Bdtyktl

Programming language development has been influenced by hardware design. One example from this answer mentions how C pointers were, at least in part, influenced by the design of the PDP-11. Has the reverse taken place, where a construct provided by a language drove the development of hardware?

To be clear, I'm wondering about core language constructs, like pointers for example, rather than industry consortiums coming up with something like OpenGL then being implemented in hardware. Perhaps hardware floating-point support?

Simply yes.

And not just a few instructions, but whole CPUs have been developed with languages in mind. Most prominent maybe Intel's 8086. Already the basic CPU was designed to support the way high level languages handle memory management, especially stack allocation and usage. With BP a separate register for stack frames and addressing was added in conjunction with short encodings for stack related addressing to make HLL programs perform. The 80186/286 went further in this direction by adding Enter/Leave instructions for stack frame handling.

While it can be said that the base 8086 was more geared toward languages like Pascal or PL/M (*1,2), later incarnations added many ways to support the now prevalent C primitives - not at least scaling factors for indices.

*1 - Most remarkable here the string functions which make only sense in languages supporting strings as discrete data type.

*2 - Stephen Morse's 8086 primer is still a good read - especially when he talks about the finer details. Similar and quite recommended his 2008 interview about the 8086 creation where he describes his approach as mostly HLL driven.

Yes. Case in point, the VAX. The instruction set design was influenced by the requirements of the compiled languages of the day. For example, the orthogonality of the ISA; the provision of instructions that map to language constructs such as 'case' statements (in the numbered-case sense of Hoare's original formulation, not the labelled-case of C), loop statements, and so on.

VAX Architecture Ref - see the Introduction.

I am not claiming the VAX is unique in this respect, just an example I know a little about. As a second example, I'll mention the Burroughs B6500 'display' registers. A display, in 1960s speak, is a mechanism for efficient uplevel references. If your language, such as Algol60, permits declaration of nested procedures to any depth, then arbitrary references to the local variables of different levels of enclosing procedure require special handling. The mechanism used (the 'display') was invented for KDF9 Whetstone Algol by Randell and Russell, and described in their book Algol 60 Implementation. The B6500 incorporates that into hardware:

The B6500/B7500 contains a network of Display Registers (D0 through
D31) which are caused to point at the appropriate MSCW (Fig. 5). The
local variables of all procedures global to the current procedure are
addressed in the B6500/B7500 relative to the Display Registers.

I recall, back in the 80’s, and referenced in the Wikipedia article, Bellmac 32 CPU, which became the AT&T Western Electric WE32100 CPU was supposedly designed for the C programming language.

This CPU was used by AT&T in their 3B2 line of Unix systems. There was also a single board VME bus version of it that some third parties used. Zilog also came out with a line of Unix systems using this chip - I think they were a second source for it for AT&T.

I did a lot of work with these in the 80’s and probably early 90’s. It was pretty much a dog in terms of performance, if I remember.

Arguably, the relatively simple logical structure of DO loops in Fortran motivated the development of vector hardware on the early Cray and Cyber supercomputers. There may be some "chicken and egg" between hardware and software development though, since CDC Fortran included array slicing operations to encourage programmers to write "logic-free" loops long before that syntax became standardized in Fortran 90.

Certainly the Cray XMP hardware enhancements compared with the Cray 1, such as improved "chaining" (i.e. overlapping in time) of vector operations, vector mask instructions, and gather/scatter vector addressing, were aimed at improving the performance of typical code written in "idiomatic" Fortran.

The need to find a way to overcome the I/O bottlenecks caused by faster computation, without the prohibitive expense of large fast memory, led to the development of the early Cray SSD storage devices as an intermediate level between main memory conventional disk and tape storage devices. Fortran I/O statements made it easy to read and write a random-access file as if it were a large two-dimensional array of data.

See section 2 of http://www.chilton-computing.org.uk/ccd/supercomputers/p005.htm for an 1988 paper by the head of the Cray XMP design team.

There was a downside to this, in that the performance of the first Cray C compilers (and hence the first implementation of the Unix-like Cray operating system UNICOS) was abysmal, since the hardware had no native character-at-a-time instructions, and there was little computer science theory available to attempt to vectorize idiomatic "C-style" loops with a relatively unstructured combination of pointer manipulation and logical tests, compared with Fortran's more rigidly structured DO loops.

The first page of the Intel 8086 data sheet lists the processor's features, which include

• Architecture Designed for Powerful Assembly Language and Efficient High Level Languages

In particular, C and other high-level languages use the stack for arguments and local variables. The 8086 has both a stack pointer (SP) and a frame pointer (BP) which address memory using the stack segment (SS) rather than other segments (CS, DS, ES).

The datasheet for the 8087 co-processor has the following section:

PROGRAMMING LANGUAGE SUPPORT

Programs for the 8087 can be written in Intel's high-level languages for 8086/8088 and 80186/80188 systems; ASM-86 (the 8086, 8088 assembly language), PL/M-86, FORTRAN-86, and PASCAL-86.

The 80286 added several instructions to the architecture to aid high-level languages. PUSHA, POPA, ENTER, and LEAVE help with subroutine calls. The BOUND instruction was useful for array bounds checking and switch-style control statements. Other instructions unrelated to high-level languages were added as well.

The 80386 added bitfield instructions, which are used in C.

The Motorola MC68000 Microprocessor User's Manual states:

2.2.2 Structured Modular Programming

[...]
The availability of advanced, structured assemblers and block-structured high-level languages such as Pascal simplifies modular programming. Such concepts are virtually useless, however, unless parameters are easily transferred between and within software modules that operate on a re-entrant and recursive basis.
[...]
The MC68000 provides architectural features that allow efficient re-entrant modular programming. Two complementary instructions, link and allocate (LINK) and unlink (UNLK), reduce subroutine call overhead by manipulating linked lists of data areas on the stack. The move multiple register instruction (MOVEM) also reduces subroutine call programming overhead.
[...]
Other instructions that support modern structured programming techniques are push effective address (PEA), load effective address (LEA), return and restore (RTR), return from exception (RTE), jump to subroutine (JSR), branch to subroutine (BSR), and return from subroutine (RTS).

The 68020 added bitfield instructions, which are used in C.

Whereas the above processors added instructions to support programming languages, Reduced Instruction-Set Computers (RISC) took the opposite approach. By analyzing which instructions compilers actually used, they were able to discard many complex instructions that weren't being used. This allowed the architecture to be simplified, shorten the instruction cycle length, and reduce instructions to one cycle, speeding up processors significantly.