[PATCH] D67362: [SLP] limit vectorization of Constant subclasses (PR33958)

[Sanjay Patel via Phabricator via llvm-commits]

spatel created this revision.
spatel added reviewers: ABataev, RKSimon, dtemirbulatov.
Herald added subscribers: hiraditya, mcrosier.
Herald added a project: LLVM.

This is a fix for:
https://bugs.llvm.org/show_bug.cgi?id=33958

It seems universally true that we would not want to transform this kind of sequence on any target, but if that's not correct, then we could view this as a target-specific cost model problem. We could also white-list ConstantInt, ConstantFP, etc. rather than blacklist Global and ConstantExpr.


https://reviews.llvm.org/D67362

Files:
  llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
  llvm/test/Transforms/SLPVectorizer/X86/consecutive-access.ll


Index: llvm/test/Transforms/SLPVectorizer/X86/consecutive-access.ll
===================================================================
--- llvm/test/Transforms/SLPVectorizer/X86/consecutive-access.ll
+++ llvm/test/Transforms/SLPVectorizer/X86/consecutive-access.ll
@@ -549,14 +549,17 @@
   br i1 %cmp, label %for.body, label %for.cond.cleanup
 }
 
+; Globals/constant expressions are not normal constants.
+; They should not be treated as the usual vectorization candidates.
+
 @g1 = external global i32, align 4
 @g2 = external global i32, align 4
 
 define void @PR33958(i32** nocapture %p) {
 ; CHECK-LABEL: @PR33958(
-; CHECK-NEXT:    [[ARRAYIDX1:%.*]] = getelementptr inbounds i32*, i32** [[P:%.*]], i64 1
-; CHECK-NEXT:    [[TMP1:%.*]] = bitcast i32** [[P]] to <2 x i32*>*
-; CHECK-NEXT:    store <2 x i32*> <i32* @g1, i32* @g2>, <2 x i32*>* [[TMP1]], align 8
+; CHECK-NEXT:    store i32* @g1, i32** [[P:%.*]], align 8
+; CHECK-NEXT:    [[ARRAYIDX1:%.*]] = getelementptr inbounds i32*, i32** [[P]], i64 1
+; CHECK-NEXT:    store i32* @g2, i32** [[ARRAYIDX1]], align 8
 ; CHECK-NEXT:    ret void
 ;
   store i32* @g1, i32** %p, align 8
Index: llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
===================================================================
--- llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -194,10 +194,13 @@
   return true;
 }
 
-/// \returns True if all of the values in \p VL are constants.
+/// \returns True if all of the values in \p VL are constants (but not
+/// globals/constant expressions).
 static bool allConstant(ArrayRef<Value *> VL) {
+  // Constant expressions and globals can't be vectorized like normal integer/FP
+  // constants.
   for (Value *i : VL)
-    if (!isa<Constant>(i))
+    if (!isa<Constant>(i) || isa<ConstantExpr>(i) || isa<GlobalValue>(i))
       return false;
   return true;
 }


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