teach GVN's load PRE to insert computations of the address in predecessors

where it is not available.  It's unclear how to get this inserted 
computation into GVN's scalar availability sets, Owen, help? :)


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@89997 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 34 insertions, 0 deletions

diff --git a/test/Transforms/GVN/pre-load.ll b/test/Transforms/GVN/pre-load.ll
index 637a6d26c8..3cb67135ac 100644
--- a/test/Transforms/GVN/pre-load.ll
+++ b/test/Transforms/GVN/pre-load.ll
@@ -22,6 +22,7 @@ block4:
 ; CHECK-NEXT: ret i32
 }
 
+; This is a simple phi translation case.
 define i32 @test2(i32* %p, i32* %q, i1 %C) {
 ; CHECK: @test2
 block1:
@@ -46,6 +47,7 @@ block4:
 ; CHECK: ret i32
 }
 
+; This is a PRE case that requires phi translation through a GEP.
 define i32 @test3(i32* %p, i32* %q, i32** %Hack, i1 %C) {
 ; CHECK: @test3
 block1:
@@ -73,3 +75,35 @@ block4:
 ; CHECK-NOT: load
 ; CHECK: ret i32
 }
+
+;; Here the loaded address is available, but the computation is in 'block3'
+;; which does not dominate 'block2'.
+define i32 @test4(i32* %p, i32* %q, i32** %Hack, i1 %C) {
+; CHECK: @test4
+block1:
+	br i1 %C, label %block2, label %block3
+
+block2:
+ br label %block4
+; CHECK: block2:
+; CHECK:   load i32*
+; CHECK:   br label %block4
+
+block3:
+  %B = getelementptr i32* %q, i32 1
+  store i32* %B, i32** %Hack
+
+  %A = getelementptr i32* %p, i32 1
+  store i32 0, i32* %A
+  br label %block4
+
+block4:
+  %P2 = phi i32* [%p, %block3], [%q, %block2]
+  %P3 = getelementptr i32* %P2, i32 1
+  %PRE = load i32* %P3
+  ret i32 %PRE
+; CHECK: block4:
+; CHECK-NEXT: phi i32 [
+; CHECK-NOT: load
+; CHECK: ret i32
+}