Allow loop unrolling to get known trip counts from ScalarEvolution.

SCEV unrolling can unroll loops with arbitrary induction variables. It
is a prerequisite for -disable-iv-rewrite performance. It is also
easily handles loops of arbitrary structure including multiple exits
and is generally more robust.

This is under a temporary option to avoid affecting default
behavior for the next couple of weeks. It is needed so that I can
checkin unit tests for updateUnloop.

llvm-svn: 137384

1 files changed, 172 insertions, 0 deletions

diff --git a/llvm/test/Transforms/LoopUnroll/scevunroll.ll b/llvm/test/Transforms/LoopUnroll/scevunroll.ll
new file mode 100644
index 00000000000..0f5fbe4e9c2
--- /dev/null
+++ b/llvm/test/Transforms/LoopUnroll/scevunroll.ll
@@ -0,0 +1,172 @@
+; RUN: opt < %s -S -indvars -loop-unroll -verify-loop-info -unroll-scev | FileCheck %s
+;
+; Unit tests for loop unrolling using ScalarEvolution to compute trip counts.
+;
+; Indvars is run first to generate an "old" SCEV result. Some unit
+; tests may check that SCEV is properly invalidated between passes.
+
+; Completely unroll loops without a canonical IV.
+;
+; CHECK: @sansCanonical
+; CHECK-NOT: phi
+; CHECK-NOT: icmp
+; CHECK: ret
+define i32 @sansCanonical(i32* %base) nounwind {
+entry:
+  br label %while.body
+
+while.body:
+  %iv = phi i64 [ 10, %entry ], [ %iv.next, %while.body ]
+  %sum = phi i32 [ 0, %entry ], [ %sum.next, %while.body ]
+  %iv.next = add i64 %iv, -1
+  %adr = getelementptr inbounds i32* %base, i64 %iv.next
+  %tmp = load i32* %adr, align 8
+  %sum.next = add i32 %sum, %tmp
+  %iv.narrow = trunc i64 %iv.next to i32
+  %cmp.i65 = icmp sgt i32 %iv.narrow, 0
+  br i1 %cmp.i65, label %while.body, label %exit
+
+exit:
+  ret i32 %sum
+}
+
+; SCEV unrolling properly handles loops with multiple exits. In this
+; case, the computed trip count based on a canonical IV is *not* for a
+; latch block. Canonical unrolling incorrectly unrolls it, but SCEV
+; unrolling does not.
+;
+; CHECK: @earlyLoopTest
+; CHECK: tail:
+; CHECK-NOT: br
+; CHECK: br i1 %cmp2, label %loop, label %exit2
+define i64 @earlyLoopTest(i64* %base) nounwind {
+entry:
+  br label %loop
+
+loop:
+  %iv = phi i64 [ 0, %entry ], [ %inc, %tail ]
+  %s = phi i64 [ 0, %entry ], [ %s.next, %tail ]
+  %adr = getelementptr i64* %base, i64 %iv
+  %val = load i64* %adr
+  %s.next = add i64 %s, %val
+  %inc = add i64 %iv, 1
+  %cmp = icmp ne i64 %inc, 4
+  br i1 %cmp, label %tail, label %exit1
+
+tail:
+  %cmp2 = icmp ne i64 %val, 0
+  br i1 %cmp2, label %loop, label %exit2
+
+exit1:
+  ret i64 %s
+
+exit2:
+  ret i64 %s.next
+}
+
+; SCEV properly unrolls multi-exit loops.
+;
+; CHECK: @multiExit
+; CHECK: getelementptr i32* %base, i64 10
+; CHECK-NEXT: load i32*
+; CHECK: br i1 false, label %l2.10, label %exit1
+; CHECK: l2.10:
+; CHECK-NOT: br
+; CHECK: ret i32
+define i32 @multiExit(i32* %base) nounwind {
+entry:
+  br label %l1
+l1:
+  %iv1 = phi i32 [ 0, %entry ], [ %inc1, %l2 ]
+  %iv2 = phi i32 [ 0, %entry ], [ %inc2, %l2 ]
+  %inc1 = add i32 %iv1, 1
+  %inc2 = add i32 %iv2, 1
+  %adr = getelementptr i32* %base, i32 %iv1
+  %val = load i32* %adr
+  %cmp1 = icmp slt i32 %iv1, 5
+  br i1 %cmp1, label %l2, label %exit1
+l2:
+  %cmp2 = icmp slt i32 %iv2, 10
+  br i1 %cmp2, label %l1, label %exit2
+exit1:
+  ret i32 1
+exit2:
+  ret i32 %val
+}
+
+
+; SCEV should not unroll a multi-exit loops unless the latch block has
+; a known trip count, regardless of the early exit trip counts. The
+; LoopUnroll utility uses this assumption to optimize the latch
+; block's branch.
+;
+; CHECK: @multiExit
+; CHECK: l3:
+; CHECK-NOT: br
+; CHECK:   br i1 %cmp3, label %l1, label %exit3
+define i32 @multiExitIncomplete(i32* %base) nounwind {
+entry:
+  br label %l1
+l1:
+  %iv1 = phi i32 [ 0, %entry ], [ %inc1, %l3 ]
+  %iv2 = phi i32 [ 0, %entry ], [ %inc2, %l3 ]
+  %inc1 = add i32 %iv1, 1
+  %inc2 = add i32 %iv2, 1
+  %adr = getelementptr i32* %base, i32 %iv1
+  %val = load i32* %adr
+  %cmp1 = icmp slt i32 %iv1, 5
+  br i1 %cmp1, label %l2, label %exit1
+l2:
+  %cmp2 = icmp slt i32 %iv2, 10
+  br i1 %cmp2, label %l3, label %exit2
+l3:
+  %cmp3 = icmp ne i32 %val, 0
+  br i1 %cmp3, label %l1, label %exit3
+
+exit1:
+  ret i32 1
+exit2:
+  ret i32 2
+exit3:
+  ret i32 3
+}
+
+; When loop unroll merges a loop exit with one of its parent loop's
+; exits, SCEV must forget its ExitNotTaken info.
+;
+; CHECK: @nestedUnroll
+; CHECK-NOT: br i1
+; CHECK: for.body87:
+define void @nestedUnroll() nounwind {
+entry:
+  br label %for.inc
+
+for.inc:
+  br i1 false, label %for.inc, label %for.body38.preheader
+
+for.body38.preheader:
+  br label %for.body38
+
+for.body38:
+  %i.113 = phi i32 [ %inc76, %for.inc74 ], [ 0, %for.body38.preheader ]
+  %mul48 = mul nsw i32 %i.113, 6
+  br label %for.body43
+
+for.body43:
+  %j.011 = phi i32 [ 0, %for.body38 ], [ %inc72, %for.body43 ]
+  %add49 = add nsw i32 %j.011, %mul48
+  %sh_prom50 = zext i32 %add49 to i64
+  %inc72 = add nsw i32 %j.011, 1
+  br i1 false, label %for.body43, label %for.inc74
+
+for.inc74:
+  %inc76 = add nsw i32 %i.113, 1
+  br i1 false, label %for.body38, label %for.body87.preheader
+
+for.body87.preheader:
+  br label %for.body87
+
+for.body87:
+  br label %for.body87
+}
+