#14619: Output value of program changes upon compiling with -O optimizations -------------------------------------+------------------------------------- Reporter: sheaf | Owner: (none) Type: bug | Status: new Priority: highest | Milestone: 8.4.1 Component: Compiler | Version: 8.2.2 Resolution: | Keywords: Operating System: Windows | Architecture: x86_64 Type of failure: Incorrect result | (amd64) at runtime | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by AndreasK): I think the sinking pass is fine, the code below fails: {{{ c3Yz: // global _s3Wg::F64 = %MO_F_Add_W64(%MO_F_Add_W64(%MO_F_Mul_W64(D1, D4), %MO_F_Mul_W64(D2, D5)), %MO_F_Mul_W64(D3, D6)); if (%MO_F_Lt_W64(_s3Wg::F64, 0.0 :: W64)) goto c3Zq; else goto c3Zp; c3Zp: // global _s3We::F64 = D5; _s3Wd::F64 = D4; _s3Wc::F64 = D3; _s3Wb::F64 = D2; _s3Wa::F64 = D1; (_c3YT::F64) = call MO_F64_Sqrt(_s3Wg::F64); _s3Wn::F64 = %MO_F_Sub_W64(_s3Wg::F64, _c3YT::F64); if (%MO_F_Gt_W64(_s3Wn::F64, 0.0 :: W64)) goto c3Zn; else goto c3Zi; c3Zn: // global I64[Hp - 40] = GHC.Types.D#_con_info; F64[Hp - 32] = D6; I64[Hp - 24] = GHC.Types.D#_con_info; F64[Hp - 16] = _s3We::F64; I64[Hp - 8] = GHC.Types.D#_con_info; F64[Hp] = _s3Wd::F64; R3 = Hp - 39; R2 = Hp - 23; R1 = Hp - 7; call (P64[Sp])(R3, R2, R1) args: 8, res: 0, upd: 8; ... }}} If we respect the calling convention and MO_F_Add/Mul don't clobber their arguments the code would be fine. I guess the liveness analysis when assigning registers thinks sqrt clobbers D6/xmm6 anyway so it's free to use it as a scratch register before that. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14619#comment:33 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler