8337683: Fix -Wconversion problem with arrayOop.hpp #20431

coleenp · 2024-08-01T18:49:34Z

Since base_offset_in_bytes and HeapWordSize are int, there's no loss of conversion in making these variables int. This seems trivial.
Tested with tier1 on linux and windows.

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JDK-8337683: Fix -Wconversion problem with arrayOop.hpp (Enhancement - P4)

Reviewers

Stefan Karlsson (@stefank - Reviewer)
David Holmes (@dholmes-ora - Reviewer)

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bridgekeeper · 2024-08-01T18:50:26Z

👋 Welcome back coleenp! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

openjdk · 2024-08-01T18:51:27Z

@coleenp This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8337683: Fix -Wconversion problem with arrayOop.hpp

Reviewed-by: stefank, dholmes

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 63 new commits pushed to the master branch:

4b740d8: 8225209: jdk/jfr/event/compiler/TestCodeSweeper.java fails
ddbd7a7: 8337320: Update ProblemList.txt with tests known to fail on XWayland
12c553f: 8329471: Remove GTK2
088871c: 8335267: [XWayland] move screencast tokens from .awt to .java folder
3bc4a1a: 8233068: HIDPI: Linux: AWT Checkbox check mark is unscaled
a9460a6: 8337982: Remove dead undef assrt0n
fa18359: 8335981: ProblemList runtime/Thread/TestAlwaysPreTouchStacks.java for MacOS
1846a65: 8337205: Typo in Stack vs Deque Method table in Deque specification
16df9c3: 8337971: Problem list several jvmci tests on linux-riscv64 until JDK-8331704 is fixed
9b11bd7: 8337826: Improve logging in OCSPTimeout and SimpleOCSPResponder to help diagnose JDK-8309754
... and 53 more: https://git.openjdk.org/jdk/compare/f1fa64b6b67f2eef916b8d92eb522ccb19035e12...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

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openjdk · 2024-08-01T18:52:00Z

@coleenp The following label will be automatically applied to this pull request:

hotspot

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

mlbridge · 2024-08-01T18:55:05Z

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stefank

This doesn't seem to be enough to fix -Wconversion for this file. It just pushes the problem down to line 142.

I ran your patch with -Wconversion -ferror-limit=20000 and searched for arrayOop.hpp and it gives me:

src/hotspot/share/oops/arrayOop.hpp:71:17: error: implicit conversion changes signedness: 'int' to 'unsigned long' [-Werror,-Wsign-conversion]
    size_t hs = length_offset_in_bytes() + sizeof(int);
                ^~~~~~~~~~~~~~~~~~~~~~~~ ~
src/hotspot/share/oops/arrayOop.hpp:91:17: error: implicit conversion changes signedness: 'int' to 'size_t' (aka 'unsigned long') [-Werror,-Wsign-conversion]
    size_t hs = header_size_in_bytes();
           ~~   ^~~~~~~~~~~~~~~~~~~~~~
src/hotspot/share/oops/arrayOop.hpp:142:43: error: implicit conversion changes signedness: 'int' to 'unsigned long' [-Werror,-Wsign-conversion]
      align_down((SIZE_MAX/HeapWordSize - hdr_size_in_words), MinObjAlignment);
                                        ~ ^~~~~~~~~~~~~~~~~
src/hotspot/share/oops/arrayOop.hpp:144:53: error: implicit conversion changes signedness: 'int' to 'unsigned long' [-Werror,-Wsign-conversion]
      HeapWordSize * max_element_words_per_size_t / type2aelembytes(type);
                                                  ~ ^~~~~~~~~~~~~~~~~~~~~

coleenp · 2024-08-02T11:59:49Z

I run with this:

diff --git a/make/autoconf/flags-cflags.m4 b/make/autoconf/flags-cflags.m4
index cf7f4534c89..131e9ece31c 100644
--- a/make/autoconf/flags-cflags.m4
+++ b/make/autoconf/flags-cflags.m4
@@ -186,12 +186,12 @@ AC_DEFUN([FLAGS_SETUP_WARNINGS],
     gcc)
       DISABLE_WARNING_PREFIX="-Wno-"
       BUILD_CC_DISABLE_WARNING_PREFIX="-Wno-"
-      CFLAGS_WARNINGS_ARE_ERRORS="-Werror"
+      CFLAGS_WARNINGS_ARE_ERRORS=""
 
       # Additional warnings that are not activated by -Wall and -Wextra
       WARNINGS_ENABLE_ADDITIONAL="-Wpointer-arith -Wsign-compare \
           -Wunused-function -Wundef -Wunused-value -Wreturn-type \
-          -Wtrampolines"
+          -Wtrampolines -Wconversion"
       WARNINGS_ENABLE_ADDITIONAL_CXX="-Woverloaded-virtual -Wreorder"
       WARNINGS_ENABLE_ALL_CFLAGS="-Wall -Wextra -Wformat=2 $WARNINGS_ENABLE_ADDITIONAL"
       WARNINGS_ENABLE_ALL_CXXFLAGS="$WARNINGS_ENABLE_ALL_CFLAGS 
$WARNINGS_ENABLE_ADDITIONAL_CXX"

It doesn't check sign change, which all of the files have a million of these errors. Only size change. At some point, I thought that fixing all the multitudes of -Wsign-conversion errors is an impossible task.

coleenp · 2024-08-05T13:35:19Z

If I add in the -Wsign-conversion flags, there's a lot more lines that give an error (everywhere). I can close this as WNF if just fixing the -Wconversion error isn't helpful. @stefank

coleenp · 2024-08-07T23:19:48Z

These GHA compilers are happy with this change now, please re-review.

dholmes-ora · 2024-08-08T05:08:52Z

src/hotspot/share/utilities/byteswap.hpp

-    return (((x & UINT16_C(0x00ff)) << 8) | ((x & UINT16_C(0xff00)) >> 8));
+    return checked_cast<uint16_t>(((x & UINT16_C(0x00ff)) << 8) | ((x & UINT16_C(0xff00)) >> 8));


What is the type of the expression without the cast?

The type of the expression is int.

https://en.cppreference.com/w/cpp/language/implicit_conversion

In particular, arithmetic operators do not accept types smaller than int as arguments, and integral promotions are automatically applied after lvalue-to-rvalue conversion, if applicable.

dholmes-ora · 2024-08-08T05:11:41Z

src/hotspot/share/oops/arrayOop.hpp

-    size_t hs = length_offset_in_bytes() + sizeof(int);
+    int hs = length_offset_in_bytes() + (int)sizeof(int);
 #ifdef ASSERT
    // make sure it isn't called before UseCompressedOops is initialized.
-    static size_t arrayoopdesc_hs = 0;
+    static int arrayoopdesc_hs = 0;


Why not just do a checked_cast<int> on the return statement? (or even a range assert and a static cast?)

Because restricting the types is better than checked_cast. The return type of length_offset_in_bytes() is int.

Also I think the current checked_cast still has problems with signed <--> unsigned.

Another technique to use an even more restricted type. For example, if these offset_in_bytes() functions returned uint16_t, then the value can be widened to either int or size_t without a cast.

Yes that would be a change that we could make that would help, and these offset_in_bytes functions should return an unsigned type since they're never negative.

stefank · 2024-08-08T07:36:37Z

src/hotspot/share/utilities/byteswap.hpp

-    return (((x & UINT16_C(0x00ff)) << 8) | ((x & UINT16_C(0xff00)) >> 8));
+    return checked_cast<uint16_t>(((x & UINT16_C(0x00ff)) << 8) | ((x & UINT16_C(0xff00)) >> 8));


The type of the expression is int.

https://en.cppreference.com/w/cpp/language/implicit_conversion

In particular, arithmetic operators do not accept types smaller than int as arguments, and integral promotions are automatically applied after lvalue-to-rvalue conversion, if applicable.

stefank · 2024-08-08T07:38:33Z

src/hotspot/share/runtime/atomic.hpp

@@ -1118,7 +1119,7 @@ inline T Atomic::CmpxchgByteUsingInt::operator()(T volatile* dest,
  uint8_t canon_compare_value = compare_value;
  volatile uint32_t* aligned_dest
    = reinterpret_cast<volatile uint32_t*>(align_down(dest, sizeof(uint32_t)));
-  size_t offset = pointer_delta(dest, aligned_dest, 1);
+  uint32_t offset = checked_cast<uint32_t>(pointer_delta(dest, aligned_dest, 1));


If this works for all compilers, then that's great. I was a bit concerned that the code in the statement below would cause a warning:

(sizeof(uint32_t) - 1 - offset)

given that sizeof returns a size_t and 1 an int, but I guess the compilers are smart enough to figure out that they all fit within a uint32_t?

gcc doesn't complain about this with -Wsign-conversion, or at least as included with arrayOop.hpp, which was the only goal of this change was to fix the new -Wconversion warning with arrayOop.hpp.

coleenp

Thanks for reviewing Stefan and suggestions for byteswap.hpp and atomic.hpp.

coleenp · 2024-08-08T11:14:48Z

src/hotspot/share/runtime/atomic.hpp

@@ -1118,7 +1119,7 @@ inline T Atomic::CmpxchgByteUsingInt::operator()(T volatile* dest,
  uint8_t canon_compare_value = compare_value;
  volatile uint32_t* aligned_dest
    = reinterpret_cast<volatile uint32_t*>(align_down(dest, sizeof(uint32_t)));
-  size_t offset = pointer_delta(dest, aligned_dest, 1);
+  uint32_t offset = checked_cast<uint32_t>(pointer_delta(dest, aligned_dest, 1));


gcc doesn't complain about this with -Wsign-conversion, or at least as included with arrayOop.hpp, which was the only goal of this change was to fix the new -Wconversion warning with arrayOop.hpp.

dholmes-ora

Ok.

coleenp · 2024-08-08T16:09:54Z

Thanks for reviewing Stefan and David.
/integrate

openjdk · 2024-08-08T16:11:09Z

Going to push as commit 9695f09.
Since your change was applied there have been 65 commits pushed to the master branch:

78773b1: 8338015: Fix "Java Java" typo in package info file of java.lang.classfile
6a9a867: 8337994: [REDO] Native memory leak when not recording any events
4b740d8: 8225209: jdk/jfr/event/compiler/TestCodeSweeper.java fails
ddbd7a7: 8337320: Update ProblemList.txt with tests known to fail on XWayland
12c553f: 8329471: Remove GTK2
088871c: 8335267: [XWayland] move screencast tokens from .awt to .java folder
3bc4a1a: 8233068: HIDPI: Linux: AWT Checkbox check mark is unscaled
a9460a6: 8337982: Remove dead undef assrt0n
fa18359: 8335981: ProblemList runtime/Thread/TestAlwaysPreTouchStacks.java for MacOS
1846a65: 8337205: Typo in Stack vs Deque Method table in Deque specification
... and 55 more: https://git.openjdk.org/jdk/compare/f1fa64b6b67f2eef916b8d92eb522ccb19035e12...master

Your commit was automatically rebased without conflicts.

openjdk · 2024-08-08T16:11:15Z

@coleenp Pushed as commit 9695f09.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

8337683: Fix -Wconversion problem with arrayOop.hpp

01b3cf4

openjdk bot added the rfr Pull request is ready for review label Aug 1, 2024

openjdk bot added the hotspot hotspot-dev@openjdk.org label Aug 1, 2024

stefank suggested changes Aug 2, 2024

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coleenp added 4 commits August 7, 2024 16:35

Fix additional -Wsign-conversion errors, contributed by Stefan.

4ac5282

Fix compilation error and use pointer_delta_as_int instead.

acbdbbd

Add include file.

f14a675

See if GHA compilers like this.

22c1697

dholmes-ora reviewed Aug 8, 2024

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stefank approved these changes Aug 8, 2024

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coleenp commented Aug 8, 2024

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coleenp deleted the arrayoop branch August 8, 2024 16:11

		return (((x & UINT16_C(0x00ff)) << 8) \| ((x & UINT16_C(0xff00)) >> 8));
		return checked_cast<uint16_t>(((x & UINT16_C(0x00ff)) << 8) \| ((x & UINT16_C(0xff00)) >> 8));

8337683: Fix -Wconversion problem with arrayOop.hpp #20431

8337683: Fix -Wconversion problem with arrayOop.hpp #20431

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