From 48eb2ca449b7f8e8e0684a2d92c8a1d0224861da Mon Sep 17 00:00:00 2001 From: Luc Van Oostenryck Date: Sun, 18 Apr 2021 00:45:43 +0200 Subject: canonicalize constant signed compares toward zero Currently, signed compares against a constant are canonicalized toward the smallest possible constant. So, the following canonicalization are done: x < 256 --> x <= 255 x < -2047 --> x <= -2048 This has two advantages: 1) it maximalizes the number of constants possible for a given bit size. 2) it allows to remove all < and all >= But it has also a serious disadvantages: a simple comparison against zero, like: x >= 0 is canonicalized into: x > -1 Which can be more costly for some architectures if translated as such , is also less readable than the version using 0 and is also sometimes quite more complicated to match in some simplification patterns. So, canonicalize it using 'towards 0' / using the smallest constant in absolute value. Signed-off-by: Luc Van Oostenryck --- simplify.c | 34 +++++++++++++--- validation/optim/canonical-cmp-zero.c | 74 +++++++++++++++++++++++++++++++++++ 2 files changed, 102 insertions(+), 6 deletions(-) create mode 100644 validation/optim/canonical-cmp-zero.c diff --git a/simplify.c b/simplify.c index 9e3514d8..e0e4f9eb 100644 --- a/simplify.c +++ b/simplify.c @@ -1178,38 +1178,52 @@ static int simplify_compare_constant(struct instruction *insn, long long value) switch (insn->opcode) { case OP_SET_LT: + if (!value) + break; if (value == sign_bit(size)) // (x < SMIN) --> 0 return replace_with_pseudo(insn, value_pseudo(0)); if (value == sign_mask(size)) // (x < SMAX) --> (x != SMAX) return replace_opcode(insn, OP_SET_NE); if (value == sign_bit(size) + 1)// (x < SMIN + 1) --> (x == SMIN) return replace_binop_value(insn, OP_SET_EQ, sign_bit(size)); - changed |= replace_binop_value(insn, OP_SET_LE, (value - 1) & bits); + if (!(value & sign_bit(size))) + changed |= replace_binop_value(insn, OP_SET_LE, (value - 1) & bits); break; case OP_SET_LE: + if (!value) + break; if (value == sign_mask(size)) // (x <= SMAX) --> 1 return replace_with_pseudo(insn, value_pseudo(1)); if (value == sign_bit(size)) // (x <= SMIN) --> (x == SMIN) return replace_opcode(insn, OP_SET_EQ); if (value == sign_mask(size) - 1) // (x <= SMAX - 1) --> (x != SMAX) return replace_binop_value(insn, OP_SET_NE, sign_mask(size)); + if (value & sign_bit(size)) + changed |= replace_binop_value(insn, OP_SET_LT, (value + 1) & bits); break; case OP_SET_GE: + if (!value) + break; if (value == sign_bit(size)) // (x >= SMIN) --> 1 return replace_with_pseudo(insn, value_pseudo(1)); if (value == sign_mask(size)) // (x >= SMAX) --> (x == SMAX) return replace_opcode(insn, OP_SET_EQ); if (value == sign_bit(size) + 1)// (x >= SMIN + 1) --> (x != SMIN) return replace_binop_value(insn, OP_SET_NE, sign_bit(size)); - changed |= replace_binop_value(insn, OP_SET_GT, (value - 1) & bits); + if (!(value & sign_bit(size))) + changed |= replace_binop_value(insn, OP_SET_GT, (value - 1) & bits); break; case OP_SET_GT: + if (!value) + break; if (value == sign_mask(size)) // (x > SMAX) --> 0 return replace_with_pseudo(insn, value_pseudo(0)); if (value == sign_bit(size)) // (x > SMIN) --> (x != SMIN) return replace_opcode(insn, OP_SET_NE); if (value == sign_mask(size) - 1) // (x > SMAX - 1) --> (x == SMAX) return replace_binop_value(insn, OP_SET_EQ, sign_mask(size)); + if (value & sign_bit(size)) + changed |= replace_binop_value(insn, OP_SET_GE, (value + 1) & bits); break; case OP_SET_B: @@ -1271,8 +1285,10 @@ static int simplify_compare_constant(struct instruction *insn, long long value) if ((value & bits) != value) return replace_with_value(insn, 1); break; - case OP_SET_LE: + case OP_SET_LE: case OP_SET_LT: value = sign_extend(value, def->size); + if (insn->opcode == OP_SET_LT) + value -= 1; if (bits & sign_bit(def->size)) break; if (value < 0) @@ -1282,8 +1298,10 @@ static int simplify_compare_constant(struct instruction *insn, long long value) if (value == 0) return replace_opcode(insn, OP_SET_EQ); break; - case OP_SET_GT: + case OP_SET_GT: case OP_SET_GE: value = sign_extend(value, def->size); + if (insn->opcode == OP_SET_GE) + value -= 1; if (bits & sign_bit(def->size)) break; if (value < 0) @@ -1340,16 +1358,20 @@ static int simplify_compare_constant(struct instruction *insn, long long value) if (bits >= value) return replace_with_value(insn, 1); break; + case OP_SET_LT: + value -= 1; case OP_SET_LE: - value = sign_extend(value, def->size); if (bits & sign_bit(def->size)) { + value = sign_extend(value, def->size); if (value >= -1) return replace_with_value(insn, 1); } break; + case OP_SET_GE: + value -= 1; case OP_SET_GT: - value = sign_extend(value, def->size); if (bits & sign_bit(def->size)) { + value = sign_extend(value, def->size); if (value >= -1) return replace_with_value(insn, 0); } diff --git a/validation/optim/canonical-cmp-zero.c b/validation/optim/canonical-cmp-zero.c new file mode 100644 index 00000000..e01a00e6 --- /dev/null +++ b/validation/optim/canonical-cmp-zero.c @@ -0,0 +1,74 @@ +int f00(int x) { return x >= 0; } +int f01(int x) { return x > -1; } +int f02(int x) { return x < 1; } +int f03(int x) { return x <= 0; } + +int f10(int x) { return x < 16; } +int f11(int x) { return x <= 15; } + +int f20(int x) { return x > -9; } +int f21(int x) { return x >= -8; } + +/* + * check-name: canonical-cmp-zero + * check-command: test-linearize -Wno-decl $file + * + * check-output-start +f00: +.L0: + + setge.32 %r2 <- %arg1, $0 + ret.32 %r2 + + +f01: +.L2: + + setge.32 %r5 <- %arg1, $0 + ret.32 %r5 + + +f02: +.L4: + + setle.32 %r8 <- %arg1, $0 + ret.32 %r8 + + +f03: +.L6: + + setle.32 %r11 <- %arg1, $0 + ret.32 %r11 + + +f10: +.L8: + + setle.32 %r14 <- %arg1, $15 + ret.32 %r14 + + +f11: +.L10: + + setle.32 %r17 <- %arg1, $15 + ret.32 %r17 + + +f20: +.L12: + + setge.32 %r20 <- %arg1, $0xfffffff8 + ret.32 %r20 + + +f21: +.L14: + + setge.32 %r23 <- %arg1, $0xfffffff8 + ret.32 %r23 + + + * check-output-end + */ -- cgit 1.2.3-korg