Assertion failed: (LHSCst != RHSCst && "Compares not folded above?")

I'm trying to compile ICU v4.8.1 with Alchemy, but am running into an LLVM problem:

Assertion failed: (LHSCst != RHSCst && "Compares not folded above?"), function visitAnd, file /Volumes/data/dev/FlaCC/llvm-2.1/lib/Transforms/Scalar/InstructionCombining.cpp, line 3465.
0   llvm-ld                             0x00264aee _ZNSt8_Rb_treeIN4llvm3sys4PathES2_St9_IdentityIS2_ESt4lessIS2_ESaIS2_EE13insert_uniqueERKS2_ + 6078
1   llvm-ld                             0x00265092 _ZNSt8_Rb_treeIN4llvm3sys4PathES2_St9_IdentityIS2_ESt4lessIS2_ESaIS2_EE13insert_uniqueERKS2_ + 7522
2   libSystem.B.dylib                   0x970a805b _sigtramp + 43
3   ???                                 0xffffffff 0x0 + 4294967295
4   libSystem.B.dylib                   0x971355a5 raise + 26
5   libSystem.B.dylib                   0x9714b6e4 abort + 93
6   libSystem.B.dylib                   0x9713820f __assert_rtn + 252
7   llvm-ld                             0x000a0816 _ZN4llvm15callDefaultCtorIN91_GLOBAL__N__Volumes_data_dev_FlaCC_llvm_2.1_lib_Transforms_Scalar_GVN.cpp_00000000_4964B02A3GVNEEEPNS_4PassEv + 252214
8   llvm-ld                             0x000cf25e _ZN4llvm11InstVisitorIN108_GLOBAL__N__Volumes_data_dev_FlaCC_llvm_2.1_lib_Transforms_Scalar_InstructionCombining.cpp_00000000_6BB61AFF12InstCombinerEPNS_11InstructionEE5visitERS3_ + 766
9   llvm-ld                             0x000c5895 _ZN4llvm15callDefaultCtorIN91_GLOBAL__N__Volumes_data_dev_FlaCC_llvm_2.1_lib_Transforms_Scalar_GVN.cpp_00000000_4964B02A3GVNEEEPNS_4PassEv + 403893
10  llvm-ld                             0x000c631c _ZN4llvm15callDefaultCtorIN91_GLOBAL__N__Volumes_data_dev_FlaCC_llvm_2.1_lib_Transforms_Scalar_GVN.cpp_00000000_4964B02A3GVNEEEPNS_4PassEv + 406588
11  llvm-ld                             0x002004a6 _ZN4llvm12FunctionPassD1Ev + 20998
12  llvm-ld                             0x002008fa _ZN4llvm12FunctionPassD1Ev + 22106
13  llvm-ld                             0x00200e51 _ZN4llvm12FunctionPassD1Ev + 23473
14  llvm-ld                             0x0020125a _ZN4llvm12FunctionPassD1Ev + 24506
15  llvm-ld                             0x002012da _ZN4llvm12FunctionPassD1Ev + 24634
16  llvm-ld                             0x00002f10 0x0 + 12048
17  llvm-ld                             0x000091e2 _ZN4llvm2cl3optINS_12PluginLoaderELb0ENS0_6parserISsEEE16handleOccurrenceEjPKcRKSs + 11986
18  llvm-ld                             0x00002706 0x0 + 9990
make[2]: *** [../../bin/genrb] Error 6
make[1]: *** [all-recursive] Error 2
make: *** [all-recursive] Error 2

What kind of code leads to this problem in the linker? It seems to have something to do with casting ("left-hand-side-cast != right-hand-side-cast"). I'm not above modifying the ICU code to make it compile, but I'm not sure what to modify.

Could be any number of things. The likely cause is bad llvm IR being fed into the linker. Your best bet is to talk to the Alchemy guys and see what they're doing and get them to debug it.