1957bedf29
Consider creating a polarity-reversed mask from a set-bit (i.e., if
the bit is set, produce all-ones; otherwise: all-zeros). Using Zbb,
this can be expressed as bexti, followed by an addi of minus-one. To
enable the combiner to discover this opportunity, we need to split the
canonical expression for "(a & (1 << BIT_NO)) ? 0 : -1" into a form
combinable into bexti.
Consider the function:
long f(long a)
{
return (a & (1 << BIT_NO)) ? 0 : -1;
}
This produces the following sequence prior to this change:
andi a0,a0,16
seqz a0,a0
neg a0,a0
ret
Following this change, it results in:
bexti a0,a0,4
addi a0,a0,-1
ret
gcc/ChangeLog:
* config/riscv/bitmanip.md: Add a splitter to generate
polarity-reversed masks from a set bit using bexti + addi.
gcc/testsuite/ChangeLog:
* gcc.target/riscv/zbs-bexti.c: New test.
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