[PowerPC] Better lowering for add/or of a FrameIndex

If we have an add (or an or that is really an add), where one operand is a
FrameIndex and the other operand is a small constant, we can combine the
lowering of the FrameIndex (which is lowered as an add of the FI and a zero
offset) with the constant operand.

Amusingly, this is an old potential improvement entry from
lib/Target/PowerPC/README.txt which had never been resolved. In short, we used
to lower:

        %X = alloca { i32, i32 }
        %Y = getelementptr {i32,i32}* %X, i32 0, i32 1
        ret i32* %Y

as:

        addi 3, 1, -8
        ori 3, 3, 4
        blr

and now we produce:

        addi 3, 1, -4
        blr

which is much more sensible.

llvm-svn: 224071

1 files changed, 24 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/PowerPC/add-fi.ll b/llvm/test/CodeGen/PowerPC/add-fi.ll
new file mode 100644
index 00000000000..18892c8cdf5
--- /dev/null
+++ b/llvm/test/CodeGen/PowerPC/add-fi.ll
@@ -0,0 +1,24 @@
+; RUN: llc -mcpu=ppc64 < %s | FileCheck %s
+target datalayout = "E-m:e-i64:64-n32:64"
+target triple = "powerpc64-unknown-linux-gnu"
+
+define i32* @test1() {
+        %X = alloca { i32, i32 }
+        %Y = getelementptr {i32,i32}* %X, i32 0, i32 1
+        ret i32* %Y
+
+; CHECK-LABEL: @test1
+; CHECK: addi 3, 1, -4
+; CHECK: blr
+}
+
+define i32* @test2() {
+        %X = alloca { i32, i32, i32, i32 }
+        %Y = getelementptr {i32,i32,i32,i32}* %X, i32 0, i32 3
+        ret i32* %Y
+
+; CHECK-LABEL: @test2
+; CHECK: addi 3, 1, -4
+; CHECK: blr
+}
+