[Thumb] Select (CMPZ X, -C) -> (CMPZ (ADDS X, C), 0)
The CMPZ #0 disappears during peepholing, leaving just a tADDi3, tADDi8 or t2ADDri. This avoids having to materialize the expensive negative constant in Thumb-1, and allows a shrinking from a 32-bit CMN to a 16-bit ADDS in Thumb-2.
llvm-svn: 281040
diff --git a/llvm/test/CodeGen/Thumb/cmp-add-fold.ll b/llvm/test/CodeGen/Thumb/cmp-add-fold.ll
new file mode 100644
index 0000000..b0ad8ab
--- /dev/null
+++ b/llvm/test/CodeGen/Thumb/cmp-add-fold.ll
@@ -0,0 +1,32 @@
+; RUN: llc -mtriple=thumbv6m-eabi -verify-machineinstrs < %s | FileCheck --check-prefix=CHECK --check-prefix=T1 %s
+; RUN: llc -mtriple=thumbv7m-eabi -verify-machineinstrs < %s | FileCheck --check-prefix=CHECK --check-prefix=T2 %s
+
+; CHECK-LABEL: addri1:
+; CHECK: adds r0, #3
+; T1-NEXT: b{{eq|ne}}
+; T2-NOT: cmp
+define i32 @addri1(i32 %a, i32 %b) {
+ %c = add i32 %a, 3
+ %d = icmp eq i32 %c, 0
+ br i1 %d, label %true, label %false
+
+true:
+ ret i32 4
+false:
+ ret i32 5
+}
+
+; CHECK-LABEL: addri2:
+; CHECK: adds r0, #254
+; T1-NEXT: b{{eq|ne}}
+; T2-NOT: cmp
+define i32 @addri2(i32 %a, i32 %b) {
+ %c = add i32 %a, 254
+ %d = icmp eq i32 %c, 0
+ br i1 %d, label %true, label %false
+
+true:
+ ret i32 4
+false:
+ ret i32 5
+}