[LLE] Don't hoist conditionally executed loads

If the load is conditional we can't hoist its 0-iteration instance to
the preheader because that would make it unconditional.  Thus we would
access a memory location that the original loop did not access.

llvm-svn: 273991

1 files changed, 42 insertions, 0 deletions

diff --git a/llvm/test/Transforms/LoopLoadElim/cond-load.ll b/llvm/test/Transforms/LoopLoadElim/cond-load.ll
new file mode 100644
index 00000000000..e337397e996
--- /dev/null
+++ b/llvm/test/Transforms/LoopLoadElim/cond-load.ll
@@ -0,0 +1,42 @@
+; RUN: opt -S -loop-load-elim < %s | FileCheck %s
+
+; We can't hoist conditional loads to the preheader for the initial value.
+; E.g. in the loop below we'd access array[-1] if we did:
+;
+;   for(int i = 0 ; i < n ; i++ )
+;     array[i] = ( i > 0 ? array[i - 1] : 0 ) + 4;
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.11.0"
+
+define void @f(i32* %array, i32 %n) {
+entry:
+  %cmp10 = icmp sgt i32 %n, 0
+  br i1 %cmp10, label %for.body, label %for.cond.cleanup
+
+for.cond.cleanup:                                 ; preds = %cond.end, %entry
+  ret void
+
+for.body:                                         ; preds = %entry, %cond.end
+  %indvars.iv = phi i64 [ %indvars.iv.next, %cond.end ], [ 0, %entry ]
+; CHECK-NOT: %store_forwarded = phi
+  %cmp1 = icmp sgt i64 %indvars.iv, 0
+  br i1 %cmp1, label %cond.true, label %cond.end
+
+cond.true:                                        ; preds = %for.body
+  %0 = add nsw i64 %indvars.iv, -1
+  %arrayidx = getelementptr inbounds i32, i32* %array, i64 %0
+  %1 = load i32, i32* %arrayidx, align 4
+  br label %cond.end
+
+cond.end:                                         ; preds = %for.body, %cond.true
+  %cond = phi i32 [ %1, %cond.true ], [ 0, %for.body ]
+; CHECK: %cond = phi i32 [ %1, %cond.true ], [ 0, %for.body ]
+  %add = add nsw i32 %cond, 4
+  %arrayidx3 = getelementptr inbounds i32, i32* %array, i64 %indvars.iv
+  store i32 %add, i32* %arrayidx3, align 4
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %lftr.wideiv = trunc i64 %indvars.iv.next to i32
+  %exitcond = icmp eq i32 %lftr.wideiv, %n
+  br i1 %exitcond, label %for.cond.cleanup, label %for.body
+}