return v ^ (t >> 8);
}
+Neither is this (very standard idiom):
+
+int f(int n)
+{
+ return (((n) << 24) | (((n) & 0xff00) << 8)
+ | (((n) >> 8) & 0xff00) | ((n) >> 24));
+}
+
//===---------------------------------------------------------------------===//
[LOOP RECOGNITION]
//===---------------------------------------------------------------------===//
-From GCC Bug 3756:
-int
-pn (int n)
-{
- return (n >= 0 ? 1 : -1);
-}
-Should combine to (n >> 31) | 1. Currently not optimized with "clang
--emit-llvm-bc | opt -std-compile-opts | llc".
-
-//===---------------------------------------------------------------------===//
-
void a(int variable)
{
if (variable == 4 || variable == 6)
//===---------------------------------------------------------------------===//
-186.crafty contains this interesting pattern:
-
-%77 = call i8* @strstr(i8* getelementptr ([6 x i8]* @"\01LC5", i32 0, i32 0),
- i8* %30)
-%phitmp648 = icmp eq i8* %77, getelementptr ([6 x i8]* @"\01LC5", i32 0, i32 0)
-br i1 %phitmp648, label %bb70, label %bb76
-
-bb70: ; preds = %OptionMatch.exit91, %bb69
- %78 = call i32 @strlen(i8* %30) nounwind readonly align 1 ; <i32> [#uses=1]
-
-This is basically:
- cststr = "abcdef";
- if (strstr(cststr, P) == cststr) {
- x = strlen(P);
- ...
-
-The strstr call would be significantly cheaper written as:
-
-cststr = "abcdef";
-if (memcmp(P, str, strlen(P)))
- x = strlen(P);
-
-This is memcmp+strlen instead of strstr. This also makes the strlen fully
-redundant.
-
-//===---------------------------------------------------------------------===//
-
186.crafty also contains this code:
%1906 = call i32 @strlen(i8* getelementptr ([32 x i8]* @pgn_event, i32 0,i32 0))
(That said, we are doing a lot better than gcc on this testcase. :) )
//===---------------------------------------------------------------------===//
+
+Switch lowering generates less than ideal code for the following switch:
+define void @a(i32 %x) nounwind {
+entry:
+ switch i32 %x, label %if.end [
+ i32 0, label %if.then
+ i32 1, label %if.then
+ i32 2, label %if.then
+ i32 3, label %if.then
+ i32 5, label %if.then
+ ]
+if.then:
+ tail call void @foo() nounwind
+ ret void
+if.end:
+ ret void
+}
+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
+.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
+something like the following, which eliminates a branch:
+ xorl $1, %edi
+ cmpl $4, %edi
+ ja .LBB0_2
+ ret
+.LBB0_2:
+ jmp foo # TAILCALL
+
+//===---------------------------------------------------------------------===//