similar to: [LLVMdev] PHI nodes in machine code

On Thu, Jul 08, 2004 at 08:06:29PM +0400, Vladimir Prus wrote: > Could anybody quickly explain why PHI nodes instructions are necessary > in machine code? And why the code in LiveVariables.cpp which looks at > those PHI nodes (line 249 and below) is necessary. LLVM Machine code is in SSA. Let's say you want to do r = a cond b But doing this: if (a cond b) then r = 1

PHI nodes within machine code were originally used by the Sparc back-end but they turned out not to be necessary. Instead, LLVM phis are lowered to copy instructions in the machine code (I believe this happens just after instruction selection). As far as I know, the machine PHI nodes are not used by the x86 back-end and you shouldn't need them if you insert the right copies. --Vikram

Misha Brukman wrote: > LLVM Machine code is in SSA. This explains quite a lot. I though it's possible to just reduce convert phis into copy instructions in predecessors -- all of which will have the same destination register. > gets you two definitions of r. So we have machine PHI nodes merge the > two possible values into one for result of r. These phis get removed > after

Hi, I'm lowering some of the logical operators (by example the | operator) on integer32. Sadly my target only provide native instruction on high and low parts of 32 bits registers. So, I have to generate a sequence of two native instructions (LOR followed by HOR). I've introduced an Pseudo instruction with a custom inserter. def OR_A_oo : CLPPseudoInst<(ins

hello... I am trying to get this code to work, but as I get to the predict command, it displays an error due to the length of the data sets from the removal of the NA's. Here is the data, and the code that I am using so far, if you run it, you'll see the error pop up.... please help me to get around this problem. Thanks in advance. Location Dist. Size low1 .5 10.5 low2 .5 23 low3 .5 NA

Hi everybody hacking in the 200-pre4 i found everything i needed, so i gave it a try ... and it works! But dont blame for the code, its just quick and dirty! --- ../syslinux-2.00-pre4/pxelinux.asm Sat Jun 15 07:25:51 2002 +++ ./pxelinux.asm Wed Aug 14 10:05:00 2002 @@ -17,6 +17,11 @@ ; version; incorporated herein by reference. ; ;

Let's say I have the following IR code: 21> %tmp = load i32* @myrand.z, align 4 22> %tmp1 = and i32 %tmp, 5535 23> %tmp2 = mul nsw i32 %tmp1, 36969 24> %tmp3 = ashr i32 %tmp, 16 And I have an Instruction *inst that is the instruction on line 22. then have the code: Use *operand1 = &(inst->getOperandUse(0)); I expect that operand1->getNext() will return the the Use*

I've read that LiveValues has been removed from trunk. Did it bitrot or was simply removed because a replacement is available? If it's the former, what caused the bitrotting? If it's the latter, what's the replacement? (I've found LiveVariables but I'm not sure it can be used in a ModulePass). b.r. -- Carlo Alberto Ferraris <cafxx at strayorange.com <mailto:cafxx

Hi, Clang normally generates code that looks like .... ; <label>:22 ; preds = %0 %23 = call i32 (i8*, ...)* @printf(i8* getelementptr inbounds ([24 x i8]* @.str, i32 0, i32 0)) br label %24 ; <label>:24 ; preds = %22, %0 %25 = load i32* %tmphigh, align 4 %26 = and i32 %25, 65535 store i32 %26, i32*

LiveVariables is the optimized and tested way to get variable liveness information (it's used by register allocation). Unfortunately it requires a MachineFunction to work - so you'll either need to lower to one of the built-in targets or add your own target to acquire access to this pass. Andrew On 03/31/2011 12:28 PM, Carlo Alberto Ferraris wrote: > I've read that LiveValues

Hi Chris, > Clang normally generates code that looks like > > .... > ;<label>:22 ; preds = %0 > %23 = call i32 (i8*, ...)* @printf(i8* getelementptr inbounds ([24 x i8]* > @.str, i32 0, i32 0)) > br label %24 > > ;<label>:24 ; preds = %22, %0 > %25 = load i32* %tmphigh,

How does the verifier deal with this? I'm noticing that if I load a clang compiled function (with -emit-llvm) and run the verifier, there is no problem. If I start mucking with the function body (adding an instruction), the verifier is unhappy saying the instructions that would have been in the commented out block aren't part of a basic block. Does the clang compiled function have some

So if I first create the value in an entry BB and then build a CopyToReg but then I have to read it in a BB that loops back to itself, with it's own CopyToReg at the end, then I have two CopyToReg nodes for the same value. In this case, I need to create 3 virt regs, 1 for each CopyToReg and a third for the CopyFromReg in the beginning of the loop BB, right? And then I need to build a PHI

On Feb 8, 2013, at 4:03 PM, Cameron Zwarich <zwarich at apple.com> wrote: > How much of the work is done here? I'd be happy to do the phi elimination part, since I basically did that for StrongPhiElimination (RIP). Any help would be appreciated. I did a bit of the easy stuff in 2-addr, it has a LIS = getAnalysisIfAvailable<LiveIntervals>() member that it sometimes updates. It

Rotem Varon wrote: > Hi, > > Let say i am writing a code inside basic block pass and iterating all > the instructions inside, > and i encountered in this instruction : If you're asking how to get the operands of an Instruction, use the getOperand() method: Value * Operand1 = I->getOperand(0); Value * Operand2 = I->getOperand(1); The LLVM doxygen documentation

On Feb 8, 2013, at 4:20 PM, Jakob Stoklund Olesen <stoklund at 2pi.dk> wrote: > On Feb 8, 2013, at 4:03 PM, Cameron Zwarich <zwarich at apple.com> wrote: > >> How much of the work is done here? I'd be happy to do the phi elimination part, since I basically did that for StrongPhiElimination (RIP). > > Any help would be appreciated. > > I did a bit of the

SimplifyCFG FoldTwoEntryPhiNode looks to simplify all 2 entry phi nodes in a block, if it can't do them all then it won't do any and returns. There is a lot of code that is directly in this function geared toward this requirement. Is it possible currently to get this function (or pass) to simply fold "some" of the phis (without having to fold them all?). I understand that

On 30.8.2011, at 19.19, Eli Friedman wrote: > reg2mem won't do quite this transformation... not sure exactly what you need. I need to get rid of phis. This code is compiled from C++ and for some functions there are no phis, but multiple call instructions. I am targeting hardware in the end, and the next tool reading the IR does not like phis when it's generating VHDL. My questions may

Conditional on the target supporting cmov? Though that's probably not optimal. On Wed, Feb 5, 2020, 7:47 AM Nicolai Hähnle <nhaehnle at gmail.com> wrote: > Hi Ryan, > > On Mon, Feb 3, 2020 at 7:08 PM Ryan Taylor via llvm-dev > <llvm-dev at lists.llvm.org> wrote: > > SimplifyCFG FoldTwoEntryPhiNode looks to simplify all 2 entry phi nodes > in a block, if it

I am splitting a one BB loop into two BB. Basically, the one loop BB has 3 incoming values, one form back edge two from other edges. I want to extract the PHIs from the other two edges out into it's own BB and delete that from the loop, then redirect the backedge to the loopbody (non extracted portion) and create a new PHI coming from the extracted BB and the backedge. I can do this;