[01/13] Revert "simplify CBR-CBR on the same condition"

Commit Message

Luc Van Oostenryck March 21, 2021, 12:34 p.m. UTC

The commit 7cd2ce022575 ("simplify CBR-CBR on the same condition")
added a generalization of the existing CBR-CBR simplification
using the dominance tree.

The problem is that as soon as a change is made to the CFG, the
dominance tree become invalid and should be rebuilt (which is costly
to do for each CFG changes) or updated (which is quite complex).

So, for now, revert this commit.

Reverts: 7cd2ce022575fbd383bb39b54f1e0fa402919da2.
Signed-off-by: Luc Van Oostenryck <[e-mail]>
---
 flow.c | 106 ---------------------------------------------------------
 1 file changed, 106 deletions(-)

Patch

diff --git a/flow.c b/flow.c
index c5319ae35ac4..6d77453a3554 100644
--- a/flow.c
+++ b/flow.c
@@ -19,7 +19,6 @@ 
 #include "simplify.h"
 #include "flow.h"
 #include "target.h"
-#include "flowgraph.h"
 
 unsigned long bb_generation;
 
@@ -69,34 +68,6 @@  static int pseudo_truth_value(pseudo_t pseudo)
 	}
 }
 
-///
-// check if the BB is empty or only contains phi-sources
-static int bb_is_trivial(struct basic_block *bb)
-{
-	struct instruction *insn;
-	int n = 0;
-
-	FOR_EACH_PTR(bb->insns, insn) {
-		if (!insn->bb)
-			continue;
-		switch (insn->opcode) {
-		case OP_TERMINATOR ... OP_TERMINATOR_END:
-			return n ? -1 : 1;
-		case OP_NOP:
-		case OP_INLINED_CALL:
-			continue;
-		case OP_PHISOURCE:
-			n++;
-			continue;
-		default:
-			goto out;
-		}
-	} END_FOR_EACH_PTR(insn);
-
-out:
-	return 0;
-}
-
 /*
  * Does a basic block depend on the pseudos that "src" defines?
  */
@@ -158,81 +129,6 @@  out:
 	return false;
 }
 
-///
-// do jump threading in dominated BBs
-// @dom: the BB which must dominate the modified BBs.
-// @old: the old target BB
-// @new: the new target BB
-// @return: 0 if no chnages have been made, 1 otherwise.
-//
-// In all BB dominated by @dom, rewrite branches to @old into branches to @new
-static int retarget_bb(struct basic_block *dom, struct basic_block *old, struct basic_block *new)
-{
-	struct basic_block *bb;
-	int changed = 0;
-
-	if (new == old)
-		return 0;
-
-restart:
-	FOR_EACH_PTR(old->parents, bb) {
-		struct instruction *last;
-		struct multijmp *jmp;
-
-		if (!domtree_dominates(dom, bb))
-			continue;
-		last = last_instruction(bb->insns);
-		switch (last->opcode) {
-		case OP_BR:
-			changed |= rewrite_branch(bb, &last->bb_true,  old, new);
-			break;
-		case OP_CBR:
-			changed |= rewrite_branch(bb, &last->bb_true,  old, new);
-			changed |= rewrite_branch(bb, &last->bb_false, old, new);
-			break;
-		case OP_SWITCH:
-		case OP_COMPUTEDGOTO:
-			FOR_EACH_PTR(last->multijmp_list, jmp) {
-				changed |= rewrite_branch(bb, &jmp->target, old, new);
-			} END_FOR_EACH_PTR(jmp);
-			break;
-		default:
-			continue;
-		}
-
-		// since rewrite_branch() will modify old->parents() the list
-		// iteration won't work correctly. Several solution exist for
-		// this but in this case the simplest is to restart the loop.
-		goto restart;
-	} END_FOR_EACH_PTR(bb);
-	return changed;
-}
-
-static int simplify_cbr_cbr(struct instruction *insn)
-{
-	struct instruction *last;
-	struct basic_block *bot = insn->bb;
-	struct basic_block *top = bot->idom;
-	int changed = 0;
-	int trivial;
-
-	if (!top)
-		return 0;
-
-	trivial = bb_is_trivial(bot);
-	if (trivial == 0)
-		return 0;
-	if (trivial < 0)
-		return 0;
-	last = last_instruction(top->insns);
-	if (last->opcode != OP_CBR || last->cond != insn->cond)
-		return 0;
-
-	changed |= retarget_bb(last->bb_true , bot, insn->bb_true);
-	changed |= retarget_bb(last->bb_false, bot, insn->bb_false);
-	return changed;
-}
-
 /*
  * When we reach here, we have:
  *  - a basic block that ends in a conditional branch and
@@ -380,8 +276,6 @@  static int simplify_one_branch(struct basic_block *bb, struct instruction *br)
 {
 	if (simplify_phi_branch(bb, br))
 		return 1;
-	if (simplify_cbr_cbr(br))
-		return 1;
 	return simplify_branch_branch(bb, br, &br->bb_true, 1) |
 	       simplify_branch_branch(bb, br, &br->bb_false, 0);
 }