the generated FastISel. X86 doesn't need to generate code to match ADD16ri8
since ADD16ri will do just fine. This is a small codesize win in the generated
instruction selector.
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value constraints on them (when defined as ImmLeaf's). This is particularly important
for X86-64, where almost all reg/imm instructions take a i64immSExt32 immediate operand,
which has a value constraint. Before this patch we ended up iseling the examples into
such amazing code as:
movabsq $7, %rax
imulq %rax, %rdi
movq %rdi, %rax
ret
now we produce:
imulq $7, %rdi, %rax
ret
This dramatically shrinks the generated code at -O0 on x86-64.
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simplifying them and exposing more information to tblgen. It would be nice
if other target authors adopted this as well, particularly arm since it has fastisel.
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kind of predicate: one that is specific to imm nodes. The predicate function
specified here just checks an int64_t directly instead of messing around with
SDNode's. The virtue of this is that it means that fastisel and other things
can reason about these predicates.
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structure and fix some fixmes. We now have a TreePredicateFn class
that handles all of the decoding of these things. This is an internal
cleanup that has no impact on the code generated by tblgen.
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2. implement rdar://9289501 - fast isel should fold trivial multiplies to shifts
3. teach tblgen to handle shift immediates that are different sizes than the
shifted operands, eliminating some code from the X86 fast isel backend.
4. Have FastISel::SelectBinaryOp use (the poorly named) FastEmit_ri_ function
instead of FastEmit_ri to simplify code.
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when we have a global variable base an an index. Instead, just give up on
folding the global variable.
Before we'd geenrate:
_test: ## @test
## BB#0:
movq _rtx_length@GOTPCREL(%rip), %rax
leaq (%rax), %rax
addq %rdi, %rax
movzbl (%rax), %eax
ret
now we generate:
_test: ## @test
## BB#0:
movq _rtx_length@GOTPCREL(%rip), %rax
movzbl (%rax,%rdi), %eax
ret
The difference is even more significant when there is a scale
involved.
This fixes rdar://9289558 - total fail with addr mode formation at -O0/x86-64
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less trivial things) into a dummy lea. Before we generated:
_test: ## @test
movq _G@GOTPCREL(%rip), %rax
leaq (%rax), %rax
ret
now we produce:
_test: ## @test
movq _G@GOTPCREL(%rip), %rax
ret
This is part of rdar://9289558
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The basic issue here is that bottom-up isel is matching the branch
and compare, and was failing to fold the load into the branch/compare
combo. Fixing this (by allowing folding into any instruction of a
sequence that is selected) allows us to produce things like:
cmpb $0, 52(%rax)
je LBB4_2
instead of:
movb 52(%rax), %cl
cmpb $0, %cl
je LBB4_2
This makes the generated -O0 code run a bit faster, but also speeds up
compile time by putting less pressure on the register allocator and
generating less code.
This was one of the biggest classes of missing load folding. Implementing
this shrinks 176.gcc's c-decl.s (as a random example) by about 4% in (verbose-asm)
line count.
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which don't need to check for falling off the end of a block *and* end of phi
nodes, since terminators are never phis.
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Returning a new node makes the code try to replace the old node, which
in the included testcase is killed by CSE.
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Break the arc-profile code out to a function like the notes emission code is,
and reorder the functions in the file.
The only functionality change is that we no longer modify the Module when the
Module has no debug info to use.
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does. Also mostly implement it. Still a work-in-progress, but generates legal
output on crafted test cases.
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