[clang] [llvm] [AVR] Fix Avr indvar detection and strength reduction (missed optimization) (PR #152028)

[Tom Vijlbrief via llvm-commits]

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@@ -57,7 +57,8 @@ class LLVM_LIBRARY_VISIBILITY AVRTargetInfo : public TargetInfo {
     Int16Type = SignedInt;
     Char32Type = UnsignedLong;
     SigAtomicType = SignedChar;
-    resetDataLayout("e-P1-p:16:8-i8:8-i16:8-i32:8-i64:8-f32:8-f64:8-n8-a:8");
+    resetDataLayout(
+        "e-P1-p:16:8-i8:8-i16:8-i32:8-i64:8-f32:8-f64:8-n8-n16:8-a:8");
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tomtor wrote:

Yes, this change fixes the detection of induction variables. That is a precondition for loop-reduce, but it is also used in other rewrite passes. I think the correct way to proceed is to accept that predec is really a minimal optimization, and if it is no longer generated then that is ok.

https://github.com/llvm/llvm-project/pull/152028