[llvm] [IR] Handle trunc for ptrtoaddr(inttoptr) cast pair (PR #162842)

[Alexander Richardson via llvm-commits]

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@@ -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,
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arichardson wrote:

Could you also add a ptrtoaddr test here with e.g. `p2:64:64:64:32` data layout? Showing it only works for the address bits?

https://github.com/llvm/llvm-project/pull/162842