[PATCH] ARM: More verbose comments for -mcpu= SIMD CFLAGS

[Loïc Minier]

---
 configure.ac |   12 ++++++++----
 1 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/configure.ac b/configure.ac
index fed97b1..a06f276 100644
--- a/configure.ac
+++ b/configure.ac
@@ -367,15 +367,19 @@ ARM_SIMD_CFLAGS=""
 
 have_arm_simd=no
 AC_MSG_CHECKING(whether to use ARM SIMD assembler)
-# check with default CFLAGS in case the toolchain turns on a sufficiently recent -mcpu=
+# the first -mcpu= to support uqadd8 is arm1136j-s but in ARM mode (not in
+# Thumb mode; it was added with later CPUs in Thumb-2 mode); however the
+# toolchain might be configured for a more recent -march=/-mcpu=, so we first
+# try without any specific CFLAGS (i.e. using the toolchain defaults); only if
+# that doesn't work do we pass -mcpu=arm1136j-s -marm
 AC_COMPILE_IFELSE([
 int main () {
     asm("uqadd8 r1, r1, r2");
     return 0;
 }], have_arm_simd=yes,
-    # check again with an explicit -mcpu= in case the toolchain defaults to an
-    # older one; note that uqadd8 isn't available in Thumb mode on arm1136j-s
-    # so we force ARM mode
+    # check again with an explicit -mcpu= and in ARM mode in case the toolchain
+    # defaults to an older one, or to Thumb mode (uqadd8 isn't available in
+    # Thumb mode on arm1136j-s)
     ARM_SIMD_CFLAGS="-mcpu=arm1136j-s -marm"
     xserver_save_CFLAGS=$CFLAGS
     CFLAGS="$ARM_SIMD_CFLAGS $CFLAGS"
-- 
1.7.0


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