From: Roger Sayle Date: Tue, 31 Aug 2021 10:45:07 +0000 (+0100) Subject: Preserve SUBREG_PROMOTED_VAR_P on (extend:HI (subreg/s:QI (reg:SI))). X-Git-Tag: basepoints/gcc-13~5061 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=cad36f38576a6a781e3c62ab061c68f5b8dab13a;p=thirdparty%2Fgcc.git Preserve SUBREG_PROMOTED_VAR_P on (extend:HI (subreg/s:QI (reg:SI))). SUBREG_PROMOTED_VAR_P is a mechanism for tracking that a partial subreg is correctly zero-extended or sign-extended in the parent register. For example, the RTL (subreg/s/v:QI (reg/v:SI 23 [ x ]) 0) indicates that the byte x is zero extended in reg:SI 23, which is useful for optimization. An example is that zero extending the above QImode value to HImode can simply use a wider subreg, i.e. (subreg:HI (reg/v:SI 23 [ x ]) 0). This patch addresses the oversight/missed optimization opportunity that the new HImode subreg above should retain its SUBREG_PROMOTED_VAR_P annotation as its value is guaranteed to be correctly extended in the SImode parent. The code below to preserve SUBREG_PROMOTED_VAR_P is already present in the middle-end (e.g. simplify-rtx.c:7232-7242) but missing from one or two (precisely three) places that (accidentally) strip it. Whilst there I also added another optimization. If we need to extend the above QImode value beyond the SImode register holding it, say to DImode, we can eliminate the SUBREG and simply extend from the SImode register to DImode. 2021-08-31 Roger Sayle gcc/ChangeLog * expr.c (convert_modes): Preserve SUBREG_PROMOTED_VAR_P when creating a (wider) partial subreg from a SUBREG_PROMOTED_VAR_P subreg. * simplify-rtx.c (simplify_unary_operation_1) [SIGN_EXTEND]: Likewise, preserve SUBREG_PROMOTED_VAR_P when creating a (wider) partial subreg from a SUBREG_PROMOTED_VAR_P subreg. Generate SIGN_EXTEND of the SUBREG_REG when a subreg would be paradoxical. [ZERO_EXTEND]: Likewise, preserve SUBREG_PROMOTED_VAR_P when creating a (wider) partial subreg from a SUBREG_PROMOTED_VAR_P subreg. Generate ZERO_EXTEND of the SUBREG_REG when a subreg would be paradoxical. --- diff --git a/gcc/expr.c b/gcc/expr.c index 096c0315ecc9..5dd98a9bccc9 100644 --- a/gcc/expr.c +++ b/gcc/expr.c @@ -688,7 +688,24 @@ convert_modes (machine_mode mode, machine_mode oldmode, rtx x, int unsignedp) && (GET_MODE_PRECISION (subreg_promoted_mode (x)) >= GET_MODE_PRECISION (int_mode)) && SUBREG_CHECK_PROMOTED_SIGN (x, unsignedp)) - x = gen_lowpart (int_mode, SUBREG_REG (x)); + { + scalar_int_mode int_orig_mode; + machine_mode orig_mode = GET_MODE (x); + x = gen_lowpart (int_mode, SUBREG_REG (x)); + + /* Preserve SUBREG_PROMOTED_VAR_P if the new mode is wider than + the original mode, but narrower than the inner mode. */ + if (GET_CODE (x) == SUBREG + && GET_MODE_PRECISION (subreg_promoted_mode (x)) + > GET_MODE_PRECISION (int_mode) + && is_a (orig_mode, &int_orig_mode) + && GET_MODE_PRECISION (int_mode) + > GET_MODE_PRECISION (int_orig_mode)) + { + SUBREG_PROMOTED_VAR_P (x) = 1; + SUBREG_PROMOTED_SET (x, unsignedp); + } + } if (GET_MODE (x) != VOIDmode) oldmode = GET_MODE (x); diff --git a/gcc/simplify-rtx.c b/gcc/simplify-rtx.c index e431e0c19d7f..ebad5cb5a79c 100644 --- a/gcc/simplify-rtx.c +++ b/gcc/simplify-rtx.c @@ -1512,12 +1512,28 @@ simplify_context::simplify_unary_operation_1 (rtx_code code, machine_mode mode, target mode is the same as the variable's promotion. */ if (GET_CODE (op) == SUBREG && SUBREG_PROMOTED_VAR_P (op) - && SUBREG_PROMOTED_SIGNED_P (op) - && !paradoxical_subreg_p (mode, GET_MODE (SUBREG_REG (op)))) + && SUBREG_PROMOTED_SIGNED_P (op)) { - temp = rtl_hooks.gen_lowpart_no_emit (mode, SUBREG_REG (op)); - if (temp) - return temp; + rtx subreg = SUBREG_REG (op); + machine_mode subreg_mode = GET_MODE (subreg); + if (!paradoxical_subreg_p (mode, subreg_mode)) + { + temp = rtl_hooks.gen_lowpart_no_emit (mode, subreg); + if (temp) + { + /* Preserve SUBREG_PROMOTED_VAR_P. */ + if (partial_subreg_p (temp)) + { + SUBREG_PROMOTED_VAR_P (temp) = 1; + SUBREG_PROMOTED_SET (temp, 1); + } + return temp; + } + } + else + /* Sign-extending a sign-extended subreg. */ + return simplify_gen_unary (SIGN_EXTEND, mode, + subreg, subreg_mode); } /* (sign_extend:M (sign_extend:N )) is (sign_extend:M ). @@ -1631,12 +1647,28 @@ simplify_context::simplify_unary_operation_1 (rtx_code code, machine_mode mode, target mode is the same as the variable's promotion. */ if (GET_CODE (op) == SUBREG && SUBREG_PROMOTED_VAR_P (op) - && SUBREG_PROMOTED_UNSIGNED_P (op) - && !paradoxical_subreg_p (mode, GET_MODE (SUBREG_REG (op)))) + && SUBREG_PROMOTED_UNSIGNED_P (op)) { - temp = rtl_hooks.gen_lowpart_no_emit (mode, SUBREG_REG (op)); - if (temp) - return temp; + rtx subreg = SUBREG_REG (op); + machine_mode subreg_mode = GET_MODE (subreg); + if (!paradoxical_subreg_p (mode, subreg_mode)) + { + temp = rtl_hooks.gen_lowpart_no_emit (mode, subreg); + if (temp) + { + /* Preserve SUBREG_PROMOTED_VAR_P. */ + if (partial_subreg_p (temp)) + { + SUBREG_PROMOTED_VAR_P (temp) = 1; + SUBREG_PROMOTED_SET (temp, 0); + } + return temp; + } + } + else + /* Zero-extending a zero-extended subreg. */ + return simplify_gen_unary (ZERO_EXTEND, mode, + subreg, subreg_mode); } /* Extending a widening multiplication should be canonicalized to