[SimplifyCFG] Rewrite SinkThenElseCodeToEnd

The new version has several advantages:
  1) IMSHO it's more readable and neater
  2) It handles loads and stores properly
  3) It can handle any number of incoming blocks rather than just two. I'll be taking advantage of this in a followup patch.

With this change we can now finally sink load-modify-store idioms such as:

    if (a)
      return *b += 3;
    else
      return *b += 4;

    =>

    %z = load i32, i32* %y
    %.sink = select i1 %a, i32 5, i32 7
    %b = add i32 %z, %.sink
    store i32 %b, i32* %y
    ret i32 %b

When this works for switches it'll be even more powerful.

llvm-svn: 278660

1 files changed, 177 insertions, 0 deletions

diff --git a/llvm/test/Transforms/SimplifyCFG/sink-common-code.ll b/llvm/test/Transforms/SimplifyCFG/sink-common-code.ll
index cdb6ed29d85..4277ae0e33a 100644
--- a/llvm/test/Transforms/SimplifyCFG/sink-common-code.ll
+++ b/llvm/test/Transforms/SimplifyCFG/sink-common-code.ll
@@ -81,3 +81,180 @@ if.end:
 ; CHECK: call
 ; CHECK: add
 ; CHECK-NOT: br
+
+define i32 @test4(i1 zeroext %flag, i32 %x, i32* %y) {
+entry:
+  br i1 %flag, label %if.then, label %if.else
+
+if.then:
+  %a = add i32 %x, 5
+  store i32 %a, i32* %y
+  br label %if.end
+
+if.else:
+  %b = add i32 %x, 7
+  store i32 %b, i32* %y
+  br label %if.end
+
+if.end:
+  ret i32 1
+}
+
+; CHECK-LABEL: test4
+; CHECK: select
+; CHECK: store
+; CHECK-NOT: store
+
+define i32 @test5(i1 zeroext %flag, i32 %x, i32* %y) {
+entry:
+  br i1 %flag, label %if.then, label %if.else
+
+if.then:
+  %a = add i32 %x, 5
+  store volatile i32 %a, i32* %y
+  br label %if.end
+
+if.else:
+  %b = add i32 %x, 7
+  store i32 %b, i32* %y
+  br label %if.end
+
+if.end:
+  ret i32 1
+}
+
+; CHECK-LABEL: test5
+; CHECK: store volatile
+; CHECK: store
+
+define i32 @test6(i1 zeroext %flag, i32 %x, i32* %y) {
+entry:
+  br i1 %flag, label %if.then, label %if.else
+
+if.then:
+  %a = add i32 %x, 5
+  store volatile i32 %a, i32* %y
+  br label %if.end
+
+if.else:
+  %b = add i32 %x, 7
+  store volatile i32 %b, i32* %y
+  br label %if.end
+
+if.end:
+  ret i32 1
+}
+
+; CHECK-LABEL: test6
+; CHECK: select
+; CHECK: store volatile
+; CHECK-NOT: store
+
+define i32 @test7(i1 zeroext %flag, i32 %x, i32* %y) {
+entry:
+  br i1 %flag, label %if.then, label %if.else
+
+if.then:
+  %z = load volatile i32, i32* %y
+  %a = add i32 %z, 5
+  store volatile i32 %a, i32* %y
+  br label %if.end
+
+if.else:
+  %w = load volatile i32, i32* %y
+  %b = add i32 %w, 7
+  store volatile i32 %b, i32* %y
+  br label %if.end
+
+if.end:
+  ret i32 1
+}
+
+; CHECK-LABEL: test7
+; CHECK-DAG: select
+; CHECK-DAG: load volatile
+; CHECK: store volatile
+; CHECK-NOT: load
+; CHECK-NOT: store
+
+; %z and %w are in different blocks. We shouldn't sink the add because
+; there may be intervening memory instructions.
+define i32 @test8(i1 zeroext %flag, i32 %x, i32* %y) {
+entry:
+  %z = load volatile i32, i32* %y
+  br i1 %flag, label %if.then, label %if.else
+
+if.then:
+  %a = add i32 %z, 5
+  store volatile i32 %a, i32* %y
+  br label %if.end
+
+if.else:
+  %w = load volatile i32, i32* %y
+  %b = add i32 %w, 7
+  store volatile i32 %b, i32* %y
+  br label %if.end
+
+if.end:
+  ret i32 1
+}
+
+; CHECK-LABEL: test8
+; CHECK: add
+; CHECK: add
+
+; The extra store in %if.then means %z and %w are not equivalent.
+define i32 @test9(i1 zeroext %flag, i32 %x, i32* %y, i32* %p) {
+entry:
+  br i1 %flag, label %if.then, label %if.else
+
+if.then:
+  store i32 7, i32* %p
+  %z = load volatile i32, i32* %y
+  store i32 6, i32* %p
+  %a = add i32 %z, 5
+  store volatile i32 %a, i32* %y
+  br label %if.end
+
+if.else:
+  %w = load volatile i32, i32* %y
+  %b = add i32 %w, 7
+  store volatile i32 %b, i32* %y
+  br label %if.end
+
+if.end:
+  ret i32 1
+}
+
+; CHECK-LABEL: test9
+; CHECK: add
+; CHECK: add
+
+%struct.anon = type { i32, i32 }
+
+; The GEP indexes a struct type so cannot have a variable last index.
+define i32 @test10(i1 zeroext %flag, i32 %x, i32* %y, %struct.anon* %s) {
+entry:
+  br i1 %flag, label %if.then, label %if.else
+
+if.then:
+  %dummy = add i32 %x, 5
+  %gepa = getelementptr inbounds %struct.anon, %struct.anon* %s, i32 0, i32 0
+  store volatile i32 %x, i32* %gepa
+  br label %if.end
+
+if.else:
+  %dummy1 = add i32 %x, 6
+  %gepb = getelementptr inbounds %struct.anon, %struct.anon* %s, i32 0, i32 1
+  store volatile i32 %x, i32* %gepb
+  br label %if.end
+
+if.end:
+  ret i32 1
+}
+
+; CHECK-LABEL: test10
+; CHECK: getelementptr
+; CHECK: getelementptr
+; CHECK: phi
+; CHECK: store volatile