[Analysis] Fix issues when querying vscale attributes on functions

There are several places in the code that are currently broken as
they assume an Instruction always has a parent Function when
attempting to get the vscale_range attribute. This patch adds checks
that an Instruction has a parent.

I've added a test for a parentless @llvm.vscale intrinsic call here:

  unittests/Analysis/ValueTrackingTest.cpp

Differential Revision: https://reviews.llvm.org/D110158

Author: david-arm

llvm/lib/Analysis/ValueTracking.cpp

@@ -1685,7 +1685,8 @@ static void computeKnownBitsFromOperator(const Operator *I,
           Known.Zero.setBitsFrom(31);
         break;
       case Intrinsic::vscale: {
-        if (!II->getFunction()->hasFnAttribute(Attribute::VScaleRange))
+        if (!II->getParent() ||
+            !II->getFunction()->hasFnAttribute(Attribute::VScaleRange))
           break;
 
         auto VScaleRange = II->getFunction()

llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp

@@ -963,7 +963,8 @@ Instruction *InstCombinerImpl::visitTrunc(TruncInst &Trunc) {
   }
 
   if (match(Src, m_VScale(DL))) {
-    if (Trunc.getFunction()->hasFnAttribute(Attribute::VScaleRange)) {
+    if (Trunc.getFunction() &&
+        Trunc.getFunction()->hasFnAttribute(Attribute::VScaleRange)) {
       unsigned MaxVScale = Trunc.getFunction()
                                ->getFnAttribute(Attribute::VScaleRange)
                                .getVScaleRangeArgs()
@@ -1334,7 +1335,8 @@ Instruction *InstCombinerImpl::visitZExt(ZExtInst &CI) {
   }
 
   if (match(Src, m_VScale(DL))) {
-    if (CI.getFunction()->hasFnAttribute(Attribute::VScaleRange)) {
+    if (CI.getFunction() &&
+        CI.getFunction()->hasFnAttribute(Attribute::VScaleRange)) {
       unsigned MaxVScale = CI.getFunction()
                                ->getFnAttribute(Attribute::VScaleRange)
                                .getVScaleRangeArgs()
@@ -1604,7 +1606,8 @@ Instruction *InstCombinerImpl::visitSExt(SExtInst &CI) {
   }
 
   if (match(Src, m_VScale(DL))) {
-    if (CI.getFunction()->hasFnAttribute(Attribute::VScaleRange)) {
+    if (CI.getFunction() &&
+        CI.getFunction()->hasFnAttribute(Attribute::VScaleRange)) {
       unsigned MaxVScale = CI.getFunction()
                                ->getFnAttribute(Attribute::VScaleRange)
                                .getVScaleRangeArgs()

llvm/unittests/Analysis/ValueTrackingTest.cpp

@@ -12,6 +12,7 @@
 #include "llvm/IR/ConstantRange.h"
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/Function.h"
+#include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/InstIterator.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/LLVMContext.h"
@@ -1597,6 +1598,22 @@ TEST_F(ComputeKnownBitsTest, ComputeKnownBitsAddWithRange) {
   EXPECT_EQ(Known.getMaxValue(), 131071);
 }
 
+TEST_F(ComputeKnownBitsTest, ComputeKnownBitsUnknownVScale) {
+  Module M("", Context);
+  IRBuilder<> Builder(Context);
+  Function *TheFn =
+      Intrinsic::getDeclaration(&M, Intrinsic::vscale, {Builder.getInt32Ty()});
+  CallInst *CI = Builder.CreateCall(TheFn, {}, {}, "");
+
+  KnownBits Known = computeKnownBits(CI, M.getDataLayout(), /* Depth */ 0);
+  delete CI;
+
+  // There is no parent function so we cannot look up the vscale_range
+  // attribute to determine the number of bits.
+  EXPECT_EQ(Known.One.getZExtValue(), 0u);
+  EXPECT_EQ(Known.Zero.getZExtValue(), 0u);
+}
+
 // 512 + [32, 64) doesn't produce overlapping bits.
 // Make sure we get all the individual bits properly.
 TEST_F(ComputeKnownBitsTest, ComputeKnownBitsAddWithRangeNoOverlap) {