[InstSimplify] Simplify llvm.vscale when vscale_range attribute exists

Reduce llvm.vscale to constant based on vscale_range attribute.

Differential Revision: https://reviews.llvm.org/D106850

Author: junparser

llvm/lib/Analysis/InstructionSimplify.cpp

@@ -5772,13 +5772,31 @@ static Value *simplifyBinaryIntrinsic(Function *F, Value *Op0, Value *Op1,
 
 static Value *simplifyIntrinsic(CallBase *Call, const SimplifyQuery &Q) {
 
-  // Intrinsics with no operands have some kind of side effect. Don't simplify.
   unsigned NumOperands = Call->getNumArgOperands();
-  if (!NumOperands)
-    return nullptr;
-
   Function *F = cast<Function>(Call->getCalledFunction());
   Intrinsic::ID IID = F->getIntrinsicID();
+
+  // Most of the intrinsics with no operands have some kind of side effect.
+  // Don't simplify.
+  if (!NumOperands) {
+    switch (IID) {
+    case Intrinsic::vscale: {
+      auto Attr = Call->getFunction()->getFnAttribute(Attribute::VScaleRange);
+      if (!Attr.isValid())
+        return nullptr;
+      unsigned MinScalarVectorSize, MaxScalarVectorSize;
+      std::tie(MinScalarVectorSize, MaxScalarVectorSize) =
+          Attr.getVScaleRangeArgs();
+      if (MinScalarVectorSize == MaxScalarVectorSize &&
+          MaxScalarVectorSize != 0)
+        return ConstantInt::get(F->getReturnType(), MinScalarVectorSize);
+      return nullptr;
+    }
+    default:
+      return nullptr;
+    }
+  }
+
   if (NumOperands == 1)
     return simplifyUnaryIntrinsic(F, Call->getArgOperand(0), Q);
 

llvm/test/Transforms/InstSimplify/fold-vscale.ll

@@ -0,0 +1,40 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -instsimplify -S | FileCheck %s
+
+define i64 @vscale_i64() #1 {
+; CHECK-LABEL: @vscale_i64(
+; CHECK-NEXT:    ret i64 1
+;
+  %out = call i64 @llvm.vscale.i64()
+  ret i64 %out
+}
+
+define i32 @vscale_i32() #2 {
+; CHECK-LABEL: @vscale_i32(
+; CHECK-NEXT:    ret i32 2
+;
+  %out = call i32 @llvm.vscale.i32()
+  ret i32 %out
+}
+
+define i64 @vscale_i64_diff() #3 {
+; CHECK-LABEL: @vscale_i64_diff(
+; CHECK-NEXT:    [[OUT:%.*]] = call i64 @llvm.vscale.i64()
+; CHECK-NEXT:    ret i64 [[OUT]]
+;
+  %out = call i64 @llvm.vscale.i64()
+  ret i64 %out
+}
+
+; Function Attrs: nofree nosync nounwind readnone willreturn
+declare i64 @llvm.vscale.i64() #0
+
+; Function Attrs: nofree nosync nounwind readnone willreturn
+declare i32 @llvm.vscale.i32() #0
+
+attributes #0 = { nofree nosync nounwind readnone willreturn }
+attributes #1 = { mustprogress nofree nosync nounwind uwtable vscale_range(1,1) }
+attributes #2 = { mustprogress nofree nosync nounwind uwtable vscale_range(2,2) }
+attributes #3 = { mustprogress nofree nosync nounwind uwtable vscale_range(2,4) }
+
+