[SCEV] No-wrap flags are not propagated when folding "{S,+,X}+T ==> {S+T,+,X}"

Summary:
**Description**

This makes `WidenIV::widenIVUse` (IndVarSimplify.cpp) fail to widen narrow IV uses in some cases. The latter affects IndVarSimplify which may not eliminate narrow IV's when there actually exists such a possibility, thereby producing ineffective code.

When `WidenIV::widenIVUse` gets a NarrowUse such as `{(-2 + %inc.lcssa),+,1}<nsw><%for.body3>`, it first tries to get a wide recurrence for it via the `getWideRecurrence` call.
`getWideRecurrence` returns recurrence like this: `{(sext i32 (-2 + %inc.lcssa) to i64),+,1}<nsw><%for.body3>`.

Then a wide use operation is generated by `cloneIVUser`. The generated wide use is evaluated to `{(-2 + (sext i32 %inc.lcssa to i64))<nsw>,+,1}<nsw><%for.body3>`, which is different from the `getWideRecurrence` result. `cloneIVUser` sees the difference and returns nullptr.

This patch also fixes the broken LLVM tests by adding missing <nsw> entries introduced by the correction.

**Minimal reproducer:**
```
int foo(int a, int b, int c);
int baz();

void bar()
{
   int arr[20];
   int i = 0;

   for (i = 0; i < 4; ++i)
     arr[i] = baz();

   for (; i < 20; ++i)
     arr[i] = foo(arr[i - 4], arr[i - 3], arr[i - 2]);
}
```

**Clang command line:**
```
clang++ -mllvm -debug -S -emit-llvm -O3 --target=aarch64-linux-elf test.cpp -o test.ir
```

**Expected result:**
The ` -mllvm -debug` log shows that all the IV's for the second `for` loop have been eliminated.

Reviewers: sanjoy

Subscribers: atrick, asl, aemerson, mzolotukhin, llvm-commits

Differential Revision: http://reviews.llvm.org/D20058

llvm-svn: 270695

1 files changed, 3 insertions, 3 deletions

diff --git a/llvm/test/Analysis/ScalarEvolution/flags-from-poison.ll b/llvm/test/Analysis/ScalarEvolution/flags-from-poison.ll
index 8944d2b1a6b..a9d55f1b3db 100644
--- a/llvm/test/Analysis/ScalarEvolution/flags-from-poison.ll
+++ b/llvm/test/Analysis/ScalarEvolution/flags-from-poison.ll
@@ -420,7 +420,7 @@ loop:
 
   %j = add nsw i32 %i, 1
 ; CHECK: %index32 =
-; CHECK: --> {(1 + %offset),+,1}<nsw>
+; CHECK: --> {(1 + %offset)<nsw>,+,1}<nsw>
   %index32 = add nsw i32 %j, %offset
 
   %ptr = getelementptr inbounds float, float* %input, i32 %index32
@@ -562,7 +562,7 @@ loop:
   %i = phi i32 [ %nexti, %loop ], [ %start, %entry ]
 
 ; CHECK: %index32 =
-; CHECK: --> {((-1 * %halfsub)<nsw> + %start),+,1}<nsw>
+; CHECK: --> {((-1 * %halfsub)<nsw> + %start)<nsw>,+,1}<nsw>
   %index32 = sub nsw i32 %i, %halfsub
   %index64 = sext i32 %index32 to i64
 
@@ -621,7 +621,7 @@ loop:
 
   %j = add nsw i32 %i, 1
 ; CHECK: %index32 =
-; CHECK: --> {(1 + (-1 * %offset)),+,1}<nsw>
+; CHECK: --> {(1 + (-1 * %offset))<nsw>,+,1}<nsw>
   %index32 = sub nsw i32 %j, %offset
 
   %ptr = getelementptr inbounds float, float* %input, i32 %index32