Makefile: Rework on Polly optimizer flags

Commits that have been squashed are as follows:

1. d569f7e09f
2. 24a11f1008
3. 50e16d01b4
4. 86fb97a73b

[ Tashar02: Conditionally place the flags as they are only supported by clang greater than version 13.0.0 ]

Signed-off-by: Dakkshesh <dakkshesh5@gmail.com>
Co-authored-by: Tashfin Shakeer Rhythm <tashfinshakeerrhythm@gmail.com>
Signed-off-by: Tashfin Shakeer Rhythm <tashfinshakeerrhythm@gmail.com>
Signed-off-by: Divyanshu-Modi <divyan.m05@gmail.com>
Signed-off-by: Adithya R <gh0strider.2k18.reborn@gmail.com>

Makefile

@@ -811,11 +811,30 @@ endif
 ifdef CONFIG_LLVM_POLLY
 KBUILD_CFLAGS	+= -mllvm -polly \
 		   -mllvm -polly-run-inliner \
-		   -mllvm -polly-opt-fusion=max \
 		   -mllvm -polly-ast-use-context \
 		   -mllvm -polly-detect-keep-going \
-		   -mllvm -polly-vectorizer=stripmine \
-		   -mllvm -polly-invariant-load-hoisting
+		   -mllvm -polly-invariant-load-hoisting \
+		   -mllvm -polly-vectorizer=stripmine
+
+ifeq ($(shell test $(CONFIG_CLANG_VERSION) -gt 130000; echo $$?),0)
+KBUILD_CFLAGS	+= -mllvm -polly-loopfusion-greedy=1 \
+		   -mllvm -polly-reschedule=1 \
+		   -mllvm -polly-postopts=1 \
+		   -mllvm -polly-num-threads=0 \
+		   -mllvm -polly-omp-backend=LLVM \
+		   -mllvm -polly-scheduling=dynamic \
+		   -mllvm -polly-scheduling-chunksize=1
+else
+KBUILD_CFLAGS	+= -mllvm -polly-opt-fusion=max
+endif
+
+# Polly may optimise loops with dead paths beyound what the linker
+# can understand. This may negate the effect of the linker's DCE
+# so we tell Polly to perfom proven DCE on the loops it optimises
+# in order to preserve the overall effect of the linker's DCE.
+ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION
+POLLY_FLAGS	+= -mllvm -polly-run-dce
+endif
 endif
 
 # Tell gcc to never replace conditional load with a non-conditional one