[PATCH] D20544: [ValueTracking, InstSimplify] extend isKnownNonZero() to handle vector constants

[Sanjay Patel via llvm-commits]

spatel created this revision.
spatel added reviewers: majnemer, jmolloy, sanjoy.
spatel added a subscriber: llvm-commits.
Herald added a subscriber: mcrosier.

Similar in spirit to D20497 : 
If all elements of a constant vector are known non-zero, then we can say that the whole vector is known non-zero.
It seems like we could extend this to FP scalar/vector too, but isKnownNonZero() says it only works for integers and pointers for now.

http://reviews.llvm.org/D20544

Files:
  lib/Analysis/ValueTracking.cpp
  test/Transforms/InstSimplify/vec-cmp.ll

Index: test/Transforms/InstSimplify/vec-cmp.ll
===================================================================
--- test/Transforms/InstSimplify/vec-cmp.ll
+++ test/Transforms/InstSimplify/vec-cmp.ll
@@ -1,35 +1,27 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt < %s -instsimplify -S | FileCheck %s
 
-; FIXME: isKnownNonZero should work for integer vectors.
-
 define <2 x i1> @nonzero_vec_splat(<2 x i32> %x) {
 ; CHECK-LABEL: @nonzero_vec_splat(
-; CHECK-NEXT:    [[Y:%.*]] = or <2 x i32> %x, <i32 1, i32 1>
-; CHECK-NEXT:    [[C:%.*]] = icmp eq <2 x i32> [[Y]], zeroinitializer
-; CHECK-NEXT:    ret <2 x i1> [[C]]
+; CHECK-NEXT:    ret <2 x i1> zeroinitializer
 ;
   %y = or <2 x i32> %x, <i32 1, i32 1>
   %c = icmp eq <2 x i32> %y, zeroinitializer
   ret <2 x i1> %c
 }
 
 define <2 x i1> @nonzero_vec_nonsplat(<2 x i32> %x) {
 ; CHECK-LABEL: @nonzero_vec_nonsplat(
-; CHECK-NEXT:    [[Y:%.*]] = or <2 x i32> %x, <i32 2, i32 1>
-; CHECK-NEXT:    [[C:%.*]] = icmp ne <2 x i32> [[Y]], zeroinitializer
-; CHECK-NEXT:    ret <2 x i1> [[C]]
+; CHECK-NEXT:    ret <2 x i1> <i1 true, i1 true>
 ;
   %y = or <2 x i32> %x, <i32 2, i32 1>
   %c = icmp ne <2 x i32> %y, zeroinitializer
   ret <2 x i1> %c
 }
 
 define <2 x i1> @nonzero_vec_undef_elt(<2 x i32> %x) {
 ; CHECK-LABEL: @nonzero_vec_undef_elt(
-; CHECK-NEXT:    [[Y:%.*]] = or <2 x i32> %x, <i32 undef, i32 1>
-; CHECK-NEXT:    [[C:%.*]] = icmp eq <2 x i32> [[Y]], zeroinitializer
-; CHECK-NEXT:    ret <2 x i1> [[C]]
+; CHECK-NEXT:    ret <2 x i1> zeroinitializer
 ;
   %y = or <2 x i32> %x, <i32 undef, i32 1>
   %c = icmp eq <2 x i32> %y, zeroinitializer
@@ -50,11 +42,7 @@
 ; Multiplies of non-zero numbers are non-zero if there is no unsigned overflow.
 define <2 x i1> @nonzero_vec_mul_nuw(<2 x i32> %x, <2 x i32> %y) {
 ; CHECK-LABEL: @nonzero_vec_mul_nuw(
-; CHECK-NEXT:    [[XNZ:%.*]] = or <2 x i32> %x, <i32 1, i32 2>
-; CHECK-NEXT:    [[YNZ:%.*]] = or <2 x i32> %y, <i32 3, i32 undef>
-; CHECK-NEXT:    [[M:%.*]] = mul nuw <2 x i32> [[XNZ]], [[YNZ]]
-; CHECK-NEXT:    [[C:%.*]] = icmp eq <2 x i32> [[M]], zeroinitializer
-; CHECK-NEXT:    ret <2 x i1> [[C]]
+; CHECK-NEXT:    ret <2 x i1> zeroinitializer
 ;
   %xnz = or <2 x i32> %x, <i32 1, i32 2>
   %ynz = or <2 x i32> %y, <i32 3, i32 undef>
@@ -66,11 +54,7 @@
 ; Multiplies of non-zero numbers are non-zero if there is no signed overflow.
 define <2 x i1> @nonzero_vec_mul_nsw(<2 x i32> %x, <2 x i32> %y) {
 ; CHECK-LABEL: @nonzero_vec_mul_nsw(
-; CHECK-NEXT:    [[XNZ:%.*]] = or <2 x i32> %x, <i32 undef, i32 2>
-; CHECK-NEXT:    [[YNZ:%.*]] = or <2 x i32> %y, <i32 3, i32 4>
-; CHECK-NEXT:    [[M:%.*]] = mul nsw <2 x i32> [[XNZ]], [[YNZ]]
-; CHECK-NEXT:    [[C:%.*]] = icmp ne <2 x i32> [[M]], zeroinitializer
-; CHECK-NEXT:    ret <2 x i1> [[C]]
+; CHECK-NEXT:    ret <2 x i1> <i1 true, i1 true>
 ;
   %xnz = or <2 x i32> %x, <i32 undef, i32 2>
   %ynz = or <2 x i32> %y, <i32 3, i32 4>
Index: lib/Analysis/ValueTracking.cpp
===================================================================
--- lib/Analysis/ValueTracking.cpp
+++ lib/Analysis/ValueTracking.cpp
@@ -1678,7 +1678,19 @@
     if (isa<ConstantInt>(C))
       // Must be non-zero due to null test above.
       return true;
-    // TODO: Handle vectors
+
+    // For constant vectors, check that all elements are undefined or known
+    // non-zero to determine that the whole vector is known non-zero.
+    if (auto *VTy = dyn_cast<VectorType>(V->getType())) {
+      for (unsigned i = 0, e = VTy->getNumElements(); i != e; ++i) {
+        Constant *Elt = C->getAggregateElement(i);
+        if (!Elt || Elt->isNullValue() ||
+            (!isa<UndefValue>(Elt) && !isa<ConstantInt>(Elt)))
+          return false;
+      }
+      return true;
+    }
+
     return false;
   }
 


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