Don't assume it's safe to transform a loop just because it's dominated by any

comparison. Fixes bug 1598.

llvm-svn: 40866

2 files changed, 19 insertions, 1 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 0039144d897..879347f7f72 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -2387,7 +2387,7 @@ HowManyLessThans(SCEV *LHS, SCEV *RHS, const Loop *L) {
             return UnknownValue;  // Not a comparison against 'n-1'.
         }
         else return UnknownValue;
-      } else if (Cond == ICmpInst::ICMP_ULT)
+      } else
         return UnknownValue;
 
       // cerr << "Computed Loop Trip Count as: " 
diff --git a/llvm/test/Analysis/ScalarEvolution/2007-09-06-MisinterpretBranch.ll b/llvm/test/Analysis/ScalarEvolution/2007-09-06-MisinterpretBranch.ll
new file mode 100644
index 00000000000..e3393d5eed6
--- /dev/null
+++ b/llvm/test/Analysis/ScalarEvolution/2007-09-06-MisinterpretBranch.ll
@@ -0,0 +1,18 @@
+; RUN: llvm-as < %s | opt -indvars -adce -simplifycfg | llvm-dis | grep "icmp s"
+; PR1598
+
+define i32 @f(i32 %a, i32 %b, i32 %x, i32 %y) {
+entry:
+	%tmp3 = icmp eq i32 %a, %b		; <i1> [#uses=1]
+	br i1 %tmp3, label %return, label %bb
+
+bb:		; preds = %bb, %entry
+	%x_addr.0 = phi i32 [ %tmp6, %bb ], [ %x, %entry ]		; <i32> [#uses=1]
+	%tmp6 = add i32 %x_addr.0, 1		; <i32> [#uses=3]
+	%tmp9 = icmp slt i32 %tmp6, %y		; <i1> [#uses=1]
+	br i1 %tmp9, label %bb, label %return
+
+return:		; preds = %bb, %entry
+	%x_addr.1 = phi i32 [ %x, %entry ], [ %tmp6, %bb ]		; <i32> [#uses=1]
+	ret i32 %x_addr.1
+}