ARC: [mm] micro-optimize page size icache invalidate

start address is already page aligned and size is const PAGE_SIZE,
thus fixups for alignment not needed in generated code.

bloat-o-meter vmlinux-mm5 vmlinux
add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-32 (-32)
function                                     old     new   delta
__inv_icache_page                             82      50     -32
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

arch/arc/mm/cache_arc700.c

@@ -406,9 +406,18 @@ static void __ic_line_inv_vaddr(unsigned long phy_start, unsigned long vaddr,
 	int num_lines, slack;
 	unsigned int addr;
 
-	slack = phy_start & ~ICACHE_LINE_MASK;
-	sz += slack;
-	phy_start -= slack;
+	/*
+	 * Ensure we properly floor/ceil the non-line aligned/sized requests:
+	 * However page sized flushes can be compile time optimised.
+	 *  -@phy_start will be cache-line aligned already (being page aligned)
+	 *  -@sz will be integral multiple of line size (being page sized).
+	 */
+	if (!(__builtin_constant_p(sz) && sz == PAGE_SIZE)) {
+		slack = phy_start & ~ICACHE_LINE_MASK;
+		sz += slack;
+		phy_start -= slack;
+	}
+
 	num_lines = DIV_ROUND_UP(sz, ARC_ICACHE_LINE_LEN);
 
 #if (CONFIG_ARC_MMU_VER > 2)