[llvm] [CodeGen] Emit a more efficient magic number multiplication for exact udivs (PR #87161)

[via llvm-commits]

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@@ -5122,6 +5149,29 @@ MachineInstr *CombinerHelper::buildUDivUsingMul(MachineInstr &MI) {
     return true;
   };
 
+  if (MI.getFlag(MachineInstr::MIFlag::IsExact)) {
+    // Collect all magic values from the build vector.
+    bool Matched = matchUnaryPredicate(MRI, RHS, BuildExactUDIVPattern);
+    (void)Matched;
+    assert(Matched && "Expected unary predicate match to succeed");
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AtariDreams wrote:

I am just mirroring the sdiv logic but changing what is necessary. 

https://github.com/llvm/llvm-project/pull/87161