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Remove a completed item, add a couple new ones.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@94945 91177308-0d34-0410-b5e6-96231b3b80d8
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Eli Friedman 2010-01-31 04:55:32 +00:00
parent b406c47ea9
commit 1144d7e3cc
1 changed files with 38 additions and 4 deletions
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42
lib/Target/README.txt
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@ -1751,12 +1751,46 @@ from gcc.
Missed instcombine transformation:
define i32 @a(i32 %x) nounwind readnone {
entry:
%shr = lshr i32 %x, 5 ; <i32> [#uses=1]
%xor = xor i32 %shr, 67108864 ; <i32> [#uses=1]
%sub = add i32 %xor, -67108864 ; <i32> [#uses=1]
%rem = srem i32 %x, 32
%shl = shl i32 1, %rem
ret i32 %shl
}
The srem can be transformed to an and because if x is negative, the shift is
undefined. Testcase derived from gcc.
//===---------------------------------------------------------------------===//
Missed instcombine/dagcombine transformation:
define i32 @a(i32 %x, i32 %y) nounwind readnone {
entry:
%mul = mul i32 %y, -8
%sub = sub i32 %x, %mul
ret i32 %sub
}
This function is equivalent to "ashr i32 %x, 5". Testcase derived from gcc.
Should compile to something like x+y*8, but currently compiles to an
inefficient result. Testcase derived from gcc.
//===---------------------------------------------------------------------===//
Missed instcombine/dagcombine transformation:
define void @lshift_lt(i8 zeroext %a) nounwind {
entry:
%conv = zext i8 %a to i32
%shl = shl i32 %conv, 3
%cmp = icmp ult i32 %shl, 33
br i1 %cmp, label %if.then, label %if.end
if.then:
tail call void @bar() nounwind
ret void
if.end:
ret void
}
declare void @bar() nounwind
The shift should be eliminated. Testcase derived from gcc.
//===---------------------------------------------------------------------===//