Hi Richard, Thanks for the review!
on 2020/11/10 下午7:31, Richard Sandiford wrote: > "Kewen.Lin" <li...@linux.ibm.com> writes: >> Hi, >> >> As Lyon pointed out, the newly introduced test case >> gcc.dg/tree-ssa/pr96789.c fails on arm-none-linux-gnueabihf. >> Loop vectorizer is able to vectorize the two loops which >> operate on array tmp with load_lanes feature support. It >> makes dse3 get unexpected inputs and do nothing. >> >> This patch is to teach the case to respect vect_load_lanes, >> meanwhile to guard the check only under vect_int. > > I'm not sure this is the right check. The test passes on aarch64, > which also has load lanes, but apparently doesn't use them for this > test. I think the way the loop vectoriser handles the loops will > depend a lot on target costs, which can vary in unpredictable ways. > You are right, although aarch64 doesn't have this failure, it can fail with explicit -march=armv8-a+sve. It can vary as target features/costs change. The check is still fragile. Your suggestion with -ftree-slp-vectorize below is better! > Does it work if you instead change -ftree-vectorize to -ftree-slp-vectorize? > Or does that defeat the purpose of the test? It works, nice, thanks for the suggestion! I appended one explicit -fno-tree-loop-vectorize to avoid it to fail in case someone kicks off the testing with explicit -ftree-loop-vectorize. The updated version is pasted below, is it ok for trunk? BR, Kewen ----- gcc/testsuite/ChangeLog: * gcc.dg/tree-ssa/pr96789.c: Adjusted by disabling loop vectorization. diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr96789.c b/gcc/testsuite/gcc.dg/tree-ssa/pr96789.c index d6139a014d8..5704952309b 100644 --- a/gcc/testsuite/gcc.dg/tree-ssa/pr96789.c +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr96789.c @@ -1,5 +1,8 @@ /* { dg-do compile } */ -/* { dg-options "-O2 -funroll-loops -ftree-vectorize -fdump-tree-dse-details" } */ +/* Disable loop vectorization to avoid that loop vectorizer + optimizes those two loops that operate tmp array so that + subsequent dse3 won't eliminate expected tmp stores. */ +/* { dg-options "-O2 -funroll-loops -ftree-slp-vectorize -fno-tree-loop-vectorize -fdump-tree-dse-details" } */ /* Test if scalar cleanup pass takes effects, mainly check its secondary pass DSE can remove dead stores on array