Hi,
I met an issue caused by Simplify the CFG. We have the following instructions:
sw.bb: ; preds = %if.then63
%bf.load65 = load i192, i192* %13, align 4
%bf.lshr66 = lshr i192 %bf.load65, 80
sw.bb70: ; preds = %if.then63
%bf.load73 = load i192, i192* %15, align 4
%bf.lshr74 = lshr i192 %bf.load73, 96
sw.bb78: ; preds = %if.then63
%bf.load81 = load i192, i192* %17, align 4
%bf.lshr82 = lshr i192 %bf.load81, 112
sw.bb86: ; preds = %if.then63
%bf.load89 = load i192, i192* %19, align 4
%bf.lshr90 = lshr i192 %bf.load89, 128
sw.bb94: ; preds = %if.then63
%bf.load97 = load i192, i192* %21, align 4
%bf.lshr98 = lshr i192 %bf.load97, 144
Each pair of them is from different blocks and will be sunk into an end block.
Also, a PHI node %.sink is created for the constant operand of lshr as
sw.epilog.sink.split: ; preds = %if.then63, %sw.bb,
%sw.bb78, %sw.bb86, %sw.bb94
%.sink = phi i192 [ 144, %sw.bb94 ], [ 128, %sw.bb86 ], [ 112, %sw.bb78 ], [
80, %sw.bb ], [ 96, %if.then63 ]
%bf.load97 = load i192, i192* %13, align 4
%bf.lshr98 = lshr i192 %bf.load97, %.sink
Before lshr nodes are sunk, our lowering backend can understand which 32 bits of
i192 are need and load that 32 bits only.
But after this CFG pass, %.sink is unknown, then there will be i192 load (8
32-bit loads).
I have some ideas how to handle it, but still I would like some feedback about
what’s best way to do.
(The LLVM IR before and after CFG are shown below)
Thank you.
Best regards,
Ning Xie
*** Before simplify CFG is applied, we have the following LLVM IR ***
if.then63: ; preds = %if.end
%trunc = trunc i8 %11 to i3
switch i3 %trunc, label %sw.epilog [
i3 0, label %sw.bb
i3 1, label %sw.bb70
i3 2, label %sw.bb78
i3 3, label %sw.bb86
i3 -4, label %sw.bb94
]
sw.bb: ; preds = %if.then63
%13 = getelementptr inbounds %struct.C0000294C, %struct.C0000294C* %C0000159C,
i32 0, i32 5, i32 3, i32 %conv50, i32 0
%bf.load65 = load i192, i192* %13, align 4
%bf.lshr66 = lshr i192 %bf.load65, 80
%14 = trunc i192 %bf.lshr66 to i32
%bf.cast68 = and i32 %14, 4095
br label %sw.epilog
sw.bb70: ; preds = %if.then63
%15 = getelementptr inbounds %struct.C0000294C, %struct.C0000294C* %C0000159C,
i32 0, i32 5, i32 3, i32 %conv50, i32 0
%bf.load73 = load i192, i192* %15, align 4
%bf.lshr74 = lshr i192 %bf.load73, 96
%16 = trunc i192 %bf.lshr74 to i32
%bf.cast76 = and i32 %16, 4095
br label %sw.epilog
sw.bb78: ; preds = %if.then63
%17 = getelementptr inbounds %struct.C0000294C, %struct.C0000294C* %C0000159C,
i32 0, i32 5, i32 3, i32 %conv50, i32 0
%bf.load81 = load i192, i192* %17, align 4
%bf.lshr82 = lshr i192 %bf.load81, 112
%18 = trunc i192 %bf.lshr82 to i32
%bf.cast84 = and i32 %18, 4095
br label %sw.epilog
sw.bb86: ; preds = %if.then63
%19 = getelementptr inbounds %struct.C0000294C, %struct.C0000294C* %C0000159C,
i32 0, i32 5, i32 3, i32 %conv50, i32 0
%bf.load89 = load i192, i192* %19, align 4
%bf.lshr90 = lshr i192 %bf.load89, 128
%20 = trunc i192 %bf.lshr90 to i32
%bf.cast92 = and i32 %20, 4095
sw.bb94: ; preds = %if.then63
%21 = getelementptr inbounds %struct.C0000294C, %struct.C0000294C* %C0000159C,
i32 0, i32 5, i32 3, i32 %conv50, i32 0
%bf.load97 = load i192, i192* %21, align 4
%bf.lshr98 = lshr i192 %bf.load97, 144
%22 = trunc i192 %bf.lshr98 to i32
%bf.cast100 = and i32 %22, 4095
br label %sw.epilog
*** IR Dump After Simplify the CFG ***
if.then63: ; preds = %if.end
%trunc = trunc i8 %11 to i3
switch i3 %trunc, label %sw.epilog [
i3 0, label %sw.bb
i3 1, label %sw.epilog.sink.split
i3 2, label %sw.bb78
i3 3, label %sw.bb86
i3 -4, label %sw.bb94
]
sw.bb: ; preds = %if.then63
br label %sw.epilog.sink.split
sw.bb78: ; preds = %if.then63
br label %sw.epilog.sink.split
sw.bb86: ; preds = %if.then63
br label %sw.epilog.sink.split
sw.bb94: ; preds = %if.then63
br label %sw.epilog.sink.split
sw.epilog.sink.split: ; preds = %if.then63, %sw.bb,
%sw.bb78, %sw.bb86, %sw.bb94
%.sink = phi i192 [ 144, %sw.bb94 ], [ 128, %sw.bb86 ], [ 112, %sw.bb78 ], [
80, %sw.bb ], [ 96, %if.then63 ]
%13 = getelementptr inbounds %struct.C0000294C, %struct.C0000294C* %C0000159C,
i32 0, i32 5, i32 3, i32 %conv50, i32 0
%bf.load97 = load i192, i192* %13, align 4
%bf.lshr98 = lshr i192 %bf.load97, %.sink
%14 = trunc i192 %bf.lshr98 to i32
%bf.cast100 = and i32 %14, 4095
br label %sw.epilog
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20170802/a8530e21/attachment-0001.html>