[IR] Handle trunc for ptrtoaddr(inttoptr) cast pair

llvm/lib/IR/Instructions.cpp

@@ -2965,19 +2965,23 @@ unsigned CastInst::isEliminableCastPair(Instruction::CastOps firstOp,
       // zext, sext -> zext, because sext can't sign extend after zext
       return Instruction::ZExt;
     case 11: {
-      // inttoptr, ptrtoint/ptrtoaddr -> bitcast if SrcSize<=PtrSize/AddrSize
-      // and SrcSize==DstSize
+      // inttoptr, ptrtoint/ptrtoaddr -> integer cast
       if (!DL)
         return 0;
       unsigned MidSize = secondOp == Instruction::PtrToAddr
                              ? DL->getAddressSizeInBits(MidTy)
                              : DL->getPointerTypeSizeInBits(MidTy);
       unsigned SrcSize = SrcTy->getScalarSizeInBits();
       unsigned DstSize = DstTy->getScalarSizeInBits();
-      // TODO: Could also produce zext or trunc here.
-      if (SrcSize <= MidSize && SrcSize == DstSize)
-        return Instruction::BitCast;
-      return 0;
+      // If the middle size is smaller than both source and destination,
+      // an additional masking operation would be required.
+      if (MidSize < SrcSize && MidSize < DstSize)
+        return 0;
+      if (DstSize < SrcSize)
+        return Instruction::Trunc;
+      if (DstSize > SrcSize)
+        return Instruction::ZExt;
+      return Instruction::BitCast;
     }
     case 12:
       // addrspacecast, addrspacecast -> bitcast,       if SrcAS == DstAS

llvm/test/Transforms/InstCombine/ptrtoaddr.ll

@@ -23,10 +23,7 @@ define i64 @ptrtoaddr_inttoptr_arg(i64 %a) {
 define i32 @ptrtoaddr_inttoptr_arg_addrsize(i32 %a) {
 ; CHECK-LABEL: define i32 @ptrtoaddr_inttoptr_arg_addrsize(
 ; CHECK-SAME: i32 [[A:%.*]]) {
-; CHECK-NEXT:    [[TMP1:%.*]] = zext i32 [[A]] to i64
-; CHECK-NEXT:    [[TOPTR:%.*]] = inttoptr i64 [[TMP1]] to ptr addrspace(1)
-; CHECK-NEXT:    [[TOADDR:%.*]] = ptrtoaddr ptr addrspace(1) [[TOPTR]] to i32
-; CHECK-NEXT:    ret i32 [[TOADDR]]
+; CHECK-NEXT:    ret i32 [[A]]
 ;
   %toptr = inttoptr i32 %a to ptr addrspace(1)
   %toaddr = ptrtoaddr ptr addrspace(1) %toptr to i32

llvm/unittests/IR/InstructionsTest.cpp

@@ -637,6 +637,30 @@ TEST(InstructionsTest, isEliminableCastPair) {
                                            Int64Ty, &DL1),
             0U);
 
+  // Destination larger than source. Pointer type same as destination.
+  EXPECT_EQ(CastInst::isEliminableCastPair(CastInst::IntToPtr,
+                                           CastInst::PtrToInt, Int16Ty, PtrTy64,
+                                           Int64Ty, &DL1),
+            CastInst::ZExt);
+
+  // Destination larger than source. Pointer type different from destination.
+  EXPECT_EQ(CastInst::isEliminableCastPair(CastInst::IntToPtr,
+                                           CastInst::PtrToInt, Int16Ty, PtrTy32,
+                                           Int64Ty, &DL1),
+            CastInst::ZExt);
+
+  // Destination smaller than source. Pointer type same as source.
+  EXPECT_EQ(CastInst::isEliminableCastPair(CastInst::IntToPtr,
+                                           CastInst::PtrToInt, Int64Ty, PtrTy64,
+                                           Int16Ty, &DL1),
+            CastInst::Trunc);
+
+  // Destination smaller than source. Pointer type different from source.
+  EXPECT_EQ(CastInst::isEliminableCastPair(CastInst::IntToPtr,
+                                           CastInst::PtrToInt, Int64Ty, PtrTy32,
+                                           Int16Ty, &DL1),
+            CastInst::Trunc);
+
   // Test that we don't eliminate bitcasts between different address spaces,
   // or if we don't have available pointer size information.
   DataLayout DL2("e-p:32:32:32-p1:16:16:16-p2:64:64:64-i1:8:8-i8:8:8-i16:16:16"