[InstCombine] add tests for memcmp with constant; NFC

This is the baseline (current) version of the tests that would
have been added with the transform in r311333 (reverted at 
r311340 due to inf-looping).

Adding these now to aid in testing and minimize the patch if/when
it is reinstated.

llvm-svn: 311350

1 files changed, 51 insertions, 0 deletions

diff --git a/llvm/test/Transforms/InstCombine/memcmp-constant-fold.ll b/llvm/test/Transforms/InstCombine/memcmp-constant-fold.ll
new file mode 100644
index 00000000000..b19f17c818d
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/memcmp-constant-fold.ll
@@ -0,0 +1,51 @@
+; RUN: opt < %s -instcombine -S -data-layout=e-n32 | FileCheck %s --check-prefix=ALL --check-prefix=LE
+; RUN: opt < %s -instcombine -S -data-layout=E-n32 | FileCheck %s --check-prefix=ALL --check-prefix=BE
+
+declare i32 @memcmp(i8*, i8*, i64)
+
+; TODO: The alignment of this constant does not matter. We constant fold the load.
+
+@charbuf = private unnamed_addr constant [4 x i8] [i8 0, i8 0, i8 0, i8 1], align 1
+
+define i1 @memcmp_4bytes_unaligned_constant_i8(i8* align 4 %x) {
+; ALL-LABEL: @memcmp_4bytes_unaligned_constant_i8(
+; ALL-NEXT:    [[CALL:%.*]] = tail call i32 @memcmp(i8* %x, i8* getelementptr inbounds ([4 x i8], [4 x i8]* @charbuf, i64 0, i64 0), i64 4)
+; ALL-NEXT:    [[CMPEQ0:%.*]] = icmp eq i32 [[CALL]], 0
+; ALL-NEXT:    ret i1 [[CMPEQ0]]
+;
+  %call = tail call i32 @memcmp(i8* %x, i8* getelementptr inbounds ([4 x i8], [4 x i8]* @charbuf, i64 0, i64 0), i64 4)
+  %cmpeq0 = icmp eq i32 %call, 0
+  ret i1 %cmpeq0
+}
+
+; TODO: We still don't care about alignment of the constant. We are not limited to constant folding only i8 arrays.
+; It doesn't matter if the constant operand is the first operand to the memcmp.
+
+@intbuf_unaligned = private unnamed_addr constant [4 x i16] [i16 1, i16 2, i16 3, i16 4], align 1
+
+define i1 @memcmp_4bytes_unaligned_constant_i16(i8* align 4 %x) {
+; ALL-LABEL: @memcmp_4bytes_unaligned_constant_i16(
+; ALL-NEXT:    [[CALL:%.*]] = tail call i32 @memcmp(i8* bitcast ([4 x i16]* @intbuf_unaligned to i8*), i8* %x, i64 4)
+; ALL-NEXT:    [[CMPEQ0:%.*]] = icmp eq i32 [[CALL]], 0
+; ALL-NEXT:    ret i1 [[CMPEQ0]]
+;
+  %call = tail call i32 @memcmp(i8* bitcast (i16* getelementptr inbounds ([4 x i16], [4 x i16]* @intbuf_unaligned, i64 0, i64 0) to i8*), i8* %x, i64 4)
+  %cmpeq0 = icmp eq i32 %call, 0
+  ret i1 %cmpeq0
+}
+
+; TODO: Any memcmp where all arguments are constants should be constant folded. Currently, we only handle i8 array constants.
+
+@intbuf = private unnamed_addr constant [2 x i32] [i32 0, i32 1], align 4
+
+define i1 @memcmp_3bytes_aligned_constant_i32(i8* align 4 %x) {
+; ALL-LABEL: @memcmp_3bytes_aligned_constant_i32(
+; ALL-NEXT:    [[CALL:%.*]] = tail call i32 @memcmp(i8* bitcast (i32* getelementptr inbounds ([2 x i32], [2 x i32]* @intbuf, i64 0, i64 1) to i8*), i8* bitcast ([2 x i32]* @intbuf to i8*), i64 3)
+; ALL-NEXT:    [[CMPEQ0:%.*]] = icmp eq i32 [[CALL]], 0
+; ALL-NEXT:    ret i1 [[CMPEQ0]]
+;
+  %call = tail call i32 @memcmp(i8* bitcast (i32* getelementptr inbounds ([2 x i32], [2 x i32]* @intbuf, i64 0, i64 1) to i8*), i8* bitcast (i32* getelementptr inbounds ([2 x i32], [2 x i32]* @intbuf, i64 0, i64 0) to i8*), i64 3)
+  %cmpeq0 = icmp eq i32 %call, 0
+  ret i1 %cmpeq0
+}
+