[SimplifyCFG] Add "safe abs" test from CMSIS DSP 'abs_with_clamp()'

With -phi-node-folding-threshold=3
this branch would get flattened into select.

See https://reviews.llvm.org/D65148#1629010

llvm-svn: 368847

1 files changed, 34 insertions, 0 deletions

diff --git a/llvm/test/Transforms/SimplifyCFG/safe-abs.ll b/llvm/test/Transforms/SimplifyCFG/safe-abs.ll
new file mode 100644
index 00000000000..550fcefdde3
--- /dev/null
+++ b/llvm/test/Transforms/SimplifyCFG/safe-abs.ll
@@ -0,0 +1,34 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -simplifycfg -S | FileCheck %s
+
+; Reduced from arm_abs_q31() from CMSIS DSP suite.
+; https://reviews.llvm.org/D65148#1629010
+
+define i32 @abs_with_clamp(i32 %arg) {
+; CHECK-LABEL: @abs_with_clamp(
+; CHECK-NEXT:  begin:
+; CHECK-NEXT:    [[IS_POSITIVE:%.*]] = icmp sgt i32 [[ARG:%.*]], 0
+; CHECK-NEXT:    br i1 [[IS_POSITIVE]], label [[END:%.*]], label [[NEGATIVE:%.*]]
+; CHECK:       negative:
+; CHECK-NEXT:    [[IS_INT_MIN:%.*]] = icmp eq i32 [[ARG]], -2147483648
+; CHECK-NEXT:    [[NEGATED:%.*]] = sub nsw i32 0, [[ARG]]
+; CHECK-NEXT:    [[ABS:%.*]] = select i1 [[IS_INT_MIN]], i32 2147483647, i32 [[NEGATED]]
+; CHECK-NEXT:    br label [[END]]
+; CHECK:       end:
+; CHECK-NEXT:    [[TMP6:%.*]] = phi i32 [ [[ARG]], [[BEGIN:%.*]] ], [ [[ABS]], [[NEGATIVE]] ]
+; CHECK-NEXT:    ret i32 [[TMP6]]
+;
+begin:
+  %is_positive = icmp sgt i32 %arg, 0
+  br i1 %is_positive, label %end, label %negative
+
+negative: ; preds = %begin
+  %is_int_min = icmp eq i32 %arg, -2147483648
+  %negated = sub nsw i32 0, %arg
+  %abs = select i1 %is_int_min, i32 2147483647, i32 %negated
+  br label %end
+
+end:      ; preds = %negative, %begin
+  %tmp6 = phi i32 [ %arg, %begin ], [ %abs, %negative ]
+  ret i32 %tmp6
+}