[RISCV][GISel] Make register bank selection for unary and binary arithmetic ops more generic. (#87593)

This is inspired by AArch64's getSameKindOfOperandsMapping, but based on
what RISC-V currently needs.

This removes the special vector case for G_ADD/SUB and unifies integer
and FP operations into the same handler.

G_SEXTLOAD/ZEXTLOAD have been separated from integer since they should
only be scalar integer and never vector.

Author: topperc

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

@@ -290,16 +290,7 @@ RISCVRegisterBankInfo::getInstrMapping(const MachineInstr &MI) const {
 
   switch (Opc) {
   case TargetOpcode::G_ADD:
-  case TargetOpcode::G_SUB: {
-    if (MRI.getType(MI.getOperand(0).getReg()).isVector()) {
-      LLT Ty = MRI.getType(MI.getOperand(0).getReg());
-      return getInstructionMapping(
-          DefaultMappingID, /*Cost=*/1,
-          getVRBValueMapping(Ty.getSizeInBits().getKnownMinValue()),
-          NumOperands);
-    }
-  }
-    LLVM_FALLTHROUGH;
+  case TargetOpcode::G_SUB:
   case TargetOpcode::G_SHL:
   case TargetOpcode::G_ASHR:
   case TargetOpcode::G_LSHR:
@@ -320,10 +311,6 @@ RISCVRegisterBankInfo::getInstrMapping(const MachineInstr &MI) const {
   case TargetOpcode::G_PTR_ADD:
   case TargetOpcode::G_PTRTOINT:
   case TargetOpcode::G_INTTOPTR:
-  case TargetOpcode::G_SEXTLOAD:
-  case TargetOpcode::G_ZEXTLOAD:
-    return getInstructionMapping(DefaultMappingID, /*Cost=*/1, GPRValueMapping,
-                                 NumOperands);
   case TargetOpcode::G_FADD:
   case TargetOpcode::G_FSUB:
   case TargetOpcode::G_FMUL:
@@ -334,10 +321,34 @@ RISCVRegisterBankInfo::getInstrMapping(const MachineInstr &MI) const {
   case TargetOpcode::G_FMAXNUM:
   case TargetOpcode::G_FMINNUM: {
     LLT Ty = MRI.getType(MI.getOperand(0).getReg());
-    return getInstructionMapping(DefaultMappingID, /*Cost=*/1,
-                                 getFPValueMapping(Ty.getSizeInBits()),
-                                 NumOperands);
+    TypeSize Size = Ty.getSizeInBits();
+
+    const ValueMapping *Mapping;
+    if (Ty.isVector())
+      Mapping = getVRBValueMapping(Size.getKnownMinValue());
+    else if (isPreISelGenericFloatingPointOpcode(Opc))
+      Mapping = getFPValueMapping(Size.getFixedValue());
+    else
+      Mapping = GPRValueMapping;
+
+#ifndef NDEBUG
+    // Make sure all the operands are using similar size and type.
+    for (unsigned Idx = 1; Idx != NumOperands; ++Idx) {
+      LLT OpTy = MRI.getType(MI.getOperand(Idx).getReg());
+      assert(Ty.isVector() == OpTy.isVector() &&
+             "Operand has incompatible type");
+      // Don't check size for GPR.
+      if (OpTy.isVector() || isPreISelGenericFloatingPointOpcode(Opc))
+        assert(Size == OpTy.getSizeInBits() && "Operand has incompatible size");
+    }
+#endif // End NDEBUG
+
+    return getInstructionMapping(DefaultMappingID, 1, Mapping, NumOperands);
   }
+  case TargetOpcode::G_SEXTLOAD:
+  case TargetOpcode::G_ZEXTLOAD:
+    return getInstructionMapping(DefaultMappingID, /*Cost=*/1, GPRValueMapping,
+                                 NumOperands);
   case TargetOpcode::G_IMPLICIT_DEF: {
     Register Dst = MI.getOperand(0).getReg();
     LLT DstTy = MRI.getType(Dst);