ReduxWidth check for 0

[gchaltas]

Added assert to check for underflow of ReduxWidth

modified:   llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

Source code analysis flagged the operation (ReduxWwidth - 1) as potential underflow, since ReduxWidth is unsigned.
Realize that this should never happen if everything is working right, but added an assert to check for it just in case.

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[llvmbot]

@llvm/pr-subscribers-llvm-transforms

@llvm/pr-subscribers-vectorizers

Author: George Chaltas (gchaltas)

Changes

Added assert to check for underflow of ReduxWidth

modified:   llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

Source code analysis flagged the operation (ReduxWwidth - 1) as potential underflow, since ReduxWidth is unsigned.
Realize that this should never happen if everything is working right, but added an assert to check for it just in case.

---

Full diff: https://github.com/llvm/llvm-project/pull/123257.diff

1 Files Affected:

• (modified) llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp (+1)

diff --git a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
index b0b8f8249d657b..ae08b0e5a33403 100644
--- a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -20080,6 +20080,7 @@ class HorizontalReduction {
         NumRegs =
             TTI.getNumberOfRegisters(TTI.getRegisterClassForType(true, Tp));
         while (NumParts > NumRegs) {
+	  assert(ReduxWidth > 0 && "ReduxWidth is unexpectedly 0.");
           ReduxWidth = bit_floor(ReduxWidth - 1);
           VectorType *Tp = getWidenedType(ScalarTy, ReduxWidth);
           NumParts = TTI.getNumberOfParts(Tp);

[gchaltas]

@alexey-bataev please review.

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[alexey-bataev]

Format?

[gchaltas]

Oops! Had a tab instead of spaces. Fixed now.

[alexey-bataev]

LG

[gchaltas]

@alexey-bataev would you please merge this?

[github-actions]

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