#9929: New alias handling not compatible with LLVM 3.4 -------------------------------------+------------------------------------- Reporter: rwbarton | Owner: Type: bug | Status: new Priority: high | Milestone: 7.10.2 Component: Compiler (LLVM) | Version: 7.10.1-rc1 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) crash | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: -------------------------------------+------------------------------------- Changes (by rwbarton): * status: closed => new * resolution: worksforme => Old description:
As reported by Joachim here: https://www.haskell.org/pipermail/ghc- devs/2014-November/007480.html, and it happens for me too. It seems to affect every program compiled with `-fllvm`; T5681 just happens to be the only such program in the normal test suite.
Faced with the definitions {{{ @Main_zdwwork_info_itable$def = internal constant %Main_zdwwork_entry_struct<{ i64 add (i64 sub (i64 ptrtoint (i8* @S2ZH_srt to i64),i64 ptrtoint ( void (i64*, i64*, i64*, i64, i64, i64, i64, i64, i64, i64)* @Main_zdwwork_info$def to i64)),i64 8), i64 4294967299, i64 0, i64 4294967311}>, section "X98A__STRIP,__me3", align 8 @Main_zdwwork_info_itable = alias i8* bitcast (%Main_zdwwork_entry_struct* @Main_zdwwork_info_itable$def to i8*) }}} LLVM 3.4 produced the assembly {{{ .type Main_zdwwork_info_itable,@object # @Main_zdwwork_info_itable .section .rodata,"a",@progbits ; note .rodata, not X98A__STRIP,__me3! .globl Main_zdwwork_info_itable .align 16 Main_zdwwork_info_itable: .quad (S2ZH_srt$def-Main_zdwwork_info$def)+8 .quad 4294967299 # 0x100000003 .quad 0 # 0x0 .quad 4294967311 # 0x10000000f .size Main_zdwwork_info_itable, 32 }}} At first I thought this was an LLVM bug, but after reading http://llvm.org/docs/LangRef.html#linkage-types I'm not sure; maybe the `internal` linkage type means that `@Main_zdwwork_info_itable$def` is just a constant value without any "identity", so the LLVM optimizer is free to drop it, merge it with another constant, or move it to another section?
One workaround would be to use external linkage for these `foo_info_itable$def` symbols, and then if desired (to reduce symbol table size), strip out any `.global bar$def` statements in the LLVM mangler...?
New description: '''Edit''': we're going to leave GHC 7.10 broken with LLVM 3.4 as described below, but then we should at least update GHC's information about which versions of LLVM it can use. ---- As reported by Joachim here: https://www.haskell.org/pipermail/ghc- devs/2014-November/007480.html, and it happens for me too. It seems to affect every program compiled with `-fllvm`; T5681 just happens to be the only such program in the normal test suite. Faced with the definitions {{{ @Main_zdwwork_info_itable$def = internal constant %Main_zdwwork_entry_struct<{ i64 add (i64 sub (i64 ptrtoint (i8* @S2ZH_srt to i64),i64 ptrtoint ( void (i64*, i64*, i64*, i64, i64, i64, i64, i64, i64, i64)* @Main_zdwwork_info$def to i64)),i64 8), i64 4294967299, i64 0, i64 4294967311}>, section "X98A__STRIP,__me3", align 8 @Main_zdwwork_info_itable = alias i8* bitcast (%Main_zdwwork_entry_struct* @Main_zdwwork_info_itable$def to i8*) }}} LLVM 3.4 produced the assembly {{{ .type Main_zdwwork_info_itable,@object # @Main_zdwwork_info_itable .section .rodata,"a",@progbits ; note .rodata, not X98A__STRIP,__me3! .globl Main_zdwwork_info_itable .align 16 Main_zdwwork_info_itable: .quad (S2ZH_srt$def-Main_zdwwork_info$def)+8 .quad 4294967299 # 0x100000003 .quad 0 # 0x0 .quad 4294967311 # 0x10000000f .size Main_zdwwork_info_itable, 32 }}} At first I thought this was an LLVM bug, but after reading http://llvm.org/docs/LangRef.html#linkage-types I'm not sure; maybe the `internal` linkage type means that `@Main_zdwwork_info_itable$def` is just a constant value without any "identity", so the LLVM optimizer is free to drop it, merge it with another constant, or move it to another section? One workaround would be to use external linkage for these `foo_info_itable$def` symbols, and then if desired (to reduce symbol table size), strip out any `.global bar$def` statements in the LLVM mangler...? -- Comment: We should also add a warning telling people to use LLVM 3.5 since we know that that is the version that we need. (I actually thought the existing warning for a too old LLVM version would trigger, but it doesn't.) I've already seen at least one person confused about this thinking that 7.10 has no support for LLVM at all. I'll repurpose this ticket to track that. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9929#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler