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| author | Richard Biener <rguenther@suse.de> | 2021-05-03 12:07:58 +0200 |
|---|---|---|
| committer | Richard Biener <rguenther@suse.de> | 2021-05-03 15:11:03 +0200 |
| commit | 32955416d8040b1fa1ba21cd4179b3264e6c5bd6 (patch) | |
| tree | 12f8a6b4cf1079178105266a7b4ff4a36296899d /gcc/tree-ssa-dse.c | |
| parent | ed3c43224cc4e378dbab066122bc63536ccb1276 (diff) | |
| download | gcc-32955416d8040b1fa1ba21cd4179b3264e6c5bd6.zip gcc-32955416d8040b1fa1ba21cd4179b3264e6c5bd6.tar.gz gcc-32955416d8040b1fa1ba21cd4179b3264e6c5bd6.tar.bz2 | |
Improve PHI handling in DSE
This improves handling of PHI defs when walking uses in
dse_classify_store to track two PHI defs. This happens
when there are CFG merges and one PHI feeds into another.
If we decide to want more then using a sbitmap for this might be
the way to go.
2021-05-03 Richard Biener <rguenther@suse.de>
* tree-ssa-dse.c (dse_classify_store): Track two PHI defs.
* gcc.dg/tree-ssa/ssa-dse-42.c: New testcase.
* gcc.dg/pr81192.c: Disable DSE.
Diffstat (limited to 'gcc/tree-ssa-dse.c')
| -rw-r--r-- | gcc/tree-ssa-dse.c | 23 |
1 files changed, 14 insertions, 9 deletions
diff --git a/gcc/tree-ssa-dse.c b/gcc/tree-ssa-dse.c index e0a944c..dfa6d31 100644 --- a/gcc/tree-ssa-dse.c +++ b/gcc/tree-ssa-dse.c @@ -799,7 +799,8 @@ dse_classify_store (ao_ref *ref, gimple *stmt, return DSE_STORE_LIVE; auto_vec<gimple *, 10> defs; - gimple *phi_def = NULL; + gimple *first_phi_def = NULL; + gimple *last_phi_def = NULL; FOR_EACH_IMM_USE_STMT (use_stmt, ui, defvar) { /* Limit stmt walking. */ @@ -825,7 +826,9 @@ dse_classify_store (ao_ref *ref, gimple *stmt, SSA_NAME_VERSION (PHI_RESULT (use_stmt)))) { defs.safe_push (use_stmt); - phi_def = use_stmt; + if (!first_phi_def) + first_phi_def = use_stmt; + last_phi_def = use_stmt; } } /* If the statement is a use the store is not dead. */ @@ -889,6 +892,8 @@ dse_classify_store (ao_ref *ref, gimple *stmt, gimple *def = defs[i]; gimple *use_stmt; use_operand_p use_p; + tree vdef = (gimple_code (def) == GIMPLE_PHI + ? gimple_phi_result (def) : gimple_vdef (def)); /* If the path to check starts with a kill we do not need to process it further. ??? With byte tracking we need only kill the bytes currently @@ -901,8 +906,7 @@ dse_classify_store (ao_ref *ref, gimple *stmt, } /* If the path ends here we do not need to process it further. This for example happens with calls to noreturn functions. */ - else if (gimple_code (def) != GIMPLE_PHI - && has_zero_uses (gimple_vdef (def))) + else if (has_zero_uses (vdef)) { /* But if the store is to global memory it is definitely not dead. */ @@ -912,12 +916,13 @@ dse_classify_store (ao_ref *ref, gimple *stmt, } /* In addition to kills we can remove defs whose only use is another def in defs. That can only ever be PHIs of which - we track a single for simplicity reasons (we fail for multiple - PHIs anyways). We can also ignore defs that feed only into + we track two for simplicity reasons, the first and last in + {first,last}_phi_def (we fail for multiple PHIs anyways). + We can also ignore defs that feed only into already visited PHIs. */ - else if (gimple_code (def) != GIMPLE_PHI - && single_imm_use (gimple_vdef (def), &use_p, &use_stmt) - && (use_stmt == phi_def + else if (single_imm_use (vdef, &use_p, &use_stmt) + && (use_stmt == first_phi_def + || use_stmt == last_phi_def || (gimple_code (use_stmt) == GIMPLE_PHI && bitmap_bit_p (visited, SSA_NAME_VERSION |