[llvm] [X86] Create special case for (a-b) - (a<b) -> sbb a, b (PR #161388)

[Simon Pilgrim via llvm-commits]

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@@ -52369,16 +52369,25 @@ static SDValue combineAddOrSubToADCOrSBB(bool IsSub, const SDLoc &DL, EVT VT,
     // Do not flip "e > c", where "c" is a constant, because Cmp instruction
     // cannot take an immediate as its first operand.
     //
-    if (EFLAGS.getOpcode() == X86ISD::SUB && EFLAGS.getNode()->hasOneUse() &&
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RKSimon wrote:

Keep this and add an alt check for `IsSub && X == EFLAGS.getValue(0)` - its better if we don't generate the NewSub node unless we know the folds are going to succeed - we have a lot of oneuse checks below that might get affected by temp nodes that persist for a bit.

https://github.com/llvm/llvm-project/pull/161388