Remove kill flags after if conversion if necessary

When if converting something like:
true:
   ... = R0<kill>

false:
   ... = R0<kill>

then the instructions of the true block must not have a <kill> flag
anymore, as the instruction of the false block follow and do still read
the R0 value.
Specifically this patch determines the set of register live-in in the
false block (possibly after simulating the liveness changes of the
duplicated instructions). Each of these live-in registers mustn't be
killed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192482 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 30 insertions, 0 deletions

diff --git a/test/CodeGen/ARM/ifconv-kills.ll b/test/CodeGen/ARM/ifconv-kills.ll
new file mode 100644
index 0000000000..bf54ba2f73
--- /dev/null
+++ b/test/CodeGen/ARM/ifconv-kills.ll
@@ -0,0 +1,30 @@
+; RUN: llc < %s -march arm -mcpu swift -verify-machineinstrs
+
+declare i32 @f(i32 %p0, i32 %p1)
+
+define i32 @foo(i32* %ptr) {
+entry:
+  %cmp = icmp ne i32* %ptr, null
+  br i1 %cmp, label %if.then, label %if.else
+
+; present something which can be easily if-converted
+if.then:
+  ; %R0 should be killed here
+  %valt = load i32* %ptr, align 4
+  br label %return
+
+if.else:
+  ; %R0 should be killed here, however after if-conversion the %R0 kill
+  ; has to be removed because if.then will follow after this and still
+  ; read it.
+  %addr = getelementptr inbounds i32* %ptr, i32 4
+  %vale = load i32* %addr, align 4
+  br label %return
+
+return:
+  %phival = phi i32 [ %valt, %if.then ], [ %vale, %if.else ]
+  ; suggest to bring %phival/%valt/%vale into %R1 (because otherwise there
+  ; will be no kills in if.then/if.else)
+  %retval = call i32 @f (i32 0, i32 %phival)
+  ret i32 %retval
+}