| Message ID | 87605v0zq9.fsf@linaro.org |
|---|---|
| State | New |
| Headers | show |
| Series | Don't try to vectorise COND_EXPR reduction chains (PR 84913) | expand |
On March 17, 2018 11:21:18 AM GMT+01:00, Richard Sandiford <richard.sandiford@linaro.org> wrote: >The testcase ICEd for both SVE and AVX512 because we were trying >to vectorise a chain of COND_EXPRs as a reduction and getting >confused by reduc_index == -1. > >We normally handle reduction chains by vectorising all statements >except the last one normally, but that wouldn't work here for the >reasons explained in the comment. > >Tested on aarch64-linux-gnu and x86_64-linux-gnu. OK to install? OK. Richard. >Richard > > >2018-03-17 Richard Sandiford <richard.sandiford@linaro.org> > >gcc/ > PR tree-optimization/84913 > * tree-vect-loop.c (vectorizable_reduction): Don't try to > vectorize chains of COND_EXPRs. > >gcc/testsuite/ > PR tree-optimization/84913 > * gfortran.dg/vect/pr84913.f90: New test. > >Index: gcc/tree-vect-loop.c >=================================================================== >--- gcc/tree-vect-loop.c 2018-03-01 08:20:43.850526185 +0000 >+++ gcc/tree-vect-loop.c 2018-03-17 10:19:19.289947549 +0000 >@@ -6788,6 +6788,30 @@ vectorizable_reduction (gimple *stmt, gi >/* If we have a condition reduction, see if we can simplify it further. > */ > if (v_reduc_type == COND_REDUCTION) > { >+ /* TODO: We can't yet handle reduction chains, since we need to >treat >+ each COND_EXPR in the chain specially, not just the last one. >+ E.g. for: >+ >+ x_1 = PHI <x_3, ...> >+ x_2 = a_2 ? ... : x_1; >+ x_3 = a_3 ? ... : x_2; >+ >+ we're interested in the last element in x_3 for which a_2 || a_3 >+ is true, whereas the current reduction chain handling would >+ vectorize x_2 as a normal VEC_COND_EXPR and only treat x_3 >+ as a reduction operation. */ >+ if (reduc_index == -1) >+ { >+ if (dump_enabled_p ()) >+ dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location, >+ "conditional reduction chains not supported\n"); >+ return false; >+ } >+ >+ /* vect_is_simple_reduction ensured that operand 2 is the >+ loop-carried operand. */ >+ gcc_assert (reduc_index == 2); >+ > /* Loop peeling modifies initial value of reduction PHI, which > makes the reduction stmt to be transformed different to the > original stmt analyzed. We need to record reduction code for >Index: gcc/testsuite/gfortran.dg/vect/pr84913.f90 >=================================================================== >--- /dev/null 2018-03-17 08:19:33.716019995 +0000 >+++ gcc/testsuite/gfortran.dg/vect/pr84913.f90 2018-03-17 >10:19:19.286947657 +0000 >@@ -0,0 +1,13 @@ >+! { dg-do compile } >+ >+function foo(a, b, c, n) >+ integer :: a(n), b(n), c(n), n, i, foo >+ foo = 0 >+ do i = 1, n >+ if (a(i) .eq. b(i)) then >+ foo = 1 >+ else if (a(i) .eq. c(i)) then >+ foo = 2 >+ end if >+ end do >+end function foo
Index: gcc/tree-vect-loop.c =================================================================== --- gcc/tree-vect-loop.c 2018-03-01 08:20:43.850526185 +0000 +++ gcc/tree-vect-loop.c 2018-03-17 10:19:19.289947549 +0000 @@ -6788,6 +6788,30 @@ vectorizable_reduction (gimple *stmt, gi /* If we have a condition reduction, see if we can simplify it further. */ if (v_reduc_type == COND_REDUCTION) { + /* TODO: We can't yet handle reduction chains, since we need to treat + each COND_EXPR in the chain specially, not just the last one. + E.g. for: + + x_1 = PHI <x_3, ...> + x_2 = a_2 ? ... : x_1; + x_3 = a_3 ? ... : x_2; + + we're interested in the last element in x_3 for which a_2 || a_3 + is true, whereas the current reduction chain handling would + vectorize x_2 as a normal VEC_COND_EXPR and only treat x_3 + as a reduction operation. */ + if (reduc_index == -1) + { + if (dump_enabled_p ()) + dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location, + "conditional reduction chains not supported\n"); + return false; + } + + /* vect_is_simple_reduction ensured that operand 2 is the + loop-carried operand. */ + gcc_assert (reduc_index == 2); + /* Loop peeling modifies initial value of reduction PHI, which makes the reduction stmt to be transformed different to the original stmt analyzed. We need to record reduction code for Index: gcc/testsuite/gfortran.dg/vect/pr84913.f90 =================================================================== --- /dev/null 2018-03-17 08:19:33.716019995 +0000 +++ gcc/testsuite/gfortran.dg/vect/pr84913.f90 2018-03-17 10:19:19.286947657 +0000 @@ -0,0 +1,13 @@ +! { dg-do compile } + +function foo(a, b, c, n) + integer :: a(n), b(n), c(n), n, i, foo + foo = 0 + do i = 1, n + if (a(i) .eq. b(i)) then + foo = 1 + else if (a(i) .eq. c(i)) then + foo = 2 + end if + end do +end function foo