[llvm] [GlobalIsel] Do not run getKnownBits if it is an exact udiv (NFC) (PR #99560)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-globalisel

Author: AtariDreams (AtariDreams)

<details>
<summary>Changes</summary>

This should be better for compile times.

---
Full diff: https://github.com/llvm/llvm-project/pull/99560.diff


1 Files Affected:

- (modified) llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp (+3-1) 


``````````diff
diff --git a/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
index dfc3d73e322b8..a510f40decb84 100644
--- a/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
@@ -5180,7 +5180,9 @@ MachineInstr *CombinerHelper::buildUDivUsingMul(MachineInstr &MI) {
   LLT ScalarShiftAmtTy = ShiftAmtTy.getScalarType();
 
   unsigned KnownLeadingZeros =
-      KB ? KB->getKnownBits(LHS).countMinLeadingZeros() : 0;
+      (!MI.getFlag(MachineInstr::MIFlag::IsExact) && KB)
+          ? KB->getKnownBits(LHS).countMinLeadingZeros()
+          : 0;
   auto &MIB = Builder;
 
   bool UseSRL = false;

``````````

</details>


https://github.com/llvm/llvm-project/pull/99560