[NFC][InstCombine] Add tests for (X - Y) < X --> Y <= X iff Y != 0

https://rise4fun.com/Alive/KtL
This should go to InstCombiner::foldICmpBinO(), next to
"Convert sub-with-unsigned-overflow comparisons into a comparison of args."

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@372911 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/test/Transforms/InstCombine/strict-sub-underflow-check-to-comparison-of-sub-operands.ll b/test/Transforms/InstCombine/strict-sub-underflow-check-to-comparison-of-sub-operands.ll
new file mode 100644 (file)
index 0000000..ceef17a
--- /dev/null
+++ b/test/Transforms/InstCombine/strict-sub-underflow-check-to-comparison-of-sub-operands.ll
@@ -0,0 +1,111 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt %s -instcombine -S | FileCheck %s
+
+declare void @llvm.assume(i1)
+declare i8 @gen8()
+declare void @use8(i8)
+
+define i1 @t0(i8 %base, i8 %offset) {
+; CHECK-LABEL: @t0(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i8 [[OFFSET:%.*]], 0
+; CHECK-NEXT:    call void @llvm.assume(i1 [[CMP]])
+; CHECK-NEXT:    [[ADJUSTED:%.*]] = sub i8 [[BASE:%.*]], [[OFFSET]]
+; CHECK-NEXT:    call void @use8(i8 [[ADJUSTED]])
+; CHECK-NEXT:    [[RES:%.*]] = icmp ult i8 [[ADJUSTED]], [[BASE]]
+; CHECK-NEXT:    ret i1 [[RES]]
+;
+  %cmp = icmp slt i8 %offset, 0
+  call void @llvm.assume(i1 %cmp)
+
+  %adjusted = sub i8 %base, %offset
+  call void @use8(i8 %adjusted)
+  %res = icmp ult i8 %adjusted, %base
+  ret i1 %res
+}
+define i1 @t1(i8 %base, i8 %offset) {
+; CHECK-LABEL: @t1(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i8 [[OFFSET:%.*]], 0
+; CHECK-NEXT:    call void @llvm.assume(i1 [[CMP]])
+; CHECK-NEXT:    [[ADJUSTED:%.*]] = sub i8 [[BASE:%.*]], [[OFFSET]]
+; CHECK-NEXT:    call void @use8(i8 [[ADJUSTED]])
+; CHECK-NEXT:    [[RES:%.*]] = icmp uge i8 [[ADJUSTED]], [[BASE]]
+; CHECK-NEXT:    ret i1 [[RES]]
+;
+  %cmp = icmp slt i8 %offset, 0
+  call void @llvm.assume(i1 %cmp)
+
+  %adjusted = sub i8 %base, %offset
+  call void @use8(i8 %adjusted)
+  %res = icmp uge i8 %adjusted, %base
+  ret i1 %res
+}
+define i1 @t2(i8 %offset) {
+; CHECK-LABEL: @t2(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i8 [[OFFSET:%.*]], 0
+; CHECK-NEXT:    call void @llvm.assume(i1 [[CMP]])
+; CHECK-NEXT:    [[BASE:%.*]] = call i8 @gen8()
+; CHECK-NEXT:    [[ADJUSTED:%.*]] = sub i8 [[BASE]], [[OFFSET]]
+; CHECK-NEXT:    call void @use8(i8 [[ADJUSTED]])
+; CHECK-NEXT:    [[RES:%.*]] = icmp ugt i8 [[BASE]], [[ADJUSTED]]
+; CHECK-NEXT:    ret i1 [[RES]]
+;
+  %cmp = icmp slt i8 %offset, 0
+  call void @llvm.assume(i1 %cmp)
+
+  %base = call i8 @gen8()
+  %adjusted = sub i8 %base, %offset
+  call void @use8(i8 %adjusted)
+  %res = icmp ugt i8 %base, %adjusted
+  ret i1 %res
+}
+define i1 @t3(i8 %offset) {
+; CHECK-LABEL: @t3(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i8 [[OFFSET:%.*]], 0
+; CHECK-NEXT:    call void @llvm.assume(i1 [[CMP]])
+; CHECK-NEXT:    [[BASE:%.*]] = call i8 @gen8()
+; CHECK-NEXT:    [[ADJUSTED:%.*]] = sub i8 [[BASE]], [[OFFSET]]
+; CHECK-NEXT:    call void @use8(i8 [[ADJUSTED]])
+; CHECK-NEXT:    [[RES:%.*]] = icmp ule i8 [[BASE]], [[ADJUSTED]]
+; CHECK-NEXT:    ret i1 [[RES]]
+;
+  %cmp = icmp slt i8 %offset, 0
+  call void @llvm.assume(i1 %cmp)
+
+  %base = call i8 @gen8()
+  %adjusted = sub i8 %base, %offset
+  call void @use8(i8 %adjusted)
+  %res = icmp ule i8 %base, %adjusted
+  ret i1 %res
+}
+
+; Here we don't know that offset is non-zero. Can't fold.
+define i1 @n4_maybezero(i8 %base, i8 %offset) {
+; CHECK-LABEL: @n4_maybezero(
+; CHECK-NEXT:    [[ADJUSTED:%.*]] = sub i8 [[BASE:%.*]], [[OFFSET:%.*]]
+; CHECK-NEXT:    call void @use8(i8 [[ADJUSTED]])
+; CHECK-NEXT:    [[RES:%.*]] = icmp ult i8 [[ADJUSTED]], [[BASE]]
+; CHECK-NEXT:    ret i1 [[RES]]
+;
+  %adjusted = sub i8 %base, %offset
+  call void @use8(i8 %adjusted)
+  %res = icmp ult i8 %adjusted, %base
+  ret i1 %res
+}
+; We need to know that about %offset, %base won't do. Can't fold.
+define i1 @n5_wrongnonzero(i8 %base, i8 %offset) {
+; CHECK-LABEL: @n5_wrongnonzero(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i8 [[BASE:%.*]], 0
+; CHECK-NEXT:    call void @llvm.assume(i1 [[CMP]])
+; CHECK-NEXT:    [[ADJUSTED:%.*]] = sub i8 [[BASE]], [[OFFSET:%.*]]
+; CHECK-NEXT:    call void @use8(i8 [[ADJUSTED]])
+; CHECK-NEXT:    [[RES:%.*]] = icmp ult i8 [[ADJUSTED]], [[BASE]]
+; CHECK-NEXT:    ret i1 [[RES]]
+;
+  %cmp = icmp sgt i8 %base, 0
+  call void @llvm.assume(i1 %cmp)
+
+  %adjusted = sub i8 %base, %offset
+  call void @use8(i8 %adjusted)
+  %res = icmp ult i8 %adjusted, %base
+  ret i1 %res
+}