[FastISel] Add support for ptrtoaddr

Handle it the same as ptrtoint. For ptrtoaddr the resulting integer
size is guaranteed to match the address size. For the case where
address size and pointer size match, this will be a no-op. For the
case where the address size is smaller than the pointer size, this
will be a truncate (but this is not testable with in-tree targets).

Author: nikic

llvm/lib/CodeGen/SelectionDAG/FastISel.cpp

@@ -1843,7 +1843,8 @@ bool FastISel::selectOperator(const User *I, unsigned Opcode) {
     return selectCast(I, ISD::SINT_TO_FP);
 
   case Instruction::IntToPtr: // Deliberate fall-through.
-  case Instruction::PtrToInt: {
+  case Instruction::PtrToInt:
+  case Instruction::PtrToAddr: {
     EVT SrcVT = TLI.getValueType(DL, I->getOperand(0)->getType());
     EVT DstVT = TLI.getValueType(DL, I->getType());
     if (DstVT.bitsGT(SrcVT))

llvm/test/CodeGen/X86/ptrtoaddr-fast-isel.ll

@@ -0,0 +1,11 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=x86_64-linux-gnu -fast-isel -fast-isel-abort=1 < %s -o - | FileCheck %s
+
+define i64 @ptrtoaddr(ptr %p) {
+; CHECK-LABEL: ptrtoaddr:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    movq %rdi, %rax
+; CHECK-NEXT:    retq
+  %addr = ptrtoaddr ptr %p to i64
+  ret i64 %addr
+}