Commit: 9ac1735205632589b49d87b6fb6c376dc603955b
Author: Sergey Sharybin
Date:   Wed Feb 9 10:44:03 2022 +0100
Branches: blender-v3.1-release
https://developer.blender.org/rB9ac1735205632589b49d87b6fb6c376dc603955b

Fix Cycles compilation on 32bit ARM platform

The rbit instruction is only available starting with ARMv6T2 and
the register prefix is different from what AARCH64 uses.

Separate the 32 and 64 bit ARM branches, add missing ISA checks.

Made sure the code works as intended on macMini with Apple silicon,
and on Raspberry Pi 4 B running 32bit Raspbian OS.

Differential Revision: https://developer.blender.org/D14056

===================================================================

M       intern/cycles/util/math.h

===================================================================

diff --git a/intern/cycles/util/math.h b/intern/cycles/util/math.h
index 2bfd4ba19b6..5f047f6f3f4 100644
--- a/intern/cycles/util/math.h
+++ b/intern/cycles/util/math.h
@@ -935,9 +935,15 @@ ccl_device_inline uint prev_power_of_two(uint x)
 ccl_device_inline uint32_t reverse_integer_bits(uint32_t x)
 {
   /* Use a native instruction if it exists. */
-#if defined(__arm__) || defined(__aarch64__)
+#if defined(__aarch64__) || defined(_M_ARM64)
+  /* Assume the rbit is always available on 64bit ARM architecture. */
   __asm__("rbit %w0, %w1" : "=r"(x) : "r"(x));
   return x;
+#elif defined(__arm__) && ((__ARM_ARCH > 7) || __ARM_ARCH == 6 && 
__ARM_ARCH_ISA_THUMB >= 2)
+  /* This ARM instruction is available in ARMv6T2 and above.
+   * This 32-bit Thumb instruction is available in ARMv6T2 and above. */
+  __asm__("rbit %0, %1" : "=r"(x) : "r"(x));
+  return x;
 #elif defined(__KERNEL_CUDA__)
   return __brev(x);
 #elif defined(__KERNEL_METAL__)

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