[llvm] [InstCombine] Canonicalize the fcmp range check idiom into `fabs + fcmp` (PR #76367)

[Matt Arsenault via llvm-commits]

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@@ -1457,6 +1457,37 @@ Value *InstCombinerImpl::foldLogicOfFCmps(FCmpInst *LHS, FCmpInst *RHS,
     }
   }
 
+  // Canonicalize the range check idiom:
+  // and (fcmp olt/ole/ult/ule x, C), (fcmp ogt/oge/ugt/uge x, -C)
+  // --> fabs(x) olt/ole/ult/ule C
+  // or  (fcmp ogt/oge/ugt/uge x, C), (fcmp olt/ole/ult/ule x, -C)
+  // --> fabs(x) ogt/oge/ugt/uge C
+  // TODO: Generalize to handle a negated variable operand?
+  const APFloat *LHSC, *RHSC;
+  if (LHS->hasOneUse() && RHS->hasOneUse() && LHS0 == RHS0 &&
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arsenm wrote:

Check LHS0 == RHS0 first?

https://github.com/llvm/llvm-project/pull/76367