diff --git a/lib/Target/RISCV/RISCVISelLowering.cpp b/lib/Target/RISCV/RISCVISelLowering.cpp
index c60b4abc2c8..adf0d0c70ab 100644
--- a/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -201,6 +201,20 @@ bool RISCVTargetLowering::isTruncateFree(EVT SrcVT, EVT DstVT) const {
   return (SrcBits == 64 && DestBits == 32);
 }
 
+bool RISCVTargetLowering::isZExtFree(SDValue Val, EVT VT2) const {
+  // Zexts are free if they can be combined with a load.
+  if (auto *LD = dyn_cast<LoadSDNode>(Val)) {
+    EVT MemVT = LD->getMemoryVT();
+    if ((MemVT == MVT::i8 || MemVT == MVT::i16 ||
+         (Subtarget.is64Bit() && MemVT == MVT::i32)) &&
+        (LD->getExtensionType() == ISD::NON_EXTLOAD ||
+         LD->getExtensionType() == ISD::ZEXTLOAD))
+      return true;
+  }
+
+  return TargetLowering::isZExtFree(Val, VT2);
+}
+
 // 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/lib/Target/RISCV/RISCVISelLowering.h b/lib/Target/RISCV/RISCVISelLowering.h
index d6dfbf6625e..ccce434f69f 100644
--- a/lib/Target/RISCV/RISCVISelLowering.h
+++ b/lib/Target/RISCV/RISCVISelLowering.h
@@ -44,6 +44,7 @@ public:
   bool isLegalAddImmediate(int64_t Imm) const override;
   bool isTruncateFree(Type *SrcTy, Type *DstTy) const override;
   bool isTruncateFree(EVT SrcVT, EVT DstVT) const override;
+  bool isZExtFree(SDValue Val, EVT VT2) const override;
 
   // Provide custom lowering hooks for some operations.
   SDValue LowerOperation(SDValue Op, SelectionDAG &DAG) const override;
-- 
2.16.2