[Hexagon] Check for underflow/wrap in hardware loop pass

If the loop trip count may underflow or wrap, the compiler should
not generate a hardware loop since the trip count will be
incorrect.

llvm-svn: 237365

1 files changed, 22 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/Hexagon/hwloop-wrap.ll b/llvm/test/CodeGen/Hexagon/hwloop-wrap.ll
new file mode 100644
index 00000000000..e0f6a87fd2e
--- /dev/null
+++ b/llvm/test/CodeGen/Hexagon/hwloop-wrap.ll
@@ -0,0 +1,22 @@
+; RUN: llc -march=hexagon -mcpu=hexagonv5 < %s | FileCheck %s
+
+; We shouldn't generate a hardware loop in this case because the initial
+; value may be zero, which means the endloop instruction will not decrement
+; the loop counter, and the loop will execute only once.
+
+; CHECK-NOT: loop0
+
+define void @foo(i32 %count, i32 %v) #0 {
+entry:
+  br label %do.body
+
+do.body:
+  %count.addr.0 = phi i32 [ %count, %entry ], [ %dec, %do.body ]
+  tail call void asm sideeffect "nop", ""() #1
+  %dec = add i32 %count.addr.0, -1
+  %cmp = icmp eq i32 %dec, 0
+  br i1 %cmp, label %do.end, label %do.body
+
+do.end:
+  ret void
+}