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[SimplifyCFG] Rewrite SinkThenElseCodeToEnd

Description

[SimplifyCFG] Rewrite SinkThenElseCodeToEnd

[Recommitting now an unrelated assertion in SROA is sorted out]

The new version has several advantages:

  1. IMSHO it's more readable and neater
  2. It handles loads and stores properly
  3. It can handle any number of incoming blocks rather than just two. I'll be taking advantage of this in a followup patch.

With this change we can now finally sink load-modify-store idioms such as:

if (a)
  return *b += 3;
else
  return *b += 4;

=>

%z = load i32, i32* %y
%.sink = select i1 %a, i32 5, i32 7
%b = add i32 %z, %.sink
store i32 %b, i32* %y
ret i32 %b

When this works for switches it'll be even more powerful.

Round 4. This time we should handle all instructions correctly, and not replace any operands that need to be constant with variables.

This was really hard to determine safely, so the helper function should be put into the Instruction API. I'll do that as a followup.

Details

Committed
jamesmAug 22 2016, 12:07 PM
Parents
rL279459: [ELF] Only print symbol name when it is available
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