Currently when compiling for an execute-only target without movt then
EmitStructByval will generate a constant pool load which isn't
compatible with execute-only. Handle this by emitting tMOVi32imm,
and also simplify the existing movt handling by emitting t2MOVi32imm
or MOVi32imm.
Differential Revision: https://reviews.llvm.org/D154944
The expansion of the various MOVi32imm pseudo-instructions works by
splitting the operand into components (either halfwords or bytes) and
emitting instructions to combine those components into the final
result. When the operand is an immediate with some components being
zero this can result in pointless instructions that just add zero.
Avoid this by restructuring things so that a separate function handles
splitting the operand into components, then don't emit the component
if it is a zero immediate. This is straightforward for movw/movt,
where we just don't emit the movt if it's zero, but the thumb1
expansion using mov/add/lsl is more complex, as even when we don't
emit a given byte we still need to get the shift correct.
Differential Revision: https://reviews.llvm.org/D154943
Currently when compiling for an execute-only target without movt then
EmitStructByval will generate a constant pool load which isn't
compatible with execute-only. Handle this by emitting tMOVi32imm,
and also simplify the existing movt handling by emitting t2MOVi32imm
or MOVi32imm.
Differential Revision: https://reviews.llvm.org/D154944
The expansion of the various MOVi32imm pseudo-instructions works by
splitting the operand into components (either halfwords or bytes) and
emitting instructions to combine those components into the final
result. When the operand is an immediate with some components being
zero this can result in pointless instructions that just add zero.
Avoid this by restructuring things so that a separate function handles
splitting the operand into components, then don't emit the component
if it is a zero immediate. This is straightforward for movw/movt,
where we just don't emit the movt if it's zero, but the thumb1
expansion using mov/add/lsl is more complex, as even when we don't
emit a given byte we still need to get the shift correct.
Differential Revision: https://reviews.llvm.org/D154943
When we only have a 16-bit pc-relative branch instruction we generate
a table of address for a jump table. Currently this is placed inline,
but this won't work with execute-only memory. In this case generate
the jump table out-of-line.
Differential Revision: https://reviews.llvm.org/D153774
The CPSR registers ops of the instructions constructed in ExpandTMOV32BitImm
were marked as kill, instead of define. Best to use the pre-existing
t1CondCodeOp fn to construct CPSRs.
Reviewed By: simonwallis2
Differential Revision: https://reviews.llvm.org/D153763
Temporarily disabling the execute-only tests. We recently added codegen for
armv6-m, which is still in heavy development (D152795).
Disabling the tests while we're figuring out what's going on is probably the
least disruptive option, as a patch dependent on it also already landed.
[ARM] generate armv6m eXecute Only (XO) code for immediates, globals
Previously eXecute Only (XO) support was implemented for targets that support
MOVW/MOVT (~armv7+). See: https://reviews.llvm.org/D27449
XO prevents the compiler from generating data accesses to code sections. This
patch implements XO codegen for armv6-M, which does not support MOVW/MOVT, and
must resort to the following general pattern to avoid loads:
movs r3, :upper8_15:foo
lsls r3, #8
adds r3, :upper0_7:foo
lsls r3, #8
adds r3, :lower8_15:foo
lsls r3, #8
adds r3, :lower0_7:foo
ldr r3, [r3]
This is equivalent to the code pattern generated by GCC.
The above relocations are new to LLVM and have been implemented in a parent
patch: https://reviews.llvm.org/D149443.
This patch limits itself to implementing codegen for this pattern and enabling
XO for armv6-M in the backend.
Separate patches will follow for:
- switch tables
- replacing specific loads from constant islands which are spread out over the
ARM backend codebase. Amongst others: FastISel, call lowering, stack frames.
Reviewed By: john.brawn
Differential Revision: https://reviews.llvm.org/D152795
The NoMovt feature prevents the use of MOVW/MOVT
instructions on Cortex-M23 for performance reasons.
These instructions are required for execute only code
so NoMovt should be disabled when that option is enabled.
Differential Revision: https://reviews.llvm.org/D52551
llvm-svn: 343302
SHF_ARM_PURECODE flag when being built with the -mexecute-only flag.
All code sections of an ELF must have the flag set for the final .text
section to be execute-only, otherwise the flag gets removed.
A HasData flag is added to MCSection to aid in the determination that
the section is empty. A virtual setTargetSectionFlags is added to
MCELFObjectTargetWriter to allow subclasses to set target specific
section flags to be added to sections which we then use in the ARM
backend to set SHF_ARM_PURECODE.
Patch by Ivan Lozano!
Reviewed By: echristo
Differential Revision: https://reviews.llvm.org/D48792
llvm-svn: 341593
When generating table jump code for switch statements, place the jump
table label as the first operand in the various addition instructions
in order to enable addressing mode selectors to better match index
computation and possibly fold them into the addressing mode of the
table entry load instruction.
Differential revision: https://reviews.llvm.org/D39752
llvm-svn: 318033
This implements execute-only support for ARM code generation, which
prevents the compiler from generating data accesses to code sections.
The following changes are involved:
* Add the CodeGen option "-arm-execute-only" to the ARM code generator.
* Add the clang flag "-mexecute-only" as well as the GCC-compatible
alias "-mpure-code" to enable this option.
* When enabled, literal pools are replaced with MOVW/MOVT instructions,
with VMOV used in addition for floating-point literals. As the MOVT
instruction is required, execute-only support is only available in
Thumb mode for targets supporting ARMv8-M baseline or Thumb2.
* Jump tables are placed in data sections when in execute-only mode.
* The execute-only text section is assigned section ID 0, and is
marked as unreadable with the SHF_ARM_PURECODE flag with symbol 'y'.
This also overrides selection of ELF sections for globals.
llvm-svn: 289784
