[AArch64] Fix isLegalAddImmediate() to return true for valid negative values.

Reviewers: t.p.northover, jmolloy

Subscribers: mcrosier, aemerson, llvm-commits, rengolin

Differential Revision: http://reviews.llvm.org/D17463

llvm-svn: 262248

1 files changed, 46 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/AArch64/neg-imm.ll b/llvm/test/CodeGen/AArch64/neg-imm.ll
new file mode 100644
index 00000000000..3ef0392397b
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/neg-imm.ll
@@ -0,0 +1,46 @@
+; RUN: llc -mtriple=aarch64-linux-gnu -verify-machineinstrs -o - %s | FileCheck %s
+; LSR used to pick a sub-optimal solution due to the target responding
+; conservatively to isLegalAddImmediate for negative values.
+
+declare void @foo(i32)
+
+define void @test(i32 %px) {
+; CHECK-LABEL: test:
+; CHECK: // %entry
+; CHECK: subs
+; CHECK-NEXT: csel
+entry:
+  %sub = add nsw i32 %px, -1
+  %cmp = icmp slt i32 %px, 1
+  %.sub = select i1 %cmp, i32 0, i32 %sub
+  br label %for.body
+
+for.body:
+; CHECK: // %for.body
+; CHECK:  cmp
+; CHECK-NEXT:  b.eq
+; CHECK: // %if.then3
+  %x.015 = phi i32 [ %inc, %for.inc ], [ %.sub, %entry ]
+  %cmp2 = icmp eq i32 %x.015, %px
+  br i1 %cmp2, label %for.inc, label %if.then3
+
+if.then3:
+  tail call void @foo(i32 %x.015)
+  br label %for.inc
+
+for.inc:
+; CHECK: // %for.inc
+; CHECK:  add
+; CHECK-NEXT:  cmp
+; CHECK:  b.le
+; CHECK: // %for.cond.cleanup
+  %inc = add nsw i32 %x.015, 1
+  %cmp1 = icmp sgt i32 %x.015, %px
+  br i1 %cmp1, label %for.cond.cleanup.loopexit, label %for.body
+
+for.cond.cleanup.loopexit:
+  br label %for.cond.cleanup
+
+for.cond.cleanup:
+  ret void
+}