[ValueTracking] isKnownNonZero, computeKnownBits for freeze

This implements support for isKnownNonZero, computeKnownBits when freeze is involved.

```
  br (x != 0), BB1, BB2
BB1:
  y = freeze x
```

In the above program, we can say that y is non-zero. The reason is as follows:

(1) If x was poison, `br (x != 0)` raised UB
(2) If x was fully undef, the branch again raised UB
(3) If x was non-zero partially undef, say `undef | 1`, `freeze x` will return a nondeterministic value which is also non-zero.
(4) If x was just a concrete value, it is trivial

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D75808

1 files changed, 18 insertions, 0 deletions

diff --git a/llvm/unittests/Analysis/ValueTrackingTest.cpp b/llvm/unittests/Analysis/ValueTrackingTest.cpp
index 09faad4..c45bca1 100644
--- a/llvm/unittests/Analysis/ValueTrackingTest.cpp
+++ b/llvm/unittests/Analysis/ValueTrackingTest.cpp
@@ -1059,6 +1059,24 @@ TEST_F(ComputeKnownBitsTest, ComputeKnownBitsPtrToIntZext) {
   EXPECT_EQ(Known.One.getZExtValue(), 0u);
 }
 
+TEST_F(ComputeKnownBitsTest, ComputeKnownBitsFreeze) {
+  parseAssembly("define void @test() {\n"
+                "  %m = call i32 @any_num()\n"
+                "  %A = freeze i32 %m\n"
+                "  %n = and i32 %m, 31\n"
+                "  %c = icmp eq i32 %n, 0\n"
+                "  call void @llvm.assume(i1 %c)\n"
+                "  ret void\n"
+                "}\n"
+                "declare void @llvm.assume(i1)\n"
+                "declare i32 @any_num()\n");
+  AssumptionCache AC(*F);
+  KnownBits Known = computeKnownBits(A, M->getDataLayout(), /* Depth */ 0, &AC,
+                                     F->front().getTerminator());
+  EXPECT_EQ(Known.Zero.getZExtValue(), 31u);
+  EXPECT_EQ(Known.One.getZExtValue(), 0u);
+}
+
 class IsBytewiseValueTest : public ValueTrackingTest,
                             public ::testing::WithParamInterface<
                                 std::pair<const char *, const char *>> {