From 6cedf5d8e23c862db147e71d5767ca57e6b4f433 Mon Sep 17 00:00:00 2001 From: Richard Sandiford Date: Mon, 27 Jan 2020 19:37:55 +0000 Subject: [PATCH] predcom: Fix invalid store-store commoning [PR93434] predcom has the following code to stop one rogue load from interfering with other store-load opportunities: /* If A is read and B write or vice versa and there is unsuitable dependence, instead of merging both components into a component that will certainly not pass suitable_component_p, just put the read into bad component, perhaps at least the write together with all the other data refs in it's component will be optimizable. */ But when store-store commoning was added later, this had the effect of ignoring loads that occur between two candidate stores. There is code further up to handle loads and stores with unknown dependences: /* Don't do store elimination if there is any unknown dependence for any store data reference. */ if ((DR_IS_WRITE (dra) || DR_IS_WRITE (drb)) && (DDR_ARE_DEPENDENT (ddr) == chrec_dont_know || DDR_NUM_DIST_VECTS (ddr) == 0)) eliminate_store_p = false; But the store-load code above skips loads for *known* dependences if (a) the load has already been marked "bad" or (b) the data-ref machinery knows the dependence distance, but determine_offsets can't handle the combination. (a) happens to be the problem in the testcase, but a different sequence could have given (b) instead. We have writes to individual fields of a structure and reads from the whole structure. Since determine_offsets requires the types to be the same, it returns false for each such read/write combination. This patch records which components have had loads removed and prevents store-store commoning for them. It's a bit too pessimistic, since there shouldn't be a problem if a "bad" load dominates all stores in a component. But (a) we can't AFAIK use pcom_stmt_dominates_stmt_p here and (b) the handling for that case would probably need to be removed again if we handled more exotic cases in future. 2020-01-28 Richard Sandiford gcc/ PR tree-optimization/93434 * tree-predcom.c (split_data_refs_to_components): Record which components have had aliasing loads removed. Prevent store-store commoning for all such components. gcc/testsuite/ PR tree-optimization/93434 * gcc.c-torture/execute/pr93434.c: New test. --- gcc/ChangeLog | 7 ++++ gcc/testsuite/ChangeLog | 5 +++ gcc/testsuite/gcc.c-torture/execute/pr93434.c | 36 +++++++++++++++++++ gcc/tree-predcom.c | 24 +++++++++++-- 4 files changed, 70 insertions(+), 2 deletions(-) create mode 100644 gcc/testsuite/gcc.c-torture/execute/pr93434.c diff --git a/gcc/ChangeLog b/gcc/ChangeLog index 3489428938c..8507c2e439d 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,10 @@ +2020-01-28 Richard Sandiford + + PR tree-optimization/93434 + * tree-predcom.c (split_data_refs_to_components): Record which + components have had aliasing loads removed. Prevent store-store + commoning for all such components. + 2020-01-28 Jakub Jelinek PR target/93418 diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog index e3f7592b5f6..eac18206b12 100644 --- a/gcc/testsuite/ChangeLog +++ b/gcc/testsuite/ChangeLog @@ -1,3 +1,8 @@ +2020-01-28 Richard Sandiford + + PR tree-optimization/93434 + * gcc.c-torture/execute/pr93434.c: New test. + 2020-01-28 Richard Sandiford PR testsuite/93460 diff --git a/gcc/testsuite/gcc.c-torture/execute/pr93434.c b/gcc/testsuite/gcc.c-torture/execute/pr93434.c new file mode 100644 index 00000000000..e786252794b --- /dev/null +++ b/gcc/testsuite/gcc.c-torture/execute/pr93434.c @@ -0,0 +1,36 @@ +typedef struct creal_T { + double re; + double im; +} creal_T; + +#define N 16 +int main() { + int k; + int i; + int j; + creal_T t2[N]; + double inval; + + inval = 1.0; + for (j = 0; j < N; ++j) { + t2[j].re = 0; + t2[j].im = 0; + } + + for (j = 0; j < N/4; j++) { + i = j * 4; + t2[i].re = inval; + t2[i].im = inval; + k = i + 3; + t2[k].re = inval; + t2[k].im = inval; + t2[i] = t2[k]; + t2[k].re = inval; + } + + for (i = 0; i < 2; ++i) + if (t2[i].re != !i || t2[i].im != !i) + __builtin_abort (); + + return 0; +} diff --git a/gcc/tree-predcom.c b/gcc/tree-predcom.c index 047c7fa9583..d2dcfe7f42d 100644 --- a/gcc/tree-predcom.c +++ b/gcc/tree-predcom.c @@ -767,6 +767,7 @@ split_data_refs_to_components (class loop *loop, /* Don't do store elimination if loop has multiple exit edges. */ bool eliminate_store_p = single_exit (loop) != NULL; basic_block last_always_executed = last_always_executed_block (loop); + auto_bitmap no_store_store_comps; FOR_EACH_VEC_ELT (datarefs, i, dr) { @@ -838,9 +839,13 @@ split_data_refs_to_components (class loop *loop, else if (DR_IS_READ (dra) && ib != bad) { if (ia == bad) - continue; + { + bitmap_set_bit (no_store_store_comps, ib); + continue; + } else if (!determine_offset (dra, drb, &dummy_off)) { + bitmap_set_bit (no_store_store_comps, ib); merge_comps (comp_father, comp_size, bad, ia); continue; } @@ -848,9 +853,13 @@ split_data_refs_to_components (class loop *loop, else if (DR_IS_READ (drb) && ia != bad) { if (ib == bad) - continue; + { + bitmap_set_bit (no_store_store_comps, ia); + continue; + } else if (!determine_offset (dra, drb, &dummy_off)) { + bitmap_set_bit (no_store_store_comps, ia); merge_comps (comp_father, comp_size, bad, ib); continue; } @@ -908,6 +917,17 @@ split_data_refs_to_components (class loop *loop, comp->refs.quick_push (dataref); } + if (eliminate_store_p) + { + bitmap_iterator bi; + EXECUTE_IF_SET_IN_BITMAP (no_store_store_comps, 0, ia, bi) + { + ca = component_of (comp_father, ia); + if (ca != bad) + comps[ca]->eliminate_store_p = false; + } + } + for (i = 0; i < n; i++) { comp = comps[i]; -- 2.30.2