[PowerPC] Fix and(or(x, c1), c2) -> rlwimi generation

PPCISelDAGToDAG has a transformation that generates a rlwimi instruction from
an input pattern that looks like this:

  and(or(x, c1), c2)

but the associated logic does not work if there are bits that are 1 in c1 but 0
in c2 (these are normally canonicalized away, but that can't happen if the 'or'
has other users. Make sure we abort the transformation if such bits are
discovered.

Fixes PR24704.

llvm-svn: 246900

1 files changed, 27 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/PowerPC/rlwimi-and-or-bits.ll b/llvm/test/CodeGen/PowerPC/rlwimi-and-or-bits.ll
new file mode 100644
index 00000000000..a74bc727396
--- /dev/null
+++ b/llvm/test/CodeGen/PowerPC/rlwimi-and-or-bits.ll
@@ -0,0 +1,27 @@
+; RUN: llc < %s | FileCheck %s
+target datalayout = "E-m:e-i64:64-n32:64"
+target triple = "powerpc64-unknown-linux-gnu"
+
+@m = external global i32, align 4
+
+; Function Attrs: nounwind
+define signext i32 @main() #0 {
+entry:
+
+; CHECK-LABEL: @main
+; CHECK-NOT: rlwimi
+; CHECK: andi
+
+  %0 = load i32, i32* @m, align 4
+  %or = or i32 %0, 250
+  store i32 %or, i32* @m, align 4
+  %and = and i32 %or, 249
+  %sub.i = sub i32 %and, 0
+  %sext = shl i32 %sub.i, 24
+  %conv = ashr exact i32 %sext, 24
+  ret i32 %conv
+}
+
+attributes #0 = { nounwind "target-cpu"="pwr7" }
+attributes #1 = { nounwind }
+