lib/Target/ARM/CMakeLists.txt: Disable optimization in ARMISelLowering.cpp also on...

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

diff --git a/lib/Target/README.txt b/lib/Target/README.txt
index 260cb5ccab34311d6fc2c6c59568a4eac6d78105..1f69ffb09c0a4a04298f9e84b91acd2b3c06b1ec 100644 (file)
--- a/lib/Target/README.txt
+++ b/lib/Target/README.txt
@@ -870,11 +870,6 @@ rshift_gt (unsigned int a)
    bar ();
 }
 
-void neg_eq_cst(unsigned int a) {
-if (-a == 123)
-bar();
-}
-
 All should simplify to a single comparison.  All of these are
 currently not optimized with "clang -emit-llvm-bc | opt
 -std-compile-opts".
@@ -1767,7 +1762,6 @@ case it choses instead to keep the max operation obvious.
 
 //===---------------------------------------------------------------------===//
 
-Switch lowering generates less than ideal code for the following switch:
 define void @a(i32 %x) nounwind {
 entry:
   switch i32 %x, label %if.end [
@@ -1788,19 +1782,15 @@ declare void @foo()
 Generated code on x86-64 (other platforms give similar results):
 a:
        cmpl    $5, %edi
-       ja      .LBB0_2
-       movl    %edi, %eax
-       movl    $47, %ecx
-       btq     %rax, %rcx
-       jb      .LBB0_3
+       ja      LBB2_2
+       cmpl    $4, %edi
+       jne     LBB2_3
 .LBB0_2:
        ret
 .LBB0_3:
        jmp     foo  # TAILCALL
 
-The movl+movl+btq+jb could be simplified to a cmpl+jne.
-
-Or, if we wanted to be really clever, we could simplify the whole thing to
+If we wanted to be really clever, we could simplify the whole thing to
 something like the following, which eliminates a branch:
        xorl    $1, %edi
        cmpl    $4, %edi
@@ -2353,6 +2343,18 @@ store_bit_field).  The rem should be replaced with a multiply and subtract:
   %3 = sdiv i32 %A, %B
   %4 = srem i32 %A, %B
 
-Similarly for udiv/urem.
+Similarly for udiv/urem.  Note that this shouldn't be done on X86 or ARM,
+which can do this in a single operation (instruction or libcall).  It is
+probably best to do this in the code generator.
+
+//===---------------------------------------------------------------------===//
+
+unsigned foo(unsigned x, unsigned y) { return (x & y) == 0 || x == 0; }
+should fold to (x & y) == 0.
+
+//===---------------------------------------------------------------------===//
+
+unsigned foo(unsigned x, unsigned y) { return x > y && x != 0; }
+should fold to x > y.
 
 //===---------------------------------------------------------------------===//