[LVI] Add select handling

Teach LVI to handle select instructions in the exact same way it handles PHI nodes.  This is useful since various parts of the optimizer convert PHI nodes into selects and we don't want these transformations to cause inferior optimization.  

Note that this patch does nothing to exploit the implied constraint on the inputs represented by the select condition itself.  That will be a later patch and is blocked on http://reviews.llvm.org/D14476

llvm-svn: 259429

1 files changed, 69 insertions, 0 deletions

diff --git a/llvm/test/Transforms/CorrelatedValuePropagation/select.ll b/llvm/test/Transforms/CorrelatedValuePropagation/select.ll
index be44bdcd921..bad8e6b74f5 100644
--- a/llvm/test/Transforms/CorrelatedValuePropagation/select.ll
+++ b/llvm/test/Transforms/CorrelatedValuePropagation/select.ll
@@ -73,3 +73,72 @@ if.end:
   ret i32 %sel
 ; CHECK: ret i32 1
 }
+
+define i1 @test1(i32* %p, i1 %unknown) {
+; CHECK-LABEL: @test1
+  %pval = load i32, i32* %p
+  %cmp1 = icmp slt i32 %pval, 255
+  br i1 %cmp1, label %next, label %exit
+
+next:
+  %min = select i1 %unknown, i32 %pval, i32 5
+  ;; TODO: This pointless branch shouldn't be neccessary
+  br label %next2
+next2:
+; CHECK-LABEL: next2:
+; CHECK: ret i1 false
+  %res = icmp eq i32 %min, 255
+  ret i1 %res
+
+exit:
+; CHECK-LABEL: exit:
+; CHECK: ret i1 true
+  ret i1 true
+}
+
+; Check that we take a conservative meet
+define i1 @test2(i32* %p, i32 %qval, i1 %unknown) {
+; CHECK-LABEL: test2
+  %pval = load i32, i32* %p
+  %cmp1 = icmp slt i32 %pval, 255
+  br i1 %cmp1, label %next, label %exit
+
+next:
+  %min = select i1 %unknown, i32 %pval, i32 %qval
+  ;; TODO: This pointless branch shouldn't be neccessary
+  br label %next2
+next2:
+; CHECK-LABEL: next2
+; CHECK: ret i1 %res
+  %res = icmp eq i32 %min, 255
+  ret i1 %res
+
+exit:
+; CHECK-LABEL: exit:
+; CHECK: ret i1 true
+  ret i1 true
+}
+
+; Same as @test2, but for the opposite select input
+define i1 @test3(i32* %p, i32 %qval, i1 %unknown) {
+; CHECK-LABEL: test3
+  %pval = load i32, i32* %p
+  %cmp1 = icmp slt i32 %pval, 255
+  br i1 %cmp1, label %next, label %exit
+
+next:
+  %min = select i1 %unknown, i32 %qval, i32 %pval
+  ;; TODO: This pointless branch shouldn't be neccessary
+  br label %next2
+next2:
+; CHECK-LABEL: next2
+; CHECK: ret i1 %res
+  %res = icmp eq i32 %min, 255
+  ret i1 %res
+
+exit:
+; CHECK-LABEL: exit:
+; CHECK: ret i1 true
+  ret i1 true
+}
+