MIPS32 processors have "delayed" loads and MIPS32 manual says that the instruction immediately following a branch is always executed, regardless of whether the branch is taken or compilers try to fill a branch delay slot with an appropriate instruction. The MIPS R4000, part 9: Stupid branch delay slot tricks In the branch delay slot, we edit the return address so that when function1 returns, it resumes execution at resume rather than nominal_return, thereby avoiding having to executeThe MIPS R4000 had a four-stage pipeline, and a branch misprediction would consequently suffer a 2-cycle stall. Does mips branch delay slots propagates through... -…
RISC Microprocessors Examples: MIPS & ARM
My guess would be to move the lw instruction after the branch instruction since (as far as I understand) the instruction in the delay slot is always executed. Then again, I don't quite understand this subject and I would appreciate an explination. I understand pipelining in general, but not so much delayed branching. Thanks MIPS architecture - Wikipedia All MIPS I control flow instructions are followed by a branch delay slot. Unless the branch delay slot is filled by an instruction performing useful work, an nop is substituted. MIPS I branch instructions compare the contents of a GPR (rs) against zero or another GPR (rt) as signed integers and branch if the specified condition is true. assembly - MIPS (PIC32): branch vs. branch likely ... So in the R4000 architecture, MIPS added Branch Likely instructions which still always fetch the instruction after the branch from the instruction cache, but only execute it if the branch is taken (opposite of what one might expect). Compilers can then always fill the branch delay slot on such a branch. A loop like:
CMSC 411 Computer Systems Architecture Lecture 5 Basic ...
As a disclaimer, I've never worked with a real MIPS machine, but I imagine that using a branch delay slot for another branch will almost certainly cause problems. One common practice on processors like MIPS is to use the branch delay slot for a no-op, such as ori $0, $0, 0, just to make sure that nothing executes that isn't supposed to. Classic RISC pipeline - Wikipedia The SPARC, MIPS, and MC88K designers designed a branch delay slot into their ISAs. Branch Prediction: In parallel with fetching each instruction, guess if the instruction is a branch or jump, and if so, guess the target. On the cycle after a branch or jump, fetch the instruction at the guessed target. assembly - Delayed Branching in MIPS - Stack Overflow My guess would be to move the lw instruction after the branch instruction since (as far as I understand) the instruction in the delay slot is always executed. Then again, I don't quite understand this subject and I would appreciate an explination. I understand pipelining in general, but not so much delayed branching. Thanks MIPS architecture - Wikipedia
The SHARC DSP and MIPS-X use a double branch delay ... The ideal number of branch delay slots in a particular pipeline ...
This would cause a bubble in the pipeline; therefore some RISC architectures have a branch delay slot: The instruction after the branch will always be executed, no matter whether the branch is taken or not.
How a Jump Works
Pipelining: Branch Hazards CSE 141, S2'06 Jeff Brown Eliminating the Branch Stall • There’s no rule that says we have to see the effect of the branch immediately. Why not wait an extra instruction before branching? • The original SPARC and MIPS processors each used a single branch delay slot to … Having Fun with Branch Delay Slots – pagetable.com Abusing the load delay or branch delay on MIPS-I (and probably later chips too) is only safe if there is no way an interrupt can occur. When an interrupt occurs in a branch delay slot, the cpu subtracts 4 from the PC. However if you have a branch in a branch delay slot, then the CPU will subtract 4 from the address the second branch pointed at. MIPS architecture - Wikipedia All MIPS I control flow instructions are followed by a branch delay slot. Unless the branch delay slot is filled by an instruction performing useful work, an nop is substituted. MIPS I branch instructions compare the contents of a GPR (rs) against zero or another GPR (rt) as signed integers and branch … Classic RISC pipeline - Wikipedia
MIPS Processor Implementation