Update ARMConstantPoolValue to not use a modifier string. Use an explicit

[oota-llvm.git] / lib / Target / ARM / README.txt

diff --git a/lib/Target/ARM/README.txt b/lib/Target/ARM/README.txt
index ba4e5da5a05f881c023d928c7ece1801cd72015a..9fc3fb92cb2c1c4a7a7fc5062d1cfe5c590a8885 100644 (file)
--- a/lib/Target/ARM/README.txt
+++ b/lib/Target/ARM/README.txt
@@ -636,3 +636,24 @@ A custom Thumb version would also be a slight improvement over the generic
 version.
 
 //===---------------------------------------------------------------------===//
+
+Consider the following simple C code:
+
+void foo(unsigned char *a, unsigned char *b, int *c) {
+ if ((*a | *b) == 0) *c = 0;
+}
+
+currently llvm-gcc generates something like this (nice branchless code I'd say):
+
+       ldrb    r0, [r0]
+       ldrb    r1, [r1]
+       orr     r0, r1, r0
+       tst     r0, #255
+       moveq   r0, #0
+       streq   r0, [r2]
+       bx      lr
+
+Note that both "tst" and "moveq" are redundant.
+
+//===---------------------------------------------------------------------===//
+