[SystemZ] Optimize comparisons with truncated extended loads

If the extension of a loaded value is compared against zero and used in
other arithmetic, InstCombine will change the comparison to use the
unextended load.  It's also possible that the comparison could be against
the unextended load from the outset.

In DAG form this becomes a truncation of an extending load.  We want to
strip the truncation if possible so that we can use load-and-test instructions.

llvm-svn: 197804

1 files changed, 22 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/SystemZ/int-cmp-44.ll b/llvm/test/CodeGen/SystemZ/int-cmp-44.ll
index 8ab67f70e62..822dcac3059 100644
--- a/llvm/test/CodeGen/SystemZ/int-cmp-44.ll
+++ b/llvm/test/CodeGen/SystemZ/int-cmp-44.ll
@@ -865,3 +865,25 @@ store:
 exit:
   ret i32 %res
 }
+
+; A version of f32 that tests the unextended value.
+define i64 @f42(i64 %base, i64 %index, i64 *%dest) {
+; CHECK-LABEL: f42:
+; CHECK: ltgf %r2, 0({{%r2,%r3|%r3,%r2}})
+; CHECK-NEXT: jh .L{{.*}}
+; CHECK: br %r14
+entry:
+  %add = add i64 %base, %index
+  %ptr = inttoptr i64 %add to i32 *
+  %val = load i32 *%ptr
+  %res = sext i32 %val to i64
+  %cmp = icmp sgt i32 %val, 0
+  br i1 %cmp, label %exit, label %store
+
+store:
+  store i64 %res, i64 *%dest
+  br label %exit
+
+exit:
+  ret i64 %res
+}