[llvm] [DA] Add tests where dependencies are missed due to overflow (NFC) (PR #164246)

[Michael Kruse via llvm-commits]

================
@@ -0,0 +1,124 @@
+; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py UTC_ARGS: --version 6
+; RUN: opt < %s -disable-output "-passes=print<da>" 2>&1 \
+; RUN:     | FileCheck %s --check-prefixes=CHECK,CHECK-ALL
+; RUN: opt < %s -disable-output "-passes=print<da>" -da-enable-dependence-test=weak-zero-siv 2>&1 \
+; RUN:     | FileCheck %s --check-prefixes=CHECK,CHECK-WEAK-ZERO-SIV
+
+; offset = -2;
+; for (i = 0; i < (1LL << 62); i++, offset += 2) {
+;   if (0 <= offset)
+;     A[offset] = 1;
+;   A[2] = 2;
+; }
+;
+; FIXME: DependenceAnalysis currently detects no dependency between the two
+; stores, but it does exist. The root cause is that the product of the BTC and
+; the coefficient triggers an overflow.
+;
+define void @weakzero_dst_siv_prod_ovfl(ptr %A) {
+; CHECK-ALL-LABEL: 'weakzero_dst_siv_prod_ovfl'
+; CHECK-ALL-NEXT:  Src: store i8 1, ptr %gep.0, align 1 --> Dst: store i8 1, ptr %gep.0, align 1
+; CHECK-ALL-NEXT:    da analyze - none!
+; CHECK-ALL-NEXT:  Src: store i8 1, ptr %gep.0, align 1 --> Dst: store i8 2, ptr %gep.1, align 1
+; CHECK-ALL-NEXT:    da analyze - none!
+; CHECK-ALL-NEXT:  Src: store i8 2, ptr %gep.1, align 1 --> Dst: store i8 2, ptr %gep.1, align 1
+; CHECK-ALL-NEXT:    da analyze - consistent output [S]!
+;
+; CHECK-WEAK-ZERO-SIV-LABEL: 'weakzero_dst_siv_prod_ovfl'
+; CHECK-WEAK-ZERO-SIV-NEXT:  Src: store i8 1, ptr %gep.0, align 1 --> Dst: store i8 1, ptr %gep.0, align 1
+; CHECK-WEAK-ZERO-SIV-NEXT:    da analyze - consistent output [*]!
+; CHECK-WEAK-ZERO-SIV-NEXT:  Src: store i8 1, ptr %gep.0, align 1 --> Dst: store i8 2, ptr %gep.1, align 1
+; CHECK-WEAK-ZERO-SIV-NEXT:    da analyze - none!
+; CHECK-WEAK-ZERO-SIV-NEXT:  Src: store i8 2, ptr %gep.1, align 1 --> Dst: store i8 2, ptr %gep.1, align 1
+; CHECK-WEAK-ZERO-SIV-NEXT:    da analyze - consistent output [S]!
+;
+entry:
+  br label %loop.header
+
+loop.header:
+  %i = phi i64 [ 0, %entry ], [ %i.inc, %loop.latch ]
+  %offset = phi i64 [ -2, %entry ], [ %offset.next, %loop.latch ]
+  %ec = icmp eq i64 %i, 4611686018427387904
+  br i1 %ec, label %exit, label %loop.body
+
+loop.body:
+  %cond = icmp sge i64 %offset, 0
+  br i1 %cond, label %if.then, label %loop.latch
+
+if.then:
+  %gep.0 = getelementptr inbounds i8, ptr %A, i64 %offset
+  store i8 1, ptr %gep.0
+  br label %loop.latch
+
+loop.latch:
+  %gep.1 = getelementptr inbounds i8, ptr %A, i64 2
+  store i8 2, ptr %gep.1
+  %i.inc = add nuw nsw i64 %i, 1
+  %offset.next = add nsw i64 %offset, 2
+  br label %loop.header
+
+exit:
+  ret void
+}
+
+; offset = -1;
+; for (i = 0; i < n; i++, offset += 2) {
+;   if (0 <= offset)
+;     A[offset] = 1;
+;   A[INT64_MAX] = 2;
+; }
+;
+; FIXME: DependenceAnalysis currently detects no dependency between the two
+; stores, but it does exist. When `%n` is 2^62, the value of `%offset` will be
+; the same as INT64_MAX at the last iteration.
+; The root cause is that the calculation of the differenct between the two
+; constants (INT64_MAX and -1) triggers an overflow.
----------------
Meinersbur wrote:

```suggestion
; The root cause is that the calculation of the difference between the two
; constants (INT64_MAX and -1) overflows.
```

https://github.com/llvm/llvm-project/pull/164246