[InstCombine] Merge foldFreezeIntoRecurrence into pushFreezeToPreventPoisonFromPropagating

[c-rhodes]

No description provided.

[c-rhodes]

@zyw-bot csmith-fuzz

[github-actions]

⚠️ undef deprecator found issues in your code. ⚠️

You can test this locally with the following command:

git diff -U0 --pickaxe-regex -S '([^a-zA-Z0-9#_-]undef([^a-zA-Z0-9_-]|$)|UndefValue::get)' 'HEAD~1' HEAD llvm/lib/Transforms/InstCombine/InstructionCombining.cpp llvm/test/Transforms/InstCombine/freeze.ll

The following files introduce new uses of undef:

• llvm/test/Transforms/InstCombine/freeze.ll

Undef is now deprecated and should only be used in the rare cases where no replacement is possible. For example, a load of uninitialized memory yields undef. You should use poison values for placeholders instead.

In tests, avoid using undef and having tests that trigger undefined behavior. If you need an operand with some unimportant value, you can add a new argument to the function and use that instead.

For example, this is considered a bad practice:

define void @fn() {
  ...
  br i1 undef, ...
}

Please use the following instead:

define void @fn(i1 %cond) {
  ...
  br i1 %cond, ...
}

Please refer to the Undefined Behavior Manual for more information.

[c-rhodes]

in the first iteration there were some hangs dtcxzyw/llvm-opt-benchmark#3129, I got a reduced testcase for acv and fixed it with the latest commit.

Re-ran yesterday and there's more hangs: dtcxzyw/llvm-opt-benchmark#3130. I reduced miniz to: https://godbolt.org/z/cTqcxP9j4

it gets stuck in a loop of:

IC: Visiting:   %8 = zext i32 %7 to i64
IC: Mod =   %8 = zext i32 %7 to i64
    New =   %8 = zext nneg i32 %7 to i64
ADD:   %9 = freeze i64 %8
ADD:   %8 = zext nneg i32 %7 to i64
IC: Visiting:   %8 = zext nneg i32 %7 to i64
IC: Visiting:   %9 = freeze i64 %8
ADD DEFERRED:   %8 = zext i32 %7 to i64
ADD DEFERRED:   %7 = lshr i32 %6, 3
ADD DEFERRED:   %6 = add i32 %.2826, -8
ADD:   %8 = zext i32 %7 to i64

which is caused by

llvm-project/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp

Lines 1581 to 1595 in 54b4bd5

	if (!Zext.hasNonNeg()) {
	// If this zero extend is only used by a shift, add nneg flag.
	if (Zext.hasOneUse() &&
	SrcTy->getScalarSizeInBits() >
	Log2_64_Ceil(DestTy->getScalarSizeInBits()) &&
	match(Zext.user_back(), m_Shift(m_Value(), m_Specific(&Zext)))) {
	Zext.setNonNeg();
	return &Zext;
	}
	if (isKnownNonNegative(Src, SQ.getWithInstruction(&Zext))) {
	Zext.setNonNeg();
	return &Zext;
	}
	}

adding nneg then pushFreezeToPreventPoisonFromPropagating dropping it.