#11792: Optimised unsafe FFI call can get wrong argument -------------------------------------+------------------------------------- Reporter: Szunti | Owner: Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 7.10.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect result | Unknown/Multiple at runtime | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by hsyl20): Replying to [comment:5 osa1]:
{{{ third arg: [ movl $7457,%edx] fourth arg: [ movl $255,%vI_n4I8, movq 7(%rbx),%vI_n4Ia, imulq %vI_s4pW,%vI_n4Ia, movl %vI_n4Ia,%eax, xorq %rdx,%rdx, }}}
These look correct to me. Since the code mostly uses virtual registers `%edx` isn't overridden at this point.
It is overriden: `%rdx` is `xor`ed before each `divq`. With -ddump-asm- liveness, we can see that `%edx` (`%r3`) born in the `movl` is overwritten. {{{ movl $7457,%edx # born: %r3 # w_dying: %r3 movl $255,%vI_n413 # born: %vI_n413 movq 7(%rbx),%vI_n415 # born: %vI_n415 # r_dying: %r1 imulq %vI_s3Mw,%vI_n415 movl %vI_n415,%eax # born: %r0 # r_dying: %vI_n415 xorq %rdx,%rdx # born: %r3 divq %vI_n413 # r_dying: %vI_n413 # w_dying: %r3 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11792#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler