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Add option to turn off codegen improvements when mask 'all on' is statically known.

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This commit is contained in:
Matt Pharr
2011-12-11 16:16:36 -08:00
parent 20536bb339
commit 46bfef3fce
7 changed files with 88 additions and 33 deletions
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49
ctx.cpp
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@@ -197,6 +197,47 @@ FunctionEmitContext::FunctionEmitContext(Function *func, Symbol *funSym,
returnValuePtr = AllocaInst(ftype, "return_value_memory");
}
if (g->opt.disableMaskAllOnOptimizations) {
// This is really disgusting. We want to be able to fool the
// compiler to not be able to reason that the mask is all on, but
// we don't want to pay too much of a price at the start of each
// function to do so.
//
// Therefore: first, we declare a module-static __all_on_mask
// variable that will hold an "all on" mask value. At the start of
// each function, we'll load its value and call SetInternalMaskAnd
// with the result to set the current internal execution mask.
// (This is a no-op at runtime.)
//
// Then, to fool the optimizer that maybe the value of
// __all_on_mask can't be guaranteed to be "all on", we emit a
// dummy function that sets __all_on_mask be "all off". (That
// function is never actually called.)
llvm::Value *globalAllOnMaskPtr =
m->module->getNamedGlobal("__all_on_mask");
if (globalAllOnMaskPtr == NULL) {
globalAllOnMaskPtr =
new llvm::GlobalVariable(*m->module, LLVMTypes::MaskType, false,
llvm::GlobalValue::InternalLinkage,
LLVMMaskAllOn, "__all_on_mask");
char buf[256];
sprintf(buf, "__off_all_on_mask_%s", g->target.GetISAString());
llvm::Constant *offFunc =
m->module->getOrInsertFunction(buf, LLVMTypes::VoidType,
NULL);
assert(llvm::isa<llvm::Function>(offFunc));
llvm::BasicBlock *offBB =
llvm::BasicBlock::Create(*g->ctx, "entry",
(llvm::Function *)offFunc, 0);
new llvm::StoreInst(LLVMMaskAllOff, globalAllOnMaskPtr, offBB);
llvm::ReturnInst::Create(*g->ctx, offBB);
}
llvm::Value *allOnMask = LoadInst(globalAllOnMaskPtr, "all_on_mask");
SetInternalMaskAnd(LLVMMaskAllOn, allOnMask);
}
if (m->diBuilder) {
/* If debugging is enabled, tell the debug information emission
code about this new function */
@@ -271,7 +312,8 @@ FunctionEmitContext::GetFunctionMask() {
llvm::Value *
FunctionEmitContext::GetInternalMask() {
if (VaryingCFDepth() == 0)
if (VaryingCFDepth() == 0 &&
!g->opt.disableMaskAllOnOptimizations)
return LLVMMaskAllOn;
else
return LoadInst(internalMaskPointer, "load_mask");
@@ -281,7 +323,8 @@ FunctionEmitContext::GetInternalMask() {
llvm::Value *
FunctionEmitContext::GetFullMask() {
llvm::Value *internalMask = GetInternalMask();
if (internalMask == LLVMMaskAllOn && functionMaskValue == LLVMMaskAllOn)
if (internalMask == LLVMMaskAllOn && functionMaskValue == LLVMMaskAllOn &&
!g->opt.disableMaskAllOnOptimizations)
return LLVMMaskAllOn;
else
return BinaryOperator(llvm::Instruction::And, GetInternalMask(),
@@ -2047,7 +2090,7 @@ FunctionEmitContext::StoreInst(llvm::Value *value, llvm::Value *ptr,
if (ptrType->GetBaseType()->IsUniformType())
// the easy case
StoreInst(value, ptr);
else if (mask == LLVMMaskAllOn)
else if (mask == LLVMMaskAllOn && !g->opt.disableMaskAllOnOptimizations)
// Otherwise it is a masked store unless we can determine that the
// mask is all on... (Unclear if this check is actually useful.)
StoreInst(value, ptr);