[GitHub] [incubator-nuttx] masayuki2009 commented on a change in pull request #5367: armv7-r/a: bugfix: save and restore a4 register in xxx_dcache_all.S

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masayuki2009 commented on a change in pull request #5367:
URL: https://github.com/apache/incubator-nuttx/pull/5367#discussion_r794964791



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File path: arch/arm/src/armv7-a/cp15_clean_dcache_all.S
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@@ -91,12 +91,16 @@
 
 cp15_flush_dcache_all:
 
+	push		{r4}
+
 	mrc		CP15_CCSIDR(r0)			/* Read the Cache Size Identification Register */
+	mov		r4, r0
+
 	ldr		r3, =0x7fff			/* Isolate the NumSets field (bits 13-27) */
 	and		r0, r3, r0, lsr #13		/* r0=NumSets (number of sets - 1) */
 
 	ldr		r3, =0x3ff			/* Isolate the way field (bits 3-12) */
-	add		r4, r3, r0, lsr #3		/* r4=(number of ways - 1) */
+	add		r4, r3, r4, lsr #3		/* r4=(number of ways - 1) */

Review comment:
       @zhuyanlinzyl @xiaoxiang781216 
   I agree to remove r4 and reuse some register (perhaps r1?).
   By the way, I think ```add r4, r3, r0, lsr #3``` means ```r4 = r3 + (r0 >> 3)```.
   I thought it would be ```and r4, r3, r0, lsr #3  (i.e. r4 = r3 & (r0 >> 3)```
   




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