[NoTTI] reject negative scale in addressing mode

Summary:
I noticed this bug when deubging a WIP on LSR. I wonder whether and how we
should add a regression test for this.

Test Plan: no tests failed.

Reviewers: atrick

Subscribers: hfinkel, llvm-commits

Differential Revision: http://reviews.llvm.org/D9536

llvm-svn: 236887

2 files changed, 31 insertions, 3 deletions

diff --git a/llvm/include/llvm/Analysis/TargetTransformInfoImpl.h b/llvm/include/llvm/Analysis/TargetTransformInfoImpl.h
index c6f4f0b3458..3902b0de0a2 100644
--- a/llvm/include/llvm/Analysis/TargetTransformInfoImpl.h
+++ b/llvm/include/llvm/Analysis/TargetTransformInfoImpl.h
@@ -208,9 +208,9 @@ public:
 
   bool isLegalAddressingMode(Type *Ty, GlobalValue *BaseGV, int64_t BaseOffset,
                              bool HasBaseReg, int64_t Scale) {
-    // Guess that reg+reg addressing is allowed. This heuristic is taken from
-    // the implementation of LSR.
-    return !BaseGV && BaseOffset == 0 && Scale <= 1;
+    // Guess that only reg and reg+reg addressing is allowed. This heuristic is
+    // taken from the implementation of LSR.
+    return !BaseGV && BaseOffset == 0 && (Scale == 0 || Scale == 1);
   }
 
   bool isLegalMaskedStore(Type *DataType, int Consecutive) { return false; }
diff --git a/llvm/test/Transforms/LoopStrengthReduce/negative-scale.ll b/llvm/test/Transforms/LoopStrengthReduce/negative-scale.ll
new file mode 100644
index 00000000000..fdde1b6bf9d
--- /dev/null
+++ b/llvm/test/Transforms/LoopStrengthReduce/negative-scale.ll
@@ -0,0 +1,28 @@
+; RUN: opt < %s -loop-reduce -S | FileCheck %s
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
+
+declare void @foo(i8)
+
+define void @not_addressing_mode(i8* %input, i64 %n) {
+; CHECK-LABEL: @not_addressing_mode(
+entry:
+  br label %loop
+
+loop:
+; CHECK: loop:
+; CHECK: %lsr.iv = phi i8* [ {{%[^,]+}}, %loop ], [ %input, %entry ]
+  %i = phi i64 [ 0, %entry ], [ %i.next, %loop ]
+  %i.next = add i64 %i, 1
+  %j = mul i64 %i, -2
+  ; (%input - 2 * %j) is not foldable. Worth another indvar.
+  %p = getelementptr i8, i8* %input, i64 %j
+  %v = load i8, i8* %p
+; CHECK: %v = load i8, i8* %lsr.iv
+  call void @foo(i8 %v)
+  %exitcond = icmp slt i64 %i.next, %n
+  br i1 %exitcond, label %exit, label %loop
+
+exit:
+  ret void
+}