Be more aggressive in doing LoadPRE by tracing backwards when a block only has

a single predecessor.

Patch by Jakub Staszak.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@72661 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 32 insertions, 0 deletions

diff --git a/test/Transforms/GVN/pre-single-pred.ll b/test/Transforms/GVN/pre-single-pred.ll
new file mode 100644
index 0000000..b735ea9
--- /dev/null
+++ b/test/Transforms/GVN/pre-single-pred.ll
@@ -0,0 +1,32 @@
+; RUN: llvm-as < %s | opt -gvn -enable-load-pre | llvm-dis | not grep {tmp3 = load}
+
+define i32 @f(i32* nocapture %p, i32 %n) nounwind {
+entry:
+	br label %for.cond
+
+for.cond:		; preds = %for.inc, %entry
+	%i.0 = phi i32 [ 0, %entry ], [ %indvar.next, %for.inc ]		; <i32> [#uses=2]
+	%cmp = icmp slt i32 %i.0, %n		; <i1> [#uses=1]
+	br i1 %cmp, label %for.body, label %for.cond.for.end_crit_edge
+
+for.cond.for.end_crit_edge:		; preds = %for.cond
+	br label %for.end
+
+for.body:		; preds = %for.cond
+	%tmp3 = load i32* %p		; <i32> [#uses=1]
+	%dec = add i32 %tmp3, -1		; <i32> [#uses=2]
+	store i32 %dec, i32* %p
+	%cmp6 = icmp slt i32 %dec, 0		; <i1> [#uses=1]
+	br i1 %cmp6, label %for.body.for.end_crit_edge, label %for.inc
+
+for.body.for.end_crit_edge:		; preds = %for.body
+	br label %for.end
+
+for.inc:		; preds = %for.body
+	%indvar.next = add i32 %i.0, 1		; <i32> [#uses=1]
+	br label %for.cond
+
+for.end:		; preds = %for.body.for.end_crit_edge, %for.cond.for.end_crit_edge
+	%tmp9 = load i32* %p		; <i32> [#uses=1]
+	ret i32 %tmp9
+}