[llvm] [InstCombine] Remove redundant fptrunc of select fold (NFCI) (PR #117182)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Nikita Popov (nikic)

<details>
<summary>Changes</summary>

This was subsumed by FoldOpIntoSelect() in #<!-- -->116073, and has incorrect FMF propagation on top.

---
Full diff: https://github.com/llvm/llvm-project/pull/117182.diff


1 Files Affected:

- (modified) llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp (-18) 


``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 6c2554ea73b7f8..c97be6ffc75675 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -1866,24 +1866,6 @@ Instruction *InstCombinerImpl::visitFPTrunc(FPTruncInst &FPT) {
 
       return UnaryOperator::CreateFNegFMF(InnerTrunc, Op);
     }
-
-    // If we are truncating a select that has an extended operand, we can
-    // narrow the other operand and do the select as a narrow op.
-    Value *Cond, *X, *Y;
-    if (match(Op, m_Select(m_Value(Cond), m_FPExt(m_Value(X)), m_Value(Y))) &&
-        X->getType() == Ty) {
-      // fptrunc (select Cond, (fpext X), Y --> select Cond, X, (fptrunc Y)
-      Value *NarrowY = Builder.CreateFPTrunc(Y, Ty);
-      Value *Sel = Builder.CreateSelect(Cond, X, NarrowY, "narrow.sel", Op);
-      return replaceInstUsesWith(FPT, Sel);
-    }
-    if (match(Op, m_Select(m_Value(Cond), m_Value(Y), m_FPExt(m_Value(X)))) &&
-        X->getType() == Ty) {
-      // fptrunc (select Cond, Y, (fpext X) --> select Cond, (fptrunc Y), X
-      Value *NarrowY = Builder.CreateFPTrunc(Y, Ty);
-      Value *Sel = Builder.CreateSelect(Cond, NarrowY, X, "narrow.sel", Op);
-      return replaceInstUsesWith(FPT, Sel);
-    }
   }
 
   if (auto *II = dyn_cast<IntrinsicInst>(FPT.getOperand(0))) {

``````````

</details>


https://github.com/llvm/llvm-project/pull/117182