add a random codegen deficiency.
llvm-svn: 77598
diff --git a/llvm/lib/Target/ARM/README.txt b/llvm/lib/Target/ARM/README.txt
index a587a2b..08435c5 100644
--- a/llvm/lib/Target/ARM/README.txt
+++ b/llvm/lib/Target/ARM/README.txt
@@ -546,3 +546,49 @@
Constant island pass should make use of full range SoImm values for LEApcrel.
Be careful though as the last attempt caused infinite looping on lencod.
+
+//===---------------------------------------------------------------------===//
+
+Predication issue. This function:
+
+extern unsigned array[ 128 ];
+int foo( int x ) {
+ int y;
+ y = array[ x & 127 ];
+ if ( x & 128 )
+ y = 123456789 & ( y >> 2 );
+ else
+ y = 123456789 & y;
+ return y;
+}
+
+compiles to:
+
+_foo:
+ and r1, r0, #127
+ ldr r2, LCPI1_0
+ ldr r2, [r2]
+ ldr r1, [r2, +r1, lsl #2]
+ mov r2, r1, lsr #2
+ tst r0, #128
+ moveq r2, r1
+ ldr r0, LCPI1_1
+ and r0, r2, r0
+ bx lr
+
+It would be better to do something like this, to fold the shift into the
+conditional move:
+
+ and r1, r0, #127
+ ldr r2, LCPI1_0
+ ldr r2, [r2]
+ ldr r1, [r2, +r1, lsl #2]
+ tst r0, #128
+ movne r1, r1, lsr #2
+ ldr r0, LCPI1_1
+ and r0, r1, r0
+ bx lr
+
+it saves an instruction and a register.
+
+//===---------------------------------------------------------------------===//