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Add custom basic dead instruction elimination pass

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This commit is contained in:
gingerBill
2021-05-15 21:10:06 +01:00
parent 7886798156
commit 1cf6b6679d
2 changed files with 108 additions and 13 deletions
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93
src/llvm_backend_opt.cpp
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@@ -248,3 +248,96 @@ void lb_populate_module_pass_manager(LLVMTargetMachineRef target_machine, LLVMPa
LLVMAddCFGSimplificationPass(mpm);
}
void lb_run_remove_dead_instruction_pass(lbProcedure *p) {
isize removal_count = 0;
isize pass_count = 0;
isize const max_pass_count = 10;
// Custom remove dead instruction pass
for (; pass_count < max_pass_count; pass_count++) {
bool was_dead_instructions = false;
// NOTE(bill): Iterate backwards
// reduces the number of passes as things later on will depend on things previously
for (LLVMBasicBlockRef block = LLVMGetLastBasicBlock(p->value);
block != nullptr;
block = LLVMGetPreviousBasicBlock(block)) {
// NOTE(bill): Iterate backwards
// reduces the number of passes as things later on will depend on things previously
for (LLVMValueRef instr = LLVMGetLastInstruction(block);
instr != nullptr;
/**/) {
LLVMValueRef curr_instr = instr;
instr = LLVMGetPreviousInstruction(instr);
LLVMUseRef first_use = LLVMGetFirstUse(curr_instr);
if (first_use != nullptr) {
continue;
}
if (LLVMTypeOf(curr_instr) == nullptr) {
continue;
}
// NOTE(bill): Explicit instructions are set here because some instructions could have side effects
switch (LLVMGetInstructionOpcode(curr_instr)) {
case LLVMAdd:
case LLVMFAdd:
case LLVMSub:
case LLVMFSub:
case LLVMMul:
case LLVMFMul:
case LLVMUDiv:
case LLVMSDiv:
case LLVMFDiv:
case LLVMURem:
case LLVMSRem:
case LLVMFRem:
case LLVMShl:
case LLVMLShr:
case LLVMAShr:
case LLVMAnd:
case LLVMOr:
case LLVMXor:
case LLVMAlloca:
case LLVMLoad:
case LLVMGetElementPtr:
case LLVMTrunc:
case LLVMZExt:
case LLVMSExt:
case LLVMFPToUI:
case LLVMFPToSI:
case LLVMUIToFP:
case LLVMSIToFP:
case LLVMFPTrunc:
case LLVMFPExt:
case LLVMPtrToInt:
case LLVMIntToPtr:
case LLVMBitCast:
case LLVMAddrSpaceCast:
case LLVMICmp:
case LLVMFCmp:
case LLVMSelect:
case LLVMExtractElement:
removal_count += 1;
LLVMInstructionEraseFromParent(curr_instr);
was_dead_instructions = true;
break;
}
}
}
if (!was_dead_instructions) {
break;
}
}
}
void lb_run_function_pass_manager(LLVMPassManagerRef fpm, lbProcedure *p) {
LLVMRunFunctionPassManager(fpm, p->value);
// NOTE(bill): LLVMAddDCEPass doesn't seem to be exported in the official DLL's for LLVM
// which means we cannot rely upon it
// This is also useful for read the .ll for debug purposes because a lot of instructions
// are not removed
lb_run_remove_dead_instruction_pass(p);
}