[GVN] Add test for PR63019 (NFC)

(cherry picked from commit 4d64ffa)

Author: nikic

llvm/test/Transforms/GVN/pr63019.ll

@@ -0,0 +1,42 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 2
+; RUN: opt -S -passes=gvn < %s | FileCheck %s
+
+; FIXME: This is a miscompile.
+define i8 @test(i1 %c, i64 %offset, ptr %ptr) {
+; CHECK-LABEL: define i8 @test
+; CHECK-SAME: (i1 [[C:%.*]], i64 [[OFFSET:%.*]], ptr [[PTR:%.*]]) {
+; CHECK-NEXT:  start:
+; CHECK-NEXT:    [[ALLOCA:%.*]] = alloca [8 x i8], align 8
+; CHECK-NEXT:    store i64 1234605616436508552, ptr [[ALLOCA]], align 8
+; CHECK-NEXT:    [[GEP_2:%.*]] = getelementptr i8, ptr [[ALLOCA]], i64 2
+; CHECK-NEXT:    [[GEP_UNKNOWN:%.*]] = getelementptr i8, ptr [[ALLOCA]], i64 [[OFFSET]]
+; CHECK-NEXT:    br i1 [[C]], label [[JOIN:%.*]], label [[IF:%.*]]
+; CHECK:       if:
+; CHECK-NEXT:    br label [[JOIN]]
+; CHECK:       join:
+; CHECK-NEXT:    [[PHI:%.*]] = phi ptr [ [[GEP_UNKNOWN]], [[START:%.*]] ], [ [[GEP_2]], [[IF]] ]
+; CHECK-NEXT:    store i8 0, ptr [[ALLOCA]], align 8
+; CHECK-NEXT:    [[LOAD1:%.*]] = load i64, ptr [[ALLOCA]], align 8
+; CHECK-NEXT:    store i64 [[LOAD1]], ptr [[PTR]], align 8
+; CHECK-NEXT:    [[TMP0:%.*]] = lshr i64 [[LOAD1]], 16
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc i64 [[TMP0]] to i8
+; CHECK-NEXT:    ret i8 [[TMP1]]
+;
+start:
+  %alloca = alloca [8 x i8], align 8
+  store i64 u0x1122334455667788, ptr %alloca, align 8
+  %gep.2 = getelementptr i8, ptr %alloca, i64 2
+  %gep.unknown = getelementptr i8, ptr %alloca, i64 %offset
+  br i1 %c, label %join, label %if
+
+if:
+  br label %join
+
+join:
+  %phi = phi ptr [ %gep.unknown, %start ], [ %gep.2, %if ]
+  store i8 0, ptr %alloca, align 8
+  %load1 = load i64, ptr %alloca, align 8
+  store i64 %load1, ptr %ptr, align 8
+  %load2 = load i8, ptr %phi, align 1
+  ret i8 %load2
+}