[IndVarSimplify] Simplify code using preheader assumption

As noted in the nice block comment, the previous code didn't actually handle multi-entry loops correctly, it just assumed SCEV didn't analyze such loops.  Given SCEV has comments to the contrary, that seems a bit suspect.  More importantly, the pass actually requires loopsimplify form which ensures a loop-preheader is available.  Remove the excessive generaility and shorten the code greatly.

Note that we do successfully analyze many multi-entry loops, but we do so by converting them to single entry loops.  See the added test case.

llvm-svn: 316976

1 files changed, 22 insertions, 0 deletions

diff --git a/llvm/test/Transforms/IndVarSimplify/loop-invariant-conditions.ll b/llvm/test/Transforms/IndVarSimplify/loop-invariant-conditions.ll
index eee321da239..1c8eb93869a 100644
--- a/llvm/test/Transforms/IndVarSimplify/loop-invariant-conditions.ll
+++ b/llvm/test/Transforms/IndVarSimplify/loop-invariant-conditions.ll
@@ -273,6 +273,28 @@ for.end:                                          ; preds = %if.end, %entry
   ret void
 }
 
+; check to handle loops without preheaders, but invariant operands
+; (we handle this today by inserting a preheader)
+define void @test9(i1 %cnd, i64 %start) {
+; CHECK-LABEL: @test9
+; CHECK-LABEL: loop.preheader:
+entry:
+  br i1 %cnd, label %entry1, label %entry2
+entry1:
+  br label %loop
+entry2:
+  br label %loop
+loop:
+  %indvars.iv = phi i64 [ %start, %entry1 ],[ %start, %entry2 ], [ %indvars.iv.next, %loop ]
+  %indvars.iv.next = add nsw i64 %indvars.iv, 1
+; CHECK: %cmp1 = icmp slt i64 %start, -1
+  %cmp1 = icmp slt i64 %indvars.iv, -1
+  br i1 %cmp1, label %for.end, label %loop
+
+for.end:                                          ; preds = %if.end, %entry
+  ret void
+}
+
 !1 = !{i64 -1, i64 100}