[clang] [llvm] [InstCombine] Add canonicalization of `sitofp` -> `uitofp nneg` (PR #88299)

[Yingwei Zheng via cfe-commits]

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@@ -1964,11 +1964,25 @@ Instruction *InstCombinerImpl::visitFPToSI(FPToSIInst &FI) {
 }
 
 Instruction *InstCombinerImpl::visitUIToFP(CastInst &CI) {
-  return commonCastTransforms(CI);
+  if (Instruction *R = commonCastTransforms(CI))
+    return R;
+  if (!CI.hasNonNeg() && isKnownNonNegative(CI.getOperand(0), SQ)) {
+    CI.setNonNeg();
+    return &CI;
+  }
+  return nullptr;
 }
 
 Instruction *InstCombinerImpl::visitSIToFP(CastInst &CI) {
-  return commonCastTransforms(CI);
+  if (Instruction *R = commonCastTransforms(CI))
+    return R;
+  if (isKnownNonNegative(CI.getOperand(0), SQ)) {
+    auto UI =
----------------
dtcxzyw wrote:

```suggestion
    auto *UI =
```

https://github.com/llvm/llvm-project/pull/88299