[RISCV][GISel] Add G_ZEXT to RISCVInstructionSelector::selectZExtBits. (#115391)

Author: topperc

llvm/lib/Target/RISCV/GISel/RISCVInstructionSelector.cpp

@@ -288,6 +288,10 @@ RISCVInstructionSelector::selectZExtBits(MachineOperand &Root,
     return {{[=](MachineInstrBuilder &MIB) { MIB.addReg(RegX); }}};
   }
 
+  if (mi_match(RootReg, *MRI, m_GZExt(m_Reg(RegX))) &&
+      MRI->getType(RegX).getScalarSizeInBits() == Bits)
+    return {{[=](MachineInstrBuilder &MIB) { MIB.addReg(RegX); }}};
+
   unsigned Size = MRI->getType(RootReg).getScalarSizeInBits();
   if (KB->maskedValueIsZero(RootReg, APInt::getBitsSetFrom(Size, Bits)))
     return {{[=](MachineInstrBuilder &MIB) { MIB.add(Root); }}};

llvm/test/CodeGen/RISCV/GlobalISel/double-convert.ll

@@ -300,9 +300,7 @@ define signext i32 @fcvt_d_wu_demanded_bits(i32 signext %0, ptr %1) nounwind {
 ; RV64IFD-LABEL: fcvt_d_wu_demanded_bits:
 ; RV64IFD:       # %bb.0:
 ; RV64IFD-NEXT:    addiw a0, a0, 1
-; RV64IFD-NEXT:    slli a2, a0, 32
-; RV64IFD-NEXT:    srli a2, a2, 32
-; RV64IFD-NEXT:    fcvt.d.wu fa5, a2
+; RV64IFD-NEXT:    fcvt.d.wu fa5, a0
 ; RV64IFD-NEXT:    fsd fa5, 0(a1)
 ; RV64IFD-NEXT:    ret
   %3 = add i32 %0, 1

llvm/test/CodeGen/RISCV/GlobalISel/float-convert.ll

@@ -272,9 +272,7 @@ define signext i32 @fcvt_s_wu_demanded_bits(i32 signext %0, ptr %1) nounwind {
 ; RV64IF-LABEL: fcvt_s_wu_demanded_bits:
 ; RV64IF:       # %bb.0:
 ; RV64IF-NEXT:    addiw a0, a0, 1
-; RV64IF-NEXT:    slli a2, a0, 32
-; RV64IF-NEXT:    srli a2, a2, 32
-; RV64IF-NEXT:    fcvt.s.wu fa5, a2
+; RV64IF-NEXT:    fcvt.s.wu fa5, a0
 ; RV64IF-NEXT:    fsw fa5, 0(a1)
 ; RV64IF-NEXT:    ret
   %3 = add i32 %0, 1