Antonio Frighetto antoniofrighetto

EarlyCSE performs unwanted optimization – Analysis

Recall that precall_hook and postcall_hook markers surround IR instructions containing calls to opaque functions (registers_clobbered) which are used to say which register variables were clobbered by the original callee. All calls have attribute readonly and nounwind. opaque_true function call is used to prevent DCE (we make all branch conditions opaque).

Before EarlyCSE

In the process of testing tac coreutil binary, for a specific functions we have the following BBs (only relevant parts are included):

; *** IR Dump After Simplify the CFG ***

	// If possible, canonicalize GE/LE comparisons to GT/LT comparisons, by
	// adding or subtracting 1 from one of the operands.
	enum class OperandKind { LHS, RHS };

	struct Rule {
	struct OpStep {
	uint64_t Adjustment;
	SCEV::NoWrapFlags Flags;
	};

	// 2k20 antoniofrighetto & benjamin

	#include <assert.h>
	#include <stdio.h>
	#include <stdlib.h>
	#include <stdint.h>
	#include <string.h>
	#include <unistd.h>
	#include <pthread.h>
	#include <mach/mach.h>

	# !/bin/bash
	# 2k20 ~antoniofrighetto
	# Build any XNU kernel version. Make sure you have the related MacOSX SDK version installed
	#
	# macOS 10.15.4 kernel compilation successfully tested on macOS 10.15.6 and Xcode 11.6
	#
	# MACOS_VERSION=10.15.4 BACKUP_SDK=1 OPTIONS=RELEASE,DEVELOPMENT ./build-xnu.sh
	# XNU_VERSION=xnu-4570.41.2 ./build-xnu.sh

	set_macos_version() {