kbuild: Add support for Clang's polyhedral loop optimizer (Polly).

Signed-off-by: Diab Neiroukh <[email protected]>

Author: lzlrd

Makefile

@@ -722,6 +722,14 @@ KBUILD_CFLAGS	+= $(call cc-disable-warning,maybe-uninitialized,)
 endif
 endif
 
+ifdef CONFIG_POLLY_CLANG
+KBUILD_CFLAGS	+= -mllvm -polly \
+		   -mllvm -polly-vectorizer=stripmine
+ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION
+KBUILD_CFLAGS	+= -mllvm -polly-run-dce
+endif
+endif
+
 KBUILD_CFLAGS += $(call cc-ifversion, -lt, 0409, \
 			$(call cc-disable-warning,maybe-uninitialized,))
 

arch/Kconfig

@@ -587,6 +587,18 @@ config SHADOW_CALL_STACK_VMAP
 	  provides better stack exhaustion protection, but increases per-thread
 	  memory consumption as a full page is allocated for each shadow stack.
 
+config POLLY_CLANG
+        bool "Use clang Polly optimizations"
+        depends on CC_HAS_POLLY
+        help
+	  This option enables Clang's polyhedral loop optimizer known as Polly.
+	  Polly is able to optimize various loops throughout the kernel for
+	  cache locality. This requires a Clang toolchain compiled with
+	  support for Polly. More information can be found from Polly's
+	  website:
+
+	    https://polly.llvm.org
+
 config HAVE_ARCH_WITHIN_STACK_FRAMES
 	bool
 	help

init/Kconfig

@@ -29,6 +29,10 @@ config CLANG_VERSION
 config CC_HAS_ASM_GOTO
 	def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))
 
+config CC_HAS_POLLY
+	depends on CC_IS_CLANG
+	def_bool $(success,$(srctree)/scripts/clang-polly.sh $(CC))
+
 config TOOLS_SUPPORT_RELR
 	def_bool $(success,env "CC=$(CC)" "LD=$(LD)" "NM=$(NM)" "OBJCOPY=$(OBJCOPY)" $(srctree)/scripts/tools-support-relr.sh)
 

scripts/clang-polly.sh

@@ -0,0 +1,12 @@
+#! /bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2021, Diab Neiroukh <[email protected]>
+
+# Get the LLVM library directory from the configuration tool.
+pollyLib="$($(dirname $(which $@))/llvm-config --libdir)/LLVMPolly.so"
+
+if [ -f "$pollyLib" ]; then
+	exit 0
+else
+	exit 1
+fi