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Testcase noticed from PR906

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@30269 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2006-09-11 23:00:56 +00:00
parent 2a33a3f08d
commit 0bfd7fde43
1 changed files with 34 additions and 0 deletions
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34
lib/Target/X86/README.txt
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@ -594,3 +594,37 @@ or eax, 2
cmp eax, 6
jz label
//===---------------------------------------------------------------------===//
Compile:
int %test(ulong *%tmp) {
%tmp = load ulong* %tmp ; <ulong> [#uses=1]
%tmp.mask = shr ulong %tmp, ubyte 50 ; <ulong> [#uses=1]
%tmp.mask = cast ulong %tmp.mask to ubyte ; <ubyte> [#uses=1]
%tmp2 = and ubyte %tmp.mask, 3 ; <ubyte> [#uses=1]
%tmp2 = cast ubyte %tmp2 to int ; <int> [#uses=1]
ret int %tmp2
}
to:
_test:
movl 4(%esp), %eax
movl 4(%eax), %eax
shrl $18, %eax
andl $3, %eax
ret
instead of:
_test:
movl 4(%esp), %eax
movl 4(%eax), %eax
shrl $18, %eax
# TRUNCATE movb %al, %al
andb $3, %al
movzbl %al, %eax
ret
This saves a movzbl, and saves a truncate if it doesn't get coallesced right.
This is a simple DAGCombine to propagate the zext through the and.