[PATCH] D128217: [ValueTracking] Teach isKnownNonZero that a vscale is never 0.

[Dave Green via Phabricator via llvm-commits]

dmgreen created this revision.
dmgreen added reviewers: spatel, nikic, paulwalker-arm, david-arm, efriedma.
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A llvm.vscale will always be at least 1, never zero. Teaching that to isKnownNonZero can help fold away some statically known compares.


https://reviews.llvm.org/D128217

Files:
  llvm/lib/Analysis/ValueTracking.cpp
  llvm/test/Transforms/InstCombine/vscale_zero.ll


Index: llvm/test/Transforms/InstCombine/vscale_zero.ll
===================================================================
--- llvm/test/Transforms/InstCombine/vscale_zero.ll
+++ llvm/test/Transforms/InstCombine/vscale_zero.ll
@@ -4,9 +4,7 @@
 define i1 @iszero() {
 ; CHECK-LABEL: @iszero(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[TMP0:%.*]] = call i32 @llvm.vscale.i32()
-; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i32 [[TMP0]], 0
-; CHECK-NEXT:    ret i1 [[TMP1]]
+; CHECK-NEXT:    ret i1 false
 ;
   entry:
   %0 = call i32 @llvm.vscale.i32()
@@ -17,9 +15,7 @@
 define i1 @iszero_range() vscale_range(1,16) {
 ; CHECK-LABEL: @iszero_range(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[TMP0:%.*]] = call i32 @llvm.vscale.i32()
-; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i32 [[TMP0]], 0
-; CHECK-NEXT:    ret i1 [[TMP1]]
+; CHECK-NEXT:    ret i1 false
 ;
   entry:
   %0 = call i32 @llvm.vscale.i32()
Index: llvm/lib/Analysis/ValueTracking.cpp
===================================================================
--- llvm/lib/Analysis/ValueTracking.cpp
+++ llvm/lib/Analysis/ValueTracking.cpp
@@ -2698,6 +2698,9 @@
     if (isKnownNonZero(Op, Depth, Q) &&
         isGuaranteedNotToBePoison(Op, Q.AC, Q.CxtI, Q.DT, Depth))
       return true;
+  } else if (const auto *II = dyn_cast<IntrinsicInst>(V)) {
+    if (II->getIntrinsicID() == Intrinsic::vscale)
+      return true;
   }
 
   KnownBits Known(BitWidth);


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