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[Valgrind-developers] [valgrind/jit-hacks-2] Implement If-Then-Else leg lifting if the condition is a constant.
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From: Ivo R. <ir...@so...> - 2017-09-29 20:58:35
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https://sourceware.org/git/gitweb.cgi?p=valgrind.git;h=3c769fb56e06095b906ad8be8b4521bb9366d25f commit 3c769fb56e06095b906ad8be8b4521bb9366d25f Author: Ivo Raisr <iv...@iv...> Date: Fri Sep 29 22:57:15 2017 +0200 Implement If-Then-Else leg lifting if the condition is a constant. Diff: --- VEX/priv/ir_opt.c | 78 ++++++++++++++++++++++++++++++++++++------------------- 1 file changed, 52 insertions(+), 26 deletions(-) diff --git a/VEX/priv/ir_opt.c b/VEX/priv/ir_opt.c index 6939776..fe1a345 100644 --- a/VEX/priv/ir_opt.c +++ b/VEX/priv/ir_opt.c @@ -2677,13 +2677,16 @@ static void subst_and_fold_PhiNodes(SubstEnv* env, IRStmtVec* stmts, } } -static IRStmtVec* subst_and_fold_Stmts(SubstEnv* env, IRStmtVec* in); +static IRStmtVec* subst_and_fold_StmtVec(SubstEnv* env, IRStmtVec* in); +static void subst_and_fold_Stmts(SubstEnv* env, IRStmtVec* in, + UInt fixups[], UInt *n_fixups); /* Apply the subst to stmt, then fold the result as much as possible. Much simplified due to stmt being previously flattened. As a result of this, the stmt may wind up being turned into a no-op. */ -static IRStmt* subst_and_fold_Stmt(SubstEnv* env, IRStmt* st) +static IRStmt* subst_and_fold_Stmt(SubstEnv* env, IRStmt* st, IRStmtVec* parent, + UInt fixups[], UInt *n_fixups) { # if 0 vex_printf("\nsubst and fold stmt\n"); @@ -2892,37 +2895,52 @@ static IRStmt* subst_and_fold_Stmt(SubstEnv* env, IRStmt* st) vassert(isIRAtom(ite->cond)); IRExpr *fcond = fold_Expr(env, subst_Expr(env, ite->cond)); if (fcond->tag == Iex_Const) { + IRStmtVec* remaining_leg; /* Interesting. The condition on this "if-then-else" has folded down to a constant. */ vassert(fcond->Iex.Const.con->tag == Ico_U1); if (fcond->Iex.Const.con->Ico.U1 == True) { - /* TODO-JIT: "else" leg is never going to happen, so dump it. */ if (vex_control.iropt_verbosity > 0) vex_printf("vex iropt: IRStmt_IfThenElse became " "unconditional\n"); + /* "else" leg is never going to happen, so dump it. */ + remaining_leg = ite->then_leg; } else { vassert(fcond->Iex.Const.con->Ico.U1 == False); - /* TODO-JIT: "then" leg is never going to happen, so dump it. */ if (vex_control.iropt_verbosity > 0) vex_printf("vex iropt: IRStmt_IfThenElse became " "unconditional\n"); + /* "then" leg is never going to happen, so dump it. */ + remaining_leg = ite->else_leg; } - /* TODO-JIT: Pull the only remaining leg into the current IRStmtVec. - Here is what needs to be done: - 1. Rewrite ID of all IRTemp's (in tyenv->ids) defined in the - pulled leg. These are tracked in leg's defset. - 2. Insert all statements from the leg in the env->stmts_out - at the current position. */ - vpanic("IfThenElse leg lifting unimplemented"); + + /* Now pull the only remaining leg into the current IRStmtVec. */ + /* 1. Pull all IRTemp's defined in the remaining leg into parent's + defset. */ + const IRTempDefSet* defset = remaining_leg->defset; + for (UInt slot = 0; slot < defset->slots_used; slot++) { + UInt slot_value = defset->set[slot]; + for (UInt bit = 0; bit < BITS_PER_SLOT; bit++) { + if (slot_value & (1 << bit)) { + IRTemp tmp = slot * BITS_PER_SLOT + bit; + setIRTempDefined(parent->defset, tmp); + } + } + } + + /* 2. Process now all statements from the remaining leg as if they + were at the current position in the input IRStmtVec. */ + subst_and_fold_Stmts(env, remaining_leg, fixups, n_fixups); + return IRStmt_NoOp(); // return no-op; it will be removed anyway } SubstEnv* then_env = newSubstEnv(env->tyenv, ite->then_leg, env); - IRStmtVec* then_stmts = subst_and_fold_Stmts(then_env, ite->then_leg); + IRStmtVec* then_stmts = subst_and_fold_StmtVec(then_env, ite->then_leg); subst_and_fold_PhiNodes(then_env, then_stmts, True /* srcThen */, ite->phi_nodes); SubstEnv* else_env = newSubstEnv(env->tyenv, ite->else_leg, env); - IRStmtVec* else_stmts = subst_and_fold_Stmts(else_env, ite->else_leg); + IRStmtVec* else_stmts = subst_and_fold_StmtVec(else_env, ite->else_leg); subst_and_fold_PhiNodes(else_env, else_stmts, False /* srcThen */, ite->phi_nodes); @@ -2936,15 +2954,10 @@ static IRStmt* subst_and_fold_Stmt(SubstEnv* env, IRStmt* st) } } -/* Is to be called with already created SubstEnv as per newSubstEnv(). */ -static IRStmtVec* subst_and_fold_Stmts(SubstEnv* env, IRStmtVec* in) +#define N_FIXUPS 16 +static void subst_and_fold_Stmts(SubstEnv* env, IRStmtVec* in, + UInt fixups[], UInt *n_fixups) { - /* Keep track of IRStmt_LoadGs that we need to revisit after - processing all the other statements. */ - const Int N_FIXUPS = 16; - Int fixups[N_FIXUPS]; /* indices in the stmt array of 'out' */ - Int n_fixups = 0; - IRStmtVec* out = env->stmts; /* For each original SSA-form stmt ... */ @@ -2960,7 +2973,7 @@ static IRStmtVec* subst_and_fold_Stmts(SubstEnv* env, IRStmtVec* in) /* perhaps st2 is already a no-op? */ if (st2->tag == Ist_NoOp) continue; - st2 = subst_and_fold_Stmt(env, st2); + st2 = subst_and_fold_Stmt(env, st2, in, fixups, n_fixups); /* Deal with some post-folding special cases. */ switch (st2->tag) { @@ -3009,9 +3022,9 @@ static IRStmtVec* subst_and_fold_Stmts(SubstEnv* env, IRStmtVec* in) into a load-convert pair. The fixups[] entry refers to the inserted NoOp, and we expect to find the relevant LoadG immediately after it. */ - vassert(n_fixups >= 0 && n_fixups <= N_FIXUPS); - if (n_fixups < N_FIXUPS) { - fixups[n_fixups++] = out->stmts_used; + vassert(*n_fixups >= 0 && *n_fixups <= N_FIXUPS); + if (*n_fixups < N_FIXUPS) { + fixups[*n_fixups++] = out->stmts_used; addStmtToIRStmtVec(out, IRStmt_NoOp()); } } @@ -3026,6 +3039,18 @@ static IRStmtVec* subst_and_fold_Stmts(SubstEnv* env, IRStmtVec* in) /* Not interesting, copy st2 into the output vector. */ addStmtToIRStmtVec(out, st2); } +} + +/* Is to be called with already created SubstEnv as per newSubstEnv(). */ +static IRStmtVec* subst_and_fold_StmtVec(SubstEnv* env, IRStmtVec* in) +{ + /* Keep track of IRStmt_LoadGs that we need to revisit after + processing all the other statements. */ + UInt fixups[N_FIXUPS]; /* indices in the stmt array of 'out' */ + UInt n_fixups = 0; + + IRStmtVec* out = env->stmts; + subst_and_fold_Stmts(env, in, fixups, &n_fixups); /* Process any leftover unconditional LoadGs that we noticed in the main pass. */ @@ -3074,13 +3099,14 @@ static IRStmtVec* subst_and_fold_Stmts(SubstEnv* env, IRStmtVec* in) return out; } +#undef N_FIXUPS IRSB* cprop_BB ( IRSB* in ) { SubstEnv* env = newSubstEnv(in->tyenv, in->stmts, NULL); IRSB* out = emptyIRSB(); out->tyenv = deepCopyIRTypeEnv(in->tyenv); - out->stmts = subst_and_fold_Stmts(env, in->stmts); + out->stmts = subst_and_fold_StmtVec(env, in->stmts); out->id_seq = in->id_seq; out->next = subst_Expr( env, in->next ); out->jumpkind = in->jumpkind; |
