From 1144d7e3cc27a8bdf4be6bae651c6e8c7d1ec92d Mon Sep 17 00:00:00 2001 From: Eli Friedman Date: Sun, 31 Jan 2010 04:55:32 +0000 Subject: [PATCH] Remove a completed item, add a couple new ones. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@94945 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Target/README.txt | 42 ++++++++++++++++++++++++++++++++++++++---- 1 file changed, 38 insertions(+), 4 deletions(-) diff --git a/lib/Target/README.txt b/lib/Target/README.txt index ce84cbb79d7..7ba7ac90181 100644 --- a/lib/Target/README.txt +++ b/lib/Target/README.txt @@ -1751,12 +1751,46 @@ from gcc. Missed instcombine transformation: define i32 @a(i32 %x) nounwind readnone { entry: - %shr = lshr i32 %x, 5 ; [#uses=1] - %xor = xor i32 %shr, 67108864 ; [#uses=1] - %sub = add i32 %xor, -67108864 ; [#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. //===---------------------------------------------------------------------===//