[Xen-devel] [PATCH] xen/arm64: head: Combine lsl and str instructions in a single one

[Julien Grall <julien.grall@xxxxxxx>]

From: Julien Grall <julien.grall@xxxxxxxxxx>

We can optimize a bit the assembly code by combining the 2 instructions
in a single one. This likely not going to make the code faster, but
likely make easier to read the assembly.

Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
---
 xen/arch/arm/arm64/head.S | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
index 0b7f6e7f92..4589a37874 100644
--- a/xen/arch/arm/arm64/head.S
+++ b/xen/arch/arm/arm64/head.S
@@ -418,8 +418,7 @@ skip_bss:
 
         mov   x3, #PT_PT             /* x2 := table map of boot_first_id */
         orr   x2, x2, x3             /*       + rights for linear PT */
-        lsl   x1, x1, #3             /* x1 := Slot offset */
-        str   x2, [x4, x1]
+        str   x2, [x4, x1, lsl #3]
 
         load_paddr x4, boot_first_id
 
@@ -428,8 +427,7 @@ skip_bss:
         mov   x3, #PT_MEM            /* x2 := Section map */
         orr   x2, x2, x3
         and   x1, x1, #LPAE_ENTRY_MASK /* x1 := Slot offset */
-        lsl   x1, x1, #3
-        str   x2, [x4, x1]           /* Mapping of paddr(start) */
+        str   x2, [x4, x1, lsl #3]   /* Mapping of paddr(start) */
         mov   x25, #1                /* x25 := identity map now in place */
 
 1:      /* Setup boot_first: */
@@ -450,8 +448,7 @@ skip_bss:
         lsl   x2, x2, #FIRST_SHIFT   /* Base address for 1GB mapping */
         mov   x3, #PT_MEM            /* x2 := Section map */
         orr   x2, x2, x3
-        lsl   x1, x1, #3             /* x1 := Slot offset */
-        str   x2, [x4, x1]           /* Create mapping of paddr(start)*/
+        str   x2, [x4, x1, lsl #3]   /* Create mapping of paddr(start)*/
         mov   x25, #1                /* x25 := identity map now in place */
 
 1:      /* Setup boot_second: */
@@ -473,8 +470,7 @@ skip_bss:
         lsl   x2, x2, #SECOND_SHIFT  /* Base address for 2MB mapping */
         mov   x3, #PT_MEM            /* x2 := Section map */
         orr   x2, x2, x3
-        lsl   x1, x1, #3             /* x1 := Slot offset */
-        str   x2, [x4, x1]           /* Create mapping of paddr(start)*/
+        str   x2, [x4, x1, lsl #3]   /* Create mapping of paddr(start)*/
         mov   x25, #1                /* x25 := identity map now in place */
 
 1:      /* Setup boot_third: */
-- 
2.11.0


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