[llvm] Fix profile metadata propagation in InstCombine select folding (PR #179743)

[Mircea Trofin via llvm-commits]

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@@ -3717,28 +3717,32 @@ Instruction *InstCombinerImpl::foldSelectOfBools(SelectInst &SI) {
   // select (~a | c), a, b -> select a, (select c, true, b), false
   if (match(CondVal,
             m_OneUse(m_c_Or(m_Not(m_Specific(TrueVal)), m_Value(C))))) {
-    Value *OrV = Builder.CreateSelect(C, One, FalseVal);
-    return SelectInst::Create(TrueVal, OrV, Zero);
+    Instruction *MDFrom = ProfcheckDisableMetadataFixes ? nullptr : &SI;
+    Value *OrV = Builder.CreateSelect(C, One, FalseVal, "", MDFrom);
+    return SelectInst::Create(TrueVal, OrV, Zero, "", nullptr, MDFrom);
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mtrofin wrote:

`unknown` makes most sense. We could think briefly if knowing `P(~a|c)` tells us anything about the bounds of either `P(a)` or `P(c)`... I guess if `P(~a|c)` < 0.5, neither probabilities `P(~a)` nor `P(c)` could be greater, so maybe under that condition we could copy the original probability to `c` and (flipped) to `a` as it's more accurate.

https://github.com/llvm/llvm-project/pull/179743