[SCEV] Fix incorrect trip count computation

The way we elide max expressions when computing trip counts is incorrect
-- it breaks cases like this:

```
static int wrapping_add(int a, int b) {
  return (int)((unsigned)a + (unsigned)b);
}

void test() {
  volatile int end_buf = 2147483548; // INT_MIN - 100
  int end = end_buf;

  unsigned counter = 0;
  for (int start = wrapping_add(end,  200); start < end; start++)
    counter++;

  print(counter);
}
```

Note: the `NoWrap` variable that was being tested has little to do with
the values flowing into the max expression; it is a property of the
induction variable.

test/Transforms/LoopUnroll/nsw-tripcount.ll was added to solely test
functionality I'm reverting in this change, so I've deleted the test
fully.

llvm-svn: 273079

1 files changed, 0 insertions, 32 deletions

diff --git a/llvm/test/Transforms/LoopUnroll/nsw-tripcount.ll b/llvm/test/Transforms/LoopUnroll/nsw-tripcount.ll
deleted file mode 100644
index 98cab32a42a..00000000000
--- a/llvm/test/Transforms/LoopUnroll/nsw-tripcount.ll
+++ /dev/null
@@ -1,32 +0,0 @@
-; RUN: opt -loop-unroll -S %s | FileCheck %s
-
-; extern void f(int);
-; void test1(int v) {
-;   for (int i=v; i<=v+1; ++i)
-;     f(i);
-; }
-;
-; We can use the nsw information to see that the tripcount will be 2, so the
-; loop should be unrolled as this is always beneficial
-
-declare void @f(i32)
-
-; CHECK-LABEL: @test1
-define void @test1(i32 %v) {
-entry:
-  %add = add nsw i32 %v, 1
-  br label %for.body
-
-for.body:
-  %i.04 = phi i32 [ %v, %entry ], [ %inc, %for.body ]
-  tail call void @f(i32 %i.04)
-  %inc = add nsw i32 %i.04, 1
-  %cmp = icmp slt i32 %i.04, %add
-  br i1 %cmp, label %for.body, label %for.end
-
-; CHECK: call void @f
-; CHECK-NOT: br i1
-; CHECK: call void @f
-for.end:
-  ret void
-}