recognize an unsigned add with overflow idiom into uadd.

This resolves a README entry and technically resolves PR4916,
but we still get poor code for the testcase in that PR because
GVN isn't CSE'ing uadd with add, filed as PR8817.

Previously we got:

_test7:                                 ## @test7
	addq	%rsi, %rdi
	cmpq	%rdi, %rsi
	movl	$42, %eax
	cmovaq	%rsi, %rax
	ret

Now we get:

_test7:                                 ## @test7
	addq	%rsi, %rdi
	movl	$42, %eax
	cmovbq	%rsi, %rax
	ret



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122182 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 34 insertions, 0 deletions

diff --git a/test/Transforms/InstCombine/overflow.ll b/test/Transforms/InstCombine/overflow.ll
index 6a53d27749..9123283988 100644
--- a/test/Transforms/InstCombine/overflow.ll
+++ b/test/Transforms/InstCombine/overflow.ll
@@ -97,3 +97,37 @@ if.end:                                           ; preds = %entry
 ; CHECK: ret i8
 }
 
+; CHECK: @test5
+; CHECK: llvm.uadd.with.overflow
+; CHECK: ret i64
+define i64 @test5(i64 %a, i64 %b) nounwind ssp {
+entry:
+  %add = add i64 %b, %a
+  %cmp = icmp ult i64 %add, %a
+  %Q = select i1 %cmp, i64 %b, i64 42
+  ret i64 %Q
+}
+
+; CHECK: @test6
+; CHECK: llvm.uadd.with.overflow
+; CHECK: ret i64
+define i64 @test6(i64 %a, i64 %b) nounwind ssp {
+entry:
+  %add = add i64 %b, %a
+  %cmp = icmp ult i64 %add, %b
+  %Q = select i1 %cmp, i64 %b, i64 42
+  ret i64 %Q
+}
+
+; CHECK: @test7
+; CHECK: llvm.uadd.with.overflow
+; CHECK: ret i64
+define i64 @test7(i64 %a, i64 %b) nounwind ssp {
+entry:
+  %add = add i64 %b, %a
+  %cmp = icmp ugt i64 %b, %add
+  %Q = select i1 %cmp, i64 %b, i64 42
+  ret i64 %Q
+}
+
+