#7574: Register allocator chokes on certain branches with literals -----------------------------+---------------------------------------------- Reporter: thoughtpolice | Owner: Type: bug | Status: new Priority: normal | Component: Compiler Version: 7.6.1 | Keywords: Os: Unknown/Multiple | Architecture: Unknown/Multiple Failure: None/Unknown | Blockedby: Blocking: | Related: 7571, 7573 -----------------------------+---------------------------------------------- While running the test for #7571 (test is in #7573,) under '''WAY=normal''' instead of '''WAY=llvm''', I encountered this bug in the native backend: {{{ =====> T7571(normal) 6 of 6 [0, 0, 0] cd . && '/Users/a/code/haskell/ghc/inplace/bin/ghc-stage2' -fforce-recomp -dcore-lint -dcmm-lint -dno-debug-output -no-user-package-db -rtsopts -fno-ghci-history -c T7571.cmm -no-hs-main >T7571.comp.stderr 2>&1 Compile failed (status 256) errors were: ghc-stage2: panic! (the 'impossible' happened) (GHC version 7.7.20130113 for x86_64-apple-darwin): allocateRegsAndSpill: Cannot read from uninitialized register %vI_c7 }}} The test in question is: {{{ #include "Cmm.h" testLiteralBranch (W_ dst, W_ src) { if (1) { prim %memcpy(dst, src, 1024, 4); } else { prim %memcpy(dst, src, 512, 8); } return (); } }}} If you comment out the branch conditionals, the test passes, so clearly something fishy is going on here. The test also fails if you change the condition to ```if (1 == 1)``` I have absolutely no idea how this did not trip the profiling-based build in StgStdThunks.cmm, like in the LLVM build c.f. #7571 -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7574 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler