This patch teaches i386's STV pass how to handle SUBREG conversions, i.e. that a TImode SUBREG can be transformed into a V1TImode SUBREG, without worrying about other DEFs and USEs.
A motivating example where this is useful is typedef long long __m128i __attribute__ ((__vector_size__ (16))); int foo (__m128i x, __m128i y) { return (__int128)x == (__int128)y; } where with -O2 -msse4 we can now scalar-to-vector transform: (insn 7 4 8 2 (set (reg:CCZ 17 flags) (compare:CCZ (subreg:TI (reg/v:V2DI 86 [ x ]) 0) (subreg:TI (reg/v:V2DI 87 [ y ]) 0))) {*cmpti_doubleword} into (insn 17 4 7 2 (set (reg:V1TI 91) (xor:V1TI (subreg:V1TI (reg/v:V2DI 86 [ x ]) 0) (subreg:V1TI (reg/v:V2DI 87 [ y ]) 0))) (nil)) (insn 7 17 8 2 (set (reg:CCZ 17 flags) (unspec:CCZ [ (reg:V1TI 91) repeated x2 ] UNSPEC_PTEST)) {*sse4_1_ptestv1ti} (expr_list:REG_DEAD (reg/v:V2DI 87 [ y ]) (expr_list:REG_DEAD (reg/v:V2DI 86 [ x ]) (nil)))) with the dramatic effect that the assembly output before: foo: movaps %xmm0, -40(%rsp) movq -32(%rsp), %rdx movq %xmm0, %rax movq %xmm1, %rsi movaps %xmm1, -24(%rsp) movq -16(%rsp), %rcx xorq %rsi, %rax xorq %rcx, %rdx orq %rdx, %rax sete %al movzbl %al, %eax ret now becomes foo: pxor %xmm1, %xmm0 xorl %eax, %eax ptest %xmm0, %xmm0 sete %al ret i.e. a 128-bit vector doesn't need to be transferred to the scalar unit to be tested for equality. The new test case includes additional related examples that show similar improvements. Previously we explicitly checked *cmpti_doubleword operands to be either immediate constants, or a TImode REG or a TImode MEM. By enhancing this to allow a TImode SUBREG, we now handle everything that would match the general_operand predicate, making this part of STV more like other RTL passes (lra/reload). The big change is that unlike a regular DF USE, a SUBREG USE doesn't require us to analyze and convert the rest of the DEF-USE chain. This patch has been tested on x86_64-pc-linux-gnu with make bootstrap and make -k check, both with and without --target_board=unix{-m32} with no new failures. Ok for mainline? 2023-06-24 Roger Sayle <ro...@nextmovesoftware.com> gcc/ChangeLog * config/i386/i386-features.cc (scalar_chain:add_insn): Don't call analyze_register_chain if the USE is a SUBREG. (timode_scalar_chain::convert_op): Call gen_lowpart to convert TImode SUBREGs to V1TImode SUBREGs. (convertible_comparison_p): We can now handle all general_operands of *cmp<dwi>_doubleword. (timode_remove_non_convertible_regs): We only need to check TImode uses that aren't TImode SUBREGs of registers in other modes. gcc/testsuite/ChangeLog * gcc.target/i386/sse4_1-ptest-7.c: New test case. Thanks in advance, Roger --
diff --git a/gcc/config/i386/i386-features.cc b/gcc/config/i386/i386-features.cc index 4a3b07a..6e9ba54 100644 --- a/gcc/config/i386/i386-features.cc +++ b/gcc/config/i386/i386-features.cc @@ -449,7 +449,8 @@ scalar_chain::add_insn (bitmap candidates, unsigned int insn_uid, return true; for (ref = DF_INSN_UID_USES (insn_uid); ref; ref = DF_REF_NEXT_LOC (ref)) - if (!DF_REF_REG_MEM_P (ref)) + if (DF_REF_TYPE (ref) == DF_REF_REG_USE + && !SUBREG_P (DF_REF_REG (ref))) if (!analyze_register_chain (candidates, ref, disallowed)) return false; @@ -1621,7 +1622,8 @@ timode_scalar_chain::convert_op (rtx *op, rtx_insn *insn) else { gcc_assert (SUBREG_P (*op)); - gcc_assert (GET_MODE (*op) == vmode); + if (GET_MODE (*op) != V1TImode) + *op = gen_lowpart (V1TImode, *op); } } @@ -1912,12 +1914,8 @@ convertible_comparison_p (rtx_insn *insn, enum machine_mode mode) rtx op2 = XEXP (src, 1); /* *cmp<dwi>_doubleword. */ - if ((CONST_SCALAR_INT_P (op1) - || ((REG_P (op1) || MEM_P (op1)) - && GET_MODE (op1) == mode)) - && (CONST_SCALAR_INT_P (op2) - || ((REG_P (op2) || MEM_P (op2)) - && GET_MODE (op2) == mode))) + if (general_operand (op1, mode) + && general_operand (op2, mode)) return true; /* *testti_doubleword. */ @@ -2244,8 +2242,9 @@ timode_remove_non_convertible_regs (bitmap candidates) DF_REF_REGNO (ref)); FOR_EACH_INSN_USE (ref, insn) - if (!DF_REF_REG_MEM_P (ref) - && GET_MODE (DF_REF_REG (ref)) == TImode) + if (DF_REF_TYPE (ref) == DF_REF_REG_USE + && GET_MODE (DF_REF_REG (ref)) == TImode + && !SUBREG_P (DF_REF_REG (ref))) timode_check_non_convertible_regs (candidates, regs, DF_REF_REGNO (ref)); } diff --git a/gcc/testsuite/gcc.target/i386/sse4_1-ptest-7.c b/gcc/testsuite/gcc.target/i386/sse4_1-ptest-7.c new file mode 100644 index 0000000..bb52d3b --- /dev/null +++ b/gcc/testsuite/gcc.target/i386/sse4_1-ptest-7.c @@ -0,0 +1,22 @@ +/* { dg-do compile { target int128 } } */ +/* { dg-options "-O2 -msse4.1" } */ + +typedef long long __m128i __attribute__ ((__vector_size__ (16))); + +int foo (__m128i x, __m128i y) +{ + return (__int128)x == (__int128)y; +} + +int bar (__m128i x, __m128i y) +{ + return (__int128)(x^y) == 0; +} + +int baz (__m128i x, __m128i y) +{ + return (__int128)(x==y) == ~0; +} + +/* { dg-final { scan-assembler-times "ptest\[ \\t\]+%" 3 } } */ +/* { dg-final { scan-assembler-not "%\[er\]sp" } } */