[VPlan] Add m_Deferred. NFC

[lukel97]

This copies over the implementation of m_Deferred which allows matching values that were bound in the pattern, and uses it for the (X && Y) || (X && !Y) -> X simplifcation.

[llvmbot]

@llvm/pr-subscribers-vectorizers

@llvm/pr-subscribers-llvm-transforms

Author: Luke Lau (lukel97)

Changes

This copies over the implementation of m_Deferred which allows matching values that were bound in the pattern, and uses it for the (X && Y) || (X && !Y) -> X simplifcation.

---

Full diff: https://github.com/llvm/llvm-project/pull/133736.diff

2 Files Affected:

• (modified) llvm/lib/Transforms/Vectorize/VPlanPatternMatch.h (+21)
• (modified) llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp (+2-3)

diff --git a/llvm/lib/Transforms/Vectorize/VPlanPatternMatch.h b/llvm/lib/Transforms/Vectorize/VPlanPatternMatch.h
index 3a727866a2875..24d1a16d617cf 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanPatternMatch.h
+++ b/llvm/lib/Transforms/Vectorize/VPlanPatternMatch.h
@@ -66,6 +66,27 @@ struct specificval_ty {
 
 inline specificval_ty m_Specific(const VPValue *VPV) { return VPV; }
 
+/// Stores a reference to the VPValue *, not the VPValue * itself,
+/// thus can be used in commutative matchers.
+template <typename Class> struct deferredval_ty {
+  Class *const &Val;
+
+  deferredval_ty(Class *const &V) : Val(V) {}
+
+  template <typename ITy> bool match(ITy *const V) { return V == Val; }
+};
+
+/// Like m_Specific(), but works if the specific value to match is determined
+/// as part of the same match() expression. For example:
+/// m_Mul(m_VPValue(X), m_Specific(X)) is incorrect, because m_Specific() will
+/// bind X before the pattern match starts.
+/// m_Mul(m_VPValue(X), m_Deferred(X)) is correct, and will check against
+/// whichever value m_VPValue(X) populated.
+inline deferredval_ty<VPValue> m_Deferred(VPValue *const &V) { return V; }
+inline deferredval_ty<const VPValue> m_Deferred(const VPValue *const &V) {
+  return V;
+}
+
 /// Match a specified integer value or vector of all elements of that
 /// value. \p BitWidth optionally specifies the bitwidth the matched constant
 /// must have. If it is 0, the matched constant can have any bitwidth.
diff --git a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
index a2e6182cf16e2..372cc5d88ce6c 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
@@ -1049,11 +1049,10 @@ static void simplifyRecipe(VPRecipeBase &R, VPTypeAnalysis &TypeInfo) {
   // TODO: Split up into simpler, modular combines: (X && Y) || (X && Z) into X
   // && (Y || Z) and (X || !X) into true. This requires queuing newly created
   // recipes to be visited during simplification.
-  VPValue *X, *Y, *X1, *Y1;
+  VPValue *X, *Y;
   if (match(&R,
             m_c_BinaryOr(m_LogicalAnd(m_VPValue(X), m_VPValue(Y)),
-                         m_LogicalAnd(m_VPValue(X1), m_Not(m_VPValue(Y1))))) &&
-      X == X1 && Y == Y1) {
+                         m_LogicalAnd(m_Deferred(X), m_Not(m_Deferred(Y)))))) {
     R.getVPSingleValue()->replaceAllUsesWith(X);
     R.eraseFromParent();
     return;

[artagnon]

Some nits; looks good otherwise.

[artagnon]

Mark match function const?

[artagnon]

Is it necessary to match over anything else other than VPValue? Doesn't the name deferredval_ty imply that we're matching a value?

[lukel97]

The template is to allow matching both VPValue and const VPValue, which ties into your review comment below. If we don't think we'll ever need to match a const VPValue I can remove that overload and untemplate this struct.

[artagnon]

IIRC, we don't have a const matcher for m_VPValue(), and considering that m_Deferred() is supposed to be used along with m_VPValue(), I think it's safe to remove the const variant, and un-templatize this.

[lukel97]

Good point about there not being a const m_VPValue(), I've untemplated it now

[artagnon]

Seems like this variant is unnecessary.

[artagnon]

LGTM, thanks!

[fhahn]

LGTM, thanks