fix a bug (possibly 8816) in the sadd forming xform: it isn't

profitable (or safe) to promote code when the add-with-constant
has other uses.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122175 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/InstCombine/overflow.ll

@@ -1,6 +1,8 @@
 ; RUN: opt -S -instcombine < %s | FileCheck %s
 ; <rdar://problem/8558713>
 
+declare i32 @throwAnExceptionOrWhatever(...)
+
 ; CHECK: @test1
 define i32 @test1(i32 %a, i32 %b) nounwind ssp {
 entry:
@@ -24,4 +26,30 @@ if.end:
   ret i32 %conv9
 }
 
-declare i32 @throwAnExceptionOrWhatever(...)
+; CHECK: @test2
+; This form should not be promoted for two reasons: 1) it is unprofitable to
+; promote it since the add.off instruction has another use, and 2) it is unsafe
+; because the add-with-off makes the high bits of the original add live.
+define i32 @test2(i32 %a, i32 %b, i64* %P) nounwind ssp {
+entry:
+  %conv = sext i32 %a to i64
+  %conv2 = sext i32 %b to i64
+  %add = add nsw i64 %conv2, %conv
+  %add.off = add i64 %add, 2147483648
+  
+  store i64 %add.off, i64* %P
+  
+; CHECK-NOT: llvm.sadd.with.overflow
+  %0 = icmp ugt i64 %add.off, 4294967295
+  br i1 %0, label %if.then, label %if.end
+
+if.then:
+  %call = tail call i32 (...)* @throwAnExceptionOrWhatever() nounwind
+  br label %if.end
+
+if.end:
+  %conv9 = trunc i64 %add to i32
+; CHECK: ret i32
+  ret i32 %conv9
+}
+