Fix the issue that ComputeValueKnownInPredecessors only handles the case when
phi is on lhs of a comparison op.
For the following testcase,
L1:
%t0 = add i32 %m, 7
%t3 = icmp eq i32* %t2, null
br i1 %t3, label %L3, label %L2
L2:
%t4 = load i32, i32* %t2, align 4
br label %L3
L3:
%t5 = phi i32 [ %t0, %L1 ], [ %t4, %L2 ]
%t6 = icmp eq i32 %t0, %t5
br i1 %t6, label %L4, label %L5
We know if we go through the path L1 --> L3, %t6 should always be true. However
currently, if the rhs of the eq comparison is phi, JumpThreading fails to
evaluate %t6 to true. And we know that Instcombine cannot guarantee always
canonicalizing phi to the left hand side of the comparison operation according
to the operand priority comparison mechanism in instcombine. The patch handles
the case when rhs of the comparison op is a phi.
Differential Revision: https://reviews.llvm.org/D46275
llvm-svn: 331266
diff --git a/llvm/test/Transforms/JumpThreading/phi-known.ll b/llvm/test/Transforms/JumpThreading/phi-known.ll
index 8eaf57f..3473806 100644
--- a/llvm/test/Transforms/JumpThreading/phi-known.ll
+++ b/llvm/test/Transforms/JumpThreading/phi-known.ll
@@ -64,3 +64,41 @@
ret void
}
+; The eq predicate is always true if we go through the path from
+; L1 to L3, no matter the phi result %t5 is on the lhs or rhs of
+; the predicate.
+declare void @goo()
+declare void @hoo()
+
+define void @test3(i32 %m, i32** %t1) {
+L1:
+ %t0 = add i32 %m, 7
+ %t2 = load i32*, i32** %t1, align 8
+; CHECK-LABEL: @test3
+; CHECK: %t3 = icmp eq i32* %t2, null
+; CHECK: br i1 %t3, label %[[LABEL2:.*]], label %[[LABEL1:.*]]
+
+ %t3 = icmp eq i32* %t2, null
+ br i1 %t3, label %L3, label %L2
+
+; CHECK: [[LABEL1]]:
+; CHECK-NEXT: %t4 = load i32, i32* %t2, align 4
+L2:
+ %t4 = load i32, i32* %t2, align 4
+ br label %L3
+
+L3:
+ %t5 = phi i32 [ %t0, %L1 ], [ %t4, %L2 ]
+ %t6 = icmp eq i32 %t0, %t5
+ br i1 %t6, label %L4, label %L5
+
+; CHECK: [[LABEL2]]:
+; CHECK-NEXT: call void @goo()
+L4:
+ call void @goo()
+ ret void
+
+L5:
+ call void @hoo()
+ ret void
+}