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| author | Benjamin Kramer <benny.kra@googlemail.com> | 2011-07-14 01:38:42 +0000 |
|---|---|---|
| committer | Benjamin Kramer <benny.kra@googlemail.com> | 2011-07-14 01:38:42 +0000 |
| commit | 3ff25514ce24a521fc9524eefb257a1f5f262d84 (patch) | |
| tree | bbf4d09b831d59ae312e5b8a3f42dda05b6414c1 /lib/Target/README.txt | |
| parent | d77ec6208cef2a8e615181c2bf0fc5a50a37a20b (diff) | |
| download | llvm-3ff25514ce24a521fc9524eefb257a1f5f262d84.tar.gz llvm-3ff25514ce24a521fc9524eefb257a1f5f262d84.tar.bz2 llvm-3ff25514ce24a521fc9524eefb257a1f5f262d84.tar.xz | |
Don't emit a bit test if there is only one case the test can yield false. A simple SETNE is sufficient.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@135126 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/Target/README.txt')
| -rw-r--r-- | lib/Target/README.txt | 13 |
1 files changed, 4 insertions, 9 deletions
diff --git a/lib/Target/README.txt b/lib/Target/README.txt index 4e382e8f8e..4cc9534089 100644 --- a/lib/Target/README.txt +++ b/lib/Target/README.txt @@ -1762,7 +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 [ @@ -1783,19 +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 |