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muldiv_c peepopt pass

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This commit is contained in:
Akash Levy 2024-10-15 05:29:00 -07:00
parent 8afa827b94
commit 98db6bd2d8
3 changed files with 75 additions and 0 deletions
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1
passes/pmgen/Makefile.inc
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@ -57,6 +57,7 @@ PEEPOPT_PATTERN = passes/pmgen/peepopt_shiftmul_right.pmg
PEEPOPT_PATTERN += passes/pmgen/peepopt_shiftmul_left.pmg
PEEPOPT_PATTERN += passes/pmgen/peepopt_shiftadd.pmg
PEEPOPT_PATTERN += passes/pmgen/peepopt_muldiv.pmg
PEEPOPT_PATTERN += passes/pmgen/peepopt_muldiv_c.pmg
PEEPOPT_PATTERN += passes/pmgen/peepopt_muxadd.pmg
passes/pmgen/peepopt_pm.h: passes/pmgen/pmgen.py $(PEEPOPT_PATTERN)

3
passes/pmgen/peepopt.cc
View file

@ -46,6 +46,8 @@ struct PeepoptPass : public Pass {
log("\n");
log(" * muldiv - Replace (A*B)/B with A\n");
log("\n");
log(" * muldiv_c - Replace (A*B)/C with A*(B/C) when C is a const divisible by B.\n");
log("\n");
log(" * shiftmul - Replace A>>(B*C) with A'>>(B<<K) where C and K are constants\n");
log(" and A' is derived from A by appropriately inserting padding\n");
log(" into the signal. (right variant)\n");
@ -92,6 +94,7 @@ struct PeepoptPass : public Pass {
pm.run_shiftmul_right();
pm.run_shiftmul_left();
pm.run_muldiv();
pm.run_muldiv_c();
pm.run_muxadd();
}
}

71
passes/pmgen/peepopt_muldiv_c.pmg Normal file
View file

@ -0,0 +1,71 @@
pattern muldiv_c
//
// Transforms mul->div into div->mul when b and c are divisible constants:
// y = (a * b_const) / c_const ===> a * (b_const / c_const)
//
state <SigSpec> a b_const mul_y
match mul
// Select multiplier
select mul->type == $mul
endmatch
code a b_const mul_y
printf("CODING MUL!!!\n");
// Get multiplier signals
a = port(mul, \A);
b_const = port(mul, \B);
mul_y = port(mul, \Y);
// Fanout of each multiplier Y bit should be 1 (no bit-split)
for (auto bit : mul_y)
if (nusers(bit) != 2)
reject;
// A and B can be interchanged
branch;
std::swap(a, b_const);
endcode
match div
// Select div of form (a * b_const) / c_const
select div->type == $div
index <SigSpec> port(div, \A) === port(mul, \Y)
// Check that b_const and c_const is constant
filter port(mul, \B).is_fully_const()
filter port(div, \B).is_fully_const()
endmatch
code
printf("CODING DIV!!!\n");
// Get div signals
SigSpec c_const = port(div, \B);
SigSpec div_y = port(div, \Y);
// Get properties and values of b_const and c_const
int b_const_width = mul->getParam(ID::B_WIDTH).as_int();
bool b_const_signed = mul->getParam(ID::B_SIGNED).as_bool();
bool c_const_signed = div->getParam(ID::B_SIGNED).as_bool();
int b_const_int = b_const.as_int(b_const_signed);
int c_const_int = c_const.as_int(c_const_signed);
// Check that b is divisible by c
if (b_const_int % c_const_int != 0)
reject;
// Rewire to only keep multiplier
mul->setPort(\B, Const(b_const_int / c_const_int, b_const_width));
mul->setPort(\Y, div_y);
// Remove divider
autoremove(div);
// Log, fixup, accept
log("muldiv_const pattern in %s: mul=%s, div=%s\n", log_id(module), log_id(mul), log_id(div));
mul->fixup_parameters();
accept;
endcode