Start doing the significantly useful part of jump threading: handle cases

where a comparison has a phi input and that phi is a constant.  For example,
stuff like:

  Threading edge through bool from 'bb2149' to 'bb2231' with cost: 1, across block:
bb2237:		; preds = %bb2231, %bb2149
	%tmp2328.rle = phi i32 [ %tmp2232, %bb2231 ], [ %tmp2232439, %bb2149 ]		; <i32> [#uses=2]
	%done.0 = phi i32 [ %done.2, %bb2231 ], [ 0, %bb2149 ]		; <i32> [#uses=1]
	%tmp2239 = icmp eq i32 %done.0, 0		; <i1> [#uses=1]
	br i1 %tmp2239, label %bb2231, label %bb2327

or

bb38.i298:		; preds = %bb33.i295, %bb1693
	%tmp39.i296.rle = phi %struct.ibox* [ null, %bb1693 ], [ %tmp39.i296.rle1109, %bb33.i295 ]		; <%struct.ibox*> [#uses=2]
	%minspan.1.i291.reg2mem.1 = phi i32 [ 32000, %bb1693 ], [ %minspan.0.i288, %bb33.i295 ]		; <i32> [#uses=1]
	%tmp40.i297 = icmp eq %struct.ibox* %tmp39.i296.rle, null		; <i1> [#uses=1]
	br i1 %tmp40.i297, label %implfeeds.exit311, label %bb43.i301

This triggers thousands of times in spec.

llvm-svn: 50110

1 files changed, 30 insertions, 0 deletions

diff --git a/llvm/test/Transforms/JumpThreading/compare.ll b/llvm/test/Transforms/JumpThreading/compare.ll
new file mode 100644
index 00000000000..cbada569aac
--- /dev/null
+++ b/llvm/test/Transforms/JumpThreading/compare.ll
@@ -0,0 +1,30 @@
+; There should be no phi nodes left.
+; RUN: llvm-as < %s | opt -jump-threading -simplifycfg -mem2reg | llvm-dis | not grep {phi i32}
+
+declare i32 @f1()
+declare i32 @f2()
+declare void @f3()
+
+define i32 @test(i1 %cond) {
+	br i1 %cond, label %T1, label %F1
+
+T1:
+	%v1 = call i32 @f1()
+	br label %Merge
+
+F1:
+	%v2 = call i32 @f2()
+	br label %Merge
+
+Merge:
+	%B = phi i32 [%v1, %T1], [12, %F1]
+	%A = icmp ne i32 %B, 42
+	br i1 %A, label %T2, label %F2
+
+T2:
+	call void @f3()
+	ret i32 1
+
+F2:
+	ret i32 0
+}