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      contributors may be used to endorse or promote products derived from
      this software without specific prior written permission.


   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
   IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
   TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
   PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER
   OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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*/

#include "IsCompileTimeConstant.h"

namespace ispc {

char IsCompileTimeConstantPass::ID = 0;

bool IsCompileTimeConstantPass::lowerCompileTimeConstant(llvm::BasicBlock &bb) {
    DEBUG_START_BB("IsCompileTimeConstantPass");

    llvm::Function *funcs[] = {m->module->getFunction("__is_compile_time_constant_mask"),
                               m->module->getFunction("__is_compile_time_constant_uniform_int32"),
                               m->module->getFunction("__is_compile_time_constant_varying_int32")};

    bool modifiedAny = false;
restart:
    for (llvm::BasicBlock::iterator i = bb.begin(), e = bb.end(); i != e; ++i) {
        // Iterate through the instructions looking for calls to the
        // __is_compile_time_constant_*() functions
        llvm::CallInst *callInst = llvm::dyn_cast<llvm::CallInst>(&*i);
        if (callInst == NULL)
            continue;

        int j;
        int nFuncs = sizeof(funcs) / sizeof(funcs[0]);
        for (j = 0; j < nFuncs; ++j) {
            if (funcs[j] != NULL && callInst->getCalledFunction() == funcs[j])
                break;
        }
        if (j == nFuncs)
            // not a __is_compile_time_constant_* function
            continue;

        // This optimization pass can be disabled with both the (poorly
        // named) disableGatherScatterFlattening option and
        // disableMaskAllOnOptimizations.
        if (g->opt.disableGatherScatterFlattening || g->opt.disableMaskAllOnOptimizations) {
            ReplaceInstWithValueWrapper(i, LLVMFalse);
            modifiedAny = true;
            goto restart;
        }

        // Is it a constant?  Bingo, turn the call's value into a constant
        // true value.
        llvm::Value *operand = callInst->getArgOperand(0);
        if (llvm::isa<llvm::Constant>(operand)) {
            ReplaceInstWithValueWrapper(i, LLVMTrue);
            modifiedAny = true;
            goto restart;
        }

        // This pass runs multiple times during optimization.  Up until the
        // very last time, it only replaces the call with a 'true' if the
        // value is known to be constant and otherwise leaves the call
        // alone, in case further optimization passes can help resolve its
        // value.  The last time through, it eventually has to give up, and
        // replaces any remaining ones with 'false' constants.
        if (isLastTry) {
            ReplaceInstWithValueWrapper(i, LLVMFalse);
            modifiedAny = true;
            goto restart;
        }
    }

    DEBUG_END_BB("IsCompileTimeConstantPass");

    return modifiedAny;
}

bool IsCompileTimeConstantPass::runOnFunction(llvm::Function &F) {

    llvm::TimeTraceScope FuncScope("IsCompileTimeConstantPass::runOnFunction", F.getName());
    bool modifiedAny = false;
    for (llvm::BasicBlock &BB : F) {
        modifiedAny |= lowerCompileTimeConstant(BB);
    }
    return modifiedAny;
}

llvm::Pass *CreateIsCompileTimeConstantPass(bool isLastTry) { return new IsCompileTimeConstantPass(isLastTry); }

} // namespace ispc