this loop does not vectorize #include<cmath> float a,b,c,d; float z[1024]; bool ok[1024]; constexpr float rBig = 150.; void foo() { for (int i=0;i!=1024;++i) { float rR = a*z[i]; float rL = b*z[i]; float rMin = (rR<rL) ? rR : rL; float rMax = (rR<rL) ? rL : rR; //rMin = (rMax>0) ? rMin : rBig+std::abs(z[i]); // this vectorize (sic...) rMin = (rMax>0) ? rMin : rBig; // comment to vectorize rMin = (rMin>0) ? rMin : rMax; ok[i] = rMin-c<rMax+d; } } c++ -std=c++11 -Ofast -march=corei7 -c range.cc -ftree-vectorizer-verbose=1 Analyzing loop at range.cc:8 range.cc:7: note: vectorized 0 loops in function. range.cc:16: note: vect_recog_bool_pattern: detected: range.cc:16: note: pattern recognized: VIEW_CONVERT_EXPR<unsigned char>(ok[i_22]) = patt_15; range.cc:16: note: additional pattern stmt: patt_13 = _14 < _16 ? 1 : 0; adding to "rBig" std::abs(z[i]) it does c++ -std=c++11 -Ofast -march=corei7 -c range.cc -ftree-vectorizer-verbose=1 Analyzing loop at range.cc:8 range.cc:8: note: vect_recog_bool_pattern: detected: range.cc:8: note: pattern recognized: VIEW_CONVERT_EXPR<unsigned char>(ok[i_24]) = patt_16; range.cc:8: note: additional pattern stmt: patt_14 = _15 < _17 ? 1 : 0; Vectorizing loop at range.cc:8 range.cc:8: note: LOOP VECTORIZED. range.cc:7: note: vectorized 1 loops in function.
if-conversion is confused by the three-argument PHI node: <bb 6>: # rMin_3 = PHI <rMin_11(5), rMin_12(4), 1.5e+2(3)> that occurs because of the forwarder block (which isn't one in the case the addition appears). DOM produces this by threading if (rMin_12 > 0.0) goto <bb 4>; else goto <bb 5>; <bb 4>: <bb 5>: # rMin_2 = PHI <rMin_11(4), 1.5e+2(3)> if (rMin_2 > 0.0) goto <bb 7>; else goto <bb 6>; ... <bb 7>: # rMin_3 = PHI <rMin_2(5), rMin_12(6)> for rMin_2 == 1.5e+2. That's a good optimization.
If-conversion will handle the three-arg phi node, if aggressive_if_conv is true, i.e. if loop->force_vectorize. I believe it's possible to set this using a #pragma (?), but I haven't managed yet. A question might be whether it's safe to deal with three-arg phi-nodes when !aggressive_if_conv...
Author: amker Date: Tue May 3 09:04:46 2016 New Revision: 235808 URL: https://gcc.gnu.org/viewcvs?rev=235808&root=gcc&view=rev Log: PR tree-optimization/56541 * doc/invoke.texi (@item max-tree-if-conversion-phi-args): New item. * params.def (PARAM_MAX_TREE_IF_CONVERSION_PHI_ARGS): new param. * tree-if-conv.c (MAX_PHI_ARG_NUM): new macro. (any_complicated_phi): new static variable. (aggressive_if_conv): delete. (if_convertible_phi_p): support phis with more than two arguments. (if_convertible_bb_p): remvoe check on aggressive_if_conv and critical pred edges. (ifcvt_split_critical_edges): support phis with more than two arguments by checking new parameter. only split critical edges if needed. (tree_if_conversion): handle simd pragma marked loop using new local variable aggressive_if_conv. check any_complicated_phi. gcc/testsuite PR tree-optimization/56541 * gcc.dg/tree-ssa/ifc-pr56541.c: new test. * gcc.dg/vect/pr56541.c: new test. Added: trunk/gcc/testsuite/gcc.dg/tree-ssa/ifc-pr56541.c trunk/gcc/testsuite/gcc.dg/vect/pr56541.c Modified: trunk/gcc/ChangeLog trunk/gcc/doc/invoke.texi trunk/gcc/params.def trunk/gcc/testsuite/ChangeLog trunk/gcc/tree-if-conv.c
Fixed on trunk.