On Mon, Jul 7, 2014 at 8:55 AM, Kugan <kugan.vivekanandara...@linaro.org> wrote: >> For -fwrapv I don't see why you'd get into trouble ever, the VRP computation >> should be well aware of the -fwrapv semantics and the value ranges should >> reflect that. >> >> For -fno-strict-overflow, I have no idea since it is very weirdly defined. >> >> In any case, for your example above, the loop is always well defined, >> because for char/short a++ is performed as: >> a = (short) ((int) a + 1) >> So, if the patch turns it into infinite loop, with -Os -fno-strict-overflow >> or -Os, it is simply a problem with the patch. VR [1, 32768] looks correct, >> a++ is performed only if a is >= 0, therefore before addition [0, 32767]. >> But from VR [1, 32768] you can't optimize away the sign extension, make sure >> you don't have there off-by-one?
I have fixed the above bug yesterday. >> It would be nice if the patch contained some testcases, it is easy >> to construct testcases where you have arbitrary VRs on some SSA_NAMEs, >> you just need something to stick the VR on, so you can do something like: >> type foo (type a) >> { >> if (a < VR_min + 1 || a > VR_max + 1) return; // If VR_min is type minimum >> or VR_max type maximum this needs to be adjusted of course. >> a = a + 1; >> // now you can try some cast that your optimization would try to optimize >> return a; >> } >> Or void bar (type a) { a = (a & mask) + bias; (or similarly) } >> Make sure to cover the boundary cases, where VR minimum or maximum still >> allow optimizing away zero and/or sign extensions, and another case where >> they are +- 1 and already don't allow it. > > > Hi Jakub, > > For -fwrapv, it is due to how PROMOTE_MODE is defined in arm back-end. > In the test-case, a function (which has signed char return type) returns > -1 in one of the paths. ARM PROMOTE_MODE changes that to 255 and relies > on zero/sign extension generated by RTL again for the correct value. I > saw some other targets also defining similar think. I am therefore > skipping removing zero/sign extension if the ssa variable can be set to > negative integer constants. Hm? I think you should rather check that you are removing a sign-/zero-extension - PROMOTE_MODE tells you if it will sign- or zero-extend. Definitely + /* In some architectures, negative integer constants are truncated and + sign changed with target defined PROMOTE_MODE macro. This will impact + the value range seen here and produce wrong code if zero/sign extensions + are eliminated. Therefore, return false if this SSA can have negative + integers. */ + if (is_gimple_assign (stmt) + && (TREE_CODE_CLASS (gimple_assign_rhs_code (stmt)) == tcc_unary)) + { + tree rhs1 = gimple_assign_rhs1 (stmt); + if (TREE_CODE (rhs1) == INTEGER_CST + && !TYPE_UNSIGNED (TREE_TYPE (ssa)) + && tree_int_cst_compare (rhs1, integer_zero_node) == -1) + return false; looks completely bogus ... (an unary op with a constant operand?) instead you want to do sth like mode = TYPE_MODE (TREE_TYPE (ssa)); rhs_uns = TYPE_UNSIGNED (TREE_TYPE (ssa)); PROMOTE_MODE (mode, rhs_uns, TREE_TYPE (ssa)); instead of initializing rhs_uns from ssas type. That is, if PROMOTE_MODE tells you to promote _not_ according to ssas sign then honor that. > As for the -fno-strict-overflow case, if the variables overflows, in VRP > dumps, I see +INF(OVF), but the value range stored in ssa has TYPE_MAX. > We therefore should limit the comparison to (TYPE_MIN < VR_MIN && VR_MAX > < TYPE_MAX) instead of (TYPE_MIN <= VR_MIN && VR_MAX <= TYPE_MAX) when > checking to be sure that this is not the overflowing case. Attached > patch changes this. I don't think that's necessary - the overflow cases happen only when that overflow has undefined behavior, thus any valid program will have values <= MAX. Richard. > I have bootstrapped on x86_64-unknown-linux-gnu and regression tested > for x86_64-unknown-linux-gnu, arm-none-linux-gnueabi (using qemu), > aarch64_be-none-elf (Foundation model), aarch64-none-elf > --with-abi=ilp32 (Foundation model) and s390x-ibm-linux (64bit, using > qemu) with no new regression. > > Is this OK? > > Thanks, > Kugan > > gcc/ > 2014-07-07 Kugan Vivekanandarajah <kug...@linaro.org> > > * calls.c (precompute_arguments): Check is_promoted_for_type > and set the promoted mode. > (is_promoted_for_type): New function. > (expand_expr_real_1): Check is_promoted_for_type > and set the promoted mode. > * expr.h (is_promoted_for_type): New function definition. > * cfgexpand.c (expand_gimple_stmt_1): Call emit_move_insn if > SUBREG is promoted with SRP_SIGNED_AND_UNSIGNED. > > > gcc/testsuite > > 2014-07-07 Kugan Vivekanandarajah <kug...@linaro.org> > > * gcc.dg/zero_sign_ext_test.c: New test.