From e07c2fd9d9f8270c0559a8277242439e4d409c44 Mon Sep 17 00:00:00 2001 From: Mike Pall Date: Thu, 13 Jan 2022 18:33:04 +0100 Subject: [PATCH] Fix FOLD rule for BUFHDR append. Reported by XmiliaH. (cherry-picked from commit bc1bdbf620f58f0978385828bc51272903601e17) `bufput_append()` may fold `BUFHDR RESET` + `BUFPUT` IRs to `BUFHDR APPEND` even if the right operand (`BUFSTR`) is the PHI. If it's not the last IR in the `BUFSTR` chain, this may lead to an incorrect resulting value in the buffer, which contains a longer string since `APPEND` is used instead of `RESET`. This patch adds the corresponding check inside the fold rule. Sergey Kaplun: * added the description and the test for the problem Part of tarantool/tarantool#9145 Reviewed-by: Maxim Kokryashkin Reviewed-by: Sergey Bronnikov Signed-off-by: Igor Munkin (cherry picked from commit e895818a7ac9c25c8ac07f7b79d89c66bfcefcb2) --- src/lj_opt_fold.c | 3 +- .../lj-791-fold-bufhdr-append.test.lua | 54 +++++++++++++++++++ 2 files changed, 56 insertions(+), 1 deletion(-) create mode 100644 test/tarantool-tests/lj-791-fold-bufhdr-append.test.lua diff --git a/src/lj_opt_fold.c b/src/lj_opt_fold.c index 750f1c7e53..96780fa269 100644 --- a/src/lj_opt_fold.c +++ b/src/lj_opt_fold.c @@ -584,7 +584,8 @@ LJFOLDF(bufput_append) if ((J->flags & JIT_F_OPT_FWD) && !(fleft->op2 & IRBUFHDR_APPEND) && fleft->prev == fright->op2 && - fleft->op1 == IR(fright->op2)->op1) { + fleft->op1 == IR(fright->op2)->op1 && + !(irt_isphi(fright->t) && IR(fright->op2)->prev)) { IRRef ref = fins->op1; IR(ref)->op2 = (fleft->op2 | IRBUFHDR_APPEND); /* Modify BUFHDR. */ IR(ref)->op1 = fright->op1; diff --git a/test/tarantool-tests/lj-791-fold-bufhdr-append.test.lua b/test/tarantool-tests/lj-791-fold-bufhdr-append.test.lua new file mode 100644 index 0000000000..98b83ecea4 --- /dev/null +++ b/test/tarantool-tests/lj-791-fold-bufhdr-append.test.lua @@ -0,0 +1,54 @@ +local tap = require('tap') + +-- Test file to demonstrate the incorrect LuaJIT's optimization +-- `bufput_append()` for BUFPUT IR. +-- See also https://github.com/LuaJIT/LuaJIT/issues/791. + +local test = tap.test('lj-791-fold-bufhdr-append'):skipcond({ + ['Test requires JIT enabled'] = not jit.status(), +}) + +test:plan(1) + +local EMPTY_STR = '' +local prefix = 'Lu' +local result + +jit.opt.start('hotloop=1') + +-- The interesting part of IRs is the following (non-GC64 mode): +-- 0006 str BUFSTR 0005 0003 +-- 0007 > str SLOAD #2 T +-- 0008 p32 BUFHDR [0x400004a0] RESET +-- 0009 p32 BUFPUT 0008 "Lu" +-- 0010 p32 BUFPUT 0009 0007 +-- 0011 + str BUFSTR 0010 0008 +-- 0012 + int ADD 0001 +1 +-- 0013 > int LE 0012 +5 +-- 0014 > --- LOOP ------------ +-- 0015 p32 BUFHDR [0x400004a0] RESET + +-- The instruction to be folded is the following: +-- 0016 p32 BUFPUT 0015 0011 +-- +-- The 0011 operand is PHI, which is not the last IR in the BUFSTR +-- chain (`ir->prev = REF_BIAS + 0006`). Folding this IR leads to +-- this resulting IR: +-- p32 BUFHDR 0010 APPEND +-- Which appends to buffer instead of resetting, so the resulting +-- string contains one more symbol. + +-- XXX: Use 5 iterations to run the variant part of the loop. +for _ = 1, 5 do + result = prefix .. 'a' + -- We need a non-constant string to be appended to prevent more + -- aggressive optimizations. Use an empty string for + -- convenience. Also, use a constant string in the first operand + -- in the concatenation operator for more readable `jit.dump` + -- output. + prefix = 'Lu' .. EMPTY_STR +end + +test:is(result, 'Lua', 'BUFPUT APPEND optimization is not applied for PHIs') + +test:done(true)