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With FP arithmetic, the negation of "x < y" is not "x >= y". For this reason, the back-end intermediate languages of CompCert used to have both "Ccompf c" and "Cnotcompf c" comparison operators, where "c" is of type Integers.comparison and "Cnotcompf c" denotes the negation of FP comparison c.
There are some problems with this approach:
- Beyond Cnotcompf we also need Cnotcompfs (for single precision FP) and, in case of ARM, special forms for not-comparison against 0.0. This duplication of comparison constructors inevitably causes some code and proof duplication.
- Cnotcompf Ceq is really Ccompf Cne, and likewise Cnotcompf Cne is really Ccompf Ceq, hence the representation of FP comparisons is not canonical, adding to the code and proof duplication mentioned above.
- Cnotcompf is introduced in CminorSel, but in Cminor we don't have it, making it impossible to express some transformations over comparisons at the machine-independent Cminor level.
This commit develops an alternate approach, whereas FP comparisons have their own type, defined as Floats.fp_comparison, and which includes constructors for "not <", "not <=", "not >" and "not >=". Hence this type is closed under boolean negation, so to speak, and there is no longer a need for "Cnotcompf", given that "Ccompf" takes a fp_comparison and can therefore express all FP comparisons of interest.
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This commits adds code generation for the RISC-V architecture, both in 32- and 64-bit modes.
The generated code was lightly tested using the simulator and cross-binutils from https://riscv.org/software-tools/
This port required the following additional changes:
- Integers: More properties about shrx
- SelectOp: now provides smart constructors for mulhs and mulhu
- SelectDiv, 32-bit integer division and modulus: implement constant propagation, use the new smart constructors mulhs and mulhu.
- Runtime library: if no asm implementation is provided, run the reference C implementation through CompCert. Since CompCert rejects the definitions of names of special functions such as __i64_shl, the reference implementation now uses "i64_" names, e.g. "i64_shl", and a renaming "i64_ -> __i64_" is performed over the generated assembly file, before assembling and building the runtime library.
- test/: add SIMU make variable to run tests through a simulator
- test/regression/alignas.c: make sure _Alignas and _Alignof are not #define'd by C headers
commit da14495c01cf4f66a928c2feff5c53f09bde837f
Author: Xavier Leroy <xavier.leroy@inria.fr>
Date: Thu Apr 13 17:36:10 2017 +0200
RISC-V port, continued
Now working on Asmgen.
commit 36f36eb3a5abfbb8805960443d087b6a83e86005
Author: Xavier Leroy <xavier.leroy@inria.fr>
Date: Wed Apr 12 17:26:39 2017 +0200
RISC-V port, first steps
This port is based on Prashanth Mundkur's experimental RV32 port and brings it up to date with CompCert, and adds 64-bit support (RV64). Work in progress.
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