[SCEV] Improve Scalar Evolution's use of no {un,}signed wrap flags

In a case where we have a no {un,}signed wrap flag on the increment, if
RHS - Start is constant then we can avoid inserting a max operation bewteen
the two, since we can statically determine which is greater.

This allows us to unroll loops such as:

 void testcase3(int v) {
   for (int i=v; i<=v+1; ++i)
     f(i);
 }

llvm-svn: 220960

2 files changed, 53 insertions, 2 deletions

diff --git a/llvm/test/Analysis/ScalarEvolution/nsw.ll b/llvm/test/Analysis/ScalarEvolution/nsw.ll
index 05992eadbac..d776a5a5da7 100644
--- a/llvm/test/Analysis/ScalarEvolution/nsw.ll
+++ b/llvm/test/Analysis/ScalarEvolution/nsw.ll
@@ -123,9 +123,8 @@ exit:
   ret i32 %result
 }
 
-; TODO: This could fold down to '1'
 ; CHECK-LABEL: PR12375
-; CHECK: -->  {(4 + %arg),+,4}<nuw><%bb1>		Exits: (4 + (4 * ((-1 + (-1 * %arg) + ((4 + %arg) umax (8 + %arg)<nsw>)) /u 4)) + %arg)
+; CHECK: -->  {(4 + %arg),+,4}<nuw><%bb1>		Exits: (8 + %arg)<nsw>
 define i32 @PR12375(i32* readnone %arg) {
 bb:
   %tmp = getelementptr inbounds i32* %arg, i64 2
@@ -158,3 +157,23 @@ bb2:                                              ; preds = %bb2, %bb
 bb5:                                              ; preds = %bb2
   ret void
 }
+
+declare void @f(i32)
+
+; CHECK-LABEL: nswnowrap
+; CHECK: --> {(1 + %v),+,1}<nsw><%for.body>   Exits: (2 + %v)
+define void @nswnowrap(i32 %v) {
+entry:
+  %add = add nsw i32 %v, 1
+  br label %for.body
+
+for.body:
+  %i.04 = phi i32 [ %v, %entry ], [ %inc, %for.body ]
+  %inc = add nsw i32 %i.04, 1
+  tail call void @f(i32 %i.04)
+  %cmp = icmp slt i32 %i.04, %add
+  br i1 %cmp, label %for.body, label %for.end
+
+for.end:
+  ret void
+}
diff --git a/llvm/test/Transforms/LoopUnroll/nsw-tripcount.ll b/llvm/test/Transforms/LoopUnroll/nsw-tripcount.ll
new file mode 100644
index 00000000000..98cab32a42a
--- /dev/null
+++ b/llvm/test/Transforms/LoopUnroll/nsw-tripcount.ll
@@ -0,0 +1,32 @@
+; 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
+}