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Switch loops stack to use LoopBlocks.

Browse Source 
Also remove dead code.

Change-Id: I2c0177d8cab48b7d6f9442715aecb7951597f3c8
This commit is contained in:
Dejan Mircevski 2016-01-11 09:35:22 -05:00
parent 13228243b2
commit 7819bee82c
2 changed files with 16 additions and 213 deletions
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154
SPIRV/SpvBuilder.cpp
View File

@ -1761,155 +1761,31 @@ Block& Builder::makeNewBlock()
return *block;
}
Builder::LoopBlocks Builder::makeNewLoop()
Builder::LoopBlocks& Builder::makeNewLoop()
{
return {makeNewBlock(), makeNewBlock(), makeNewBlock()};
}
// Comments in header
void Builder::makeNewLoop(bool loopTestFirst)
{
loops.push(Loop(*this, loopTestFirst));
const Loop& loop = loops.top();
// The loop test is always emitted before the loop body.
// But if the loop test executes at the bottom of the loop, then
// execute the test only on the second and subsequent iterations.
// Remember the block that branches to the loop header. This
// is required for the test-after-body case.
Block* preheader = getBuildPoint();
// Branch into the loop
createBranch(loop.header);
// Set ourselves inside the loop
loop.function->addBlock(loop.header);
setBuildPoint(loop.header);
if (!loopTestFirst) {
// Generate code to defer the loop test until the second and
// subsequent iterations.
// It's always the first iteration when coming from the preheader.
// All other branches to this loop header will need to indicate "false",
// but we don't yet know where they will come from.
loop.isFirstIteration->addIdOperand(makeBoolConstant(true));
loop.isFirstIteration->addIdOperand(preheader->getId());
getBuildPoint()->addInstruction(loop.isFirstIteration);
// Mark the end of the structured loop. This must exist in the loop header block.
createLoopMerge(loop.merge, loop.header, LoopControlMaskNone);
// Generate code to see if this is the first iteration of the loop.
// It needs to be in its own block, since the loop merge and
// the selection merge instructions can't both be in the same
// (header) block.
Block* firstIterationCheck = new Block(getUniqueId(), *loop.function);
createBranch(firstIterationCheck);
loop.function->addBlock(firstIterationCheck);
setBuildPoint(firstIterationCheck);
// Control flow after this "if" normally reconverges at the loop body.
// However, the loop test has a "break branch" out of this selection
// construct because it can transfer control to the loop merge block.
createSelectionMerge(loop.body, SelectionControlMaskNone);
Block* loopTest = new Block(getUniqueId(), *loop.function);
createConditionalBranch(loop.isFirstIteration->getResultId(), loop.body, loopTest);
loop.function->addBlock(loopTest);
setBuildPoint(loopTest);
}
}
void Builder::createLoopTestBranch(Id condition)
{
const Loop& loop = loops.top();
// Generate the merge instruction. If the loop test executes before
// the body, then this is a loop merge. Otherwise the loop merge
// has already been generated and this is a conditional merge.
if (loop.testFirst) {
createLoopMerge(loop.merge, loop.header, LoopControlMaskNone);
// Branching to the "body" block will keep control inside
// the loop.
createConditionalBranch(condition, loop.body, loop.merge);
loop.function->addBlock(loop.body);
setBuildPoint(loop.body);
} else {
// The branch to the loop merge block is the allowed exception
// to the structured control flow. Otherwise, control flow will
// continue to loop.body block. Since that is already the target
// of a merge instruction, and a block can't be the target of more
// than one merge instruction, we need to make an intermediate block.
Block* stayInLoopBlock = new Block(getUniqueId(), *loop.function);
createSelectionMerge(stayInLoopBlock, SelectionControlMaskNone);
// This is the loop test.
createConditionalBranch(condition, stayInLoopBlock, loop.merge);
// The dummy block just branches to the real loop body.
loop.function->addBlock(stayInLoopBlock);
setBuildPoint(stayInLoopBlock);
createBranchToBody();
}
}
void Builder::createBranchToBody()
{
const Loop& loop = loops.top();
assert(loop.body);
// This is a reconvergence of control flow, so no merge instruction
// is required.
createBranch(loop.body);
loop.function->addBlock(loop.body);
setBuildPoint(loop.body);
loops.push({makeNewBlock(), makeNewBlock(), makeNewBlock()});
return loops.top();
}
void Builder::createLoopContinue()
{
createBranchToLoopHeaderFromInside(loops.top());
createBranch(&loops.top().continue_target);
// Set up a block for dead code.
createAndSetNoPredecessorBlock("post-loop-continue");
}
// Add an exit (e.g. "break") for the innermost loop that you're in
void Builder::createLoopExit()
{
createBranch(loops.top().merge);
createBranch(&loops.top().merge);
// Set up a block for dead code.
createAndSetNoPredecessorBlock("post-loop-break");
}
// Close the innermost loop
void Builder::closeLoop()
{
const Loop& loop = loops.top();
// Branch back to the top
createBranchToLoopHeaderFromInside(loop);
// Add the merge block and set the build point to it
loop.function->addBlock(loop.merge);
setBuildPoint(loop.merge);
loops.pop();
}
// Create a branch to the header of the given loop, from inside
// the loop body.
// Adjusts the phi node for the first-iteration value if needeed.
void Builder::createBranchToLoopHeaderFromInside(const Loop& loop)
{
createBranch(loop.header);
if (loop.isFirstIteration) {
loop.isFirstIteration->addIdOperand(makeBoolConstant(false));
loop.isFirstIteration->addIdOperand(getBuildPoint()->getId());
}
}
void Builder::clearAccessChain()
{
accessChain.base = NoResult;
@ -2273,24 +2149,4 @@ void MissingFunctionality(const char* fun)
exit(1);
}
Builder::Loop::Loop(Builder& builder, bool testFirstArg)
: function(&builder.getBuildPoint()->getParent()),
header(new Block(builder.getUniqueId(), *function)),
merge(new Block(builder.getUniqueId(), *function)),
body(new Block(builder.getUniqueId(), *function)),
testFirst(testFirstArg),
isFirstIteration(nullptr)
{
if (!testFirst)
{
// You may be tempted to rewrite this as
// new Instruction(builder.getUniqueId(), builder.makeBoolType(), OpPhi);
// This will cause subtle test failures because builder.getUniqueId(),
// and builder.makeBoolType() can then get run in a compiler-specific
// order making tests fail for certain configurations.
Id instructionId = builder.getUniqueId();
isFirstIteration = new Instruction(instructionId, builder.makeBoolType(), OpPhi);
}
}
}; // end spv namespace

75
SPIRV/SpvBuilder.h
View File

@ -373,35 +373,24 @@ public:
// Finish off the innermost switch.
void endSwitch(std::vector<Block*>& segmentBB);
// Start the beginning of a new loop, and prepare the builder to
// generate code for the loop test.
// The loopTestFirst parameter is true when the loop test executes before
// the body. (It is false for do-while loops.)
void makeNewLoop(bool loopTestFirst);
struct LoopBlocks {
Block &body, &merge, &continue_target;
};
LoopBlocks makeNewLoop();
// Create a new block in the function containing the build point.
// Start a new loop and prepare the builder to generate code for it. Until
// closeLoop() is called for this loop, createLoopContinue() and
// createLoopExit() will target its corresponding blocks.
LoopBlocks& makeNewLoop();
// Create a new block in the function containing the build point. Memory is
// owned by the function object.
Block& makeNewBlock();
// Add the branch for the loop test, based on the given condition.
// The true branch goes to the first block in the loop body, and
// the false branch goes to the loop's merge block. The builder insertion
// point will be placed at the start of the body.
void createLoopTestBranch(Id condition);
// Generate an unconditional branch to the loop body. The builder insertion
// point will be placed at the start of the body. Use this when there is
// no loop test.
void createBranchToBody();
// Add a branch to the test of the current (innermost) loop.
// The way we generate code, that's also the loop header.
// Add a branch to the continue_target of the current (innermost) loop.
void createLoopContinue();
// Add an exit (e.g. "break") for the innermost loop that you're in
// Add an exit (e.g. "break") from the innermost loop that we're currently
// in.
void createLoopExit();
// Close the innermost loop that you're in
@ -517,9 +506,6 @@ public:
void createSelectionMerge(Block* mergeBlock, unsigned int control);
void dumpInstructions(std::vector<unsigned int>&, const std::vector<Instruction*>&) const;
struct Loop; // Defined below.
void createBranchToLoopHeaderFromInside(const Loop& loop);
SourceLanguage source;
int sourceVersion;
std::vector<const char*> extensions;
@ -550,47 +536,8 @@ public:
// stack of switches
std::stack<Block*> switchMerges;
// Data that needs to be kept in order to properly handle loops.
struct Loop {
// Constructs a default Loop structure containing new header, merge, and
// body blocks for the current function.
// The testFirst argument indicates whether the loop test executes at
// the top of the loop rather than at the bottom. In the latter case,
// also create a phi instruction whose value indicates whether we're on
// the first iteration of the loop. The phi instruction is initialized
// with no values or predecessor operands.
Loop(Builder& builder, bool testFirst);
// The function containing the loop.
Function* const function;
// The header is the first block generated for the loop.
// It dominates all the blocks in the loop, i.e. it is always
// executed before any others.
// If the loop test is executed before the body (as in "while" and
// "for" loops), then the header begins with the test code.
// Otherwise, the loop is a "do-while" loop and the header contains the
// start of the body of the loop (if the body exists).
Block* const header;
// The merge block marks the end of the loop. Control is transferred
// to the merge block when either the loop test fails, or when a
// nested "break" is encountered.
Block* const merge;
// The body block is the first basic block in the body of the loop, i.e.
// the code that is to be repeatedly executed, aside from loop control.
// This member is null until we generate code that references the loop
// body block.
Block* const body;
// True when the loop test executes before the body.
const bool testFirst;
// When the test executes after the body, this is defined as the phi
// instruction that tells us whether we are on the first iteration of
// the loop. Otherwise this is null. This is non-const because
// it has to be initialized outside of the initializer-list.
Instruction* isFirstIteration;
};
// Our loop stack.
std::stack<Loop> loops;
std::stack<LoopBlocks> loops;
}; // end Builder class
// Use for non-fatal notes about what's not complete