difficult on current ARM implementations for a few reasons.
1. Even though a single vmla has latency that is one cycle shorter than a pair
of vmul + vadd, a RAW hazard during the first (4? on Cortex-a8) can cause
additional pipeline stall. So it's frequently better to single codegen
vmul + vadd.
2. A vmla folowed by a vmul, vmadd, or vsub causes the second fp instruction to
stall for 4 cycles. We need to schedule them apart.
3. A vmla followed vmla is a special case. Obvious issuing back to back RAW
vmla + vmla is very bad. But this isn't ideal either:
vmul
vadd
vmla
Instead, we want to expand the second vmla:
vmla
vmul
vadd
Even with the 4 cycle vmul stall, the second sequence is still 2 cycles
faster.
Up to now, isel simply avoid codegen'ing fp vmla / vmls. This works well enough
but it isn't the optimial solution. This patch attempts to make it possible to
use vmla / vmls in cases where it is profitable.
A. Add missing isel predicates which cause vmla to be codegen'ed.
B. Make sure the fmul in (fadd (fmul)) has a single use. We don't want to
compute a fmul and a fmla.
C. Add additional isel checks for vmla, avoid cases where vmla is feeding into
fp instructions (except for the #3 exceptional case).
D. Add ARM hazard recognizer to model the vmla / vmls hazards.
E. Add a special pre-regalloc case to expand vmla / vmls when it's likely the
vmla / vmls will trigger one of the special hazards.
Work in progress, only A+B are enabled.
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instructions have to distinguish between lists of single- and double-precision
registers in order for the ASM matcher to do a proper job. In all other
respects, a list of single- or double-precision registers are the same as a list
of GPR registers.
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'db', 'ib', 'da') instead of having that mode as a separate field in the
instruction. It's more convenient for the asm parser and much more readable for
humans.
<rdar://problem/8654088>
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vldr.64 d1, [r0, #-32]
The problem was with how the addressing mode 5 encodes the offsets. This change
makes sure that the way offsets are handled in addressing mode 5 is consistent
throughout the MC code. It involves re-refactoring the "getAddrModeImmOpValue"
method into an "Imm12" and "addressing mode 5" version. But not to worry! The
majority of the duplicated code has been unified.
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with immediates up to 16-bits in size. The same logic is applied to other LDR
encodings, e.g. VLDR, but which use a different immediate bit width (8-bits in
VLDR's case). Removing the "12" allows it to be more generic.
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*_Encode classes. These instructions are the only ones which use those classes,
so a subclass isn't necessary.
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Instead of silently ignoring these instructions, emit a hard error and
force the target author to either refactor the target or mark the
instruction 'isCodeGenOnly'.
Mark a few instructions in ARM and MBlaze as isCodeGenOnly the are
doing this.
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here. The f32 in FCONSTS is handled as a double instead of a float in the
code. So the encoding of the immediate into the instruction isn't exactly in
line with the documentation in that regard. But given that we know it's handled
as a double, it doesn't cause any harm.
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to add 10+ lines to every instruction.
It may turn out that we can move this base class into it's parent class.
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