From 19236d53eb6f4ee4538ac12efcd77000b2f7ae78 Mon Sep 17 00:00:00 2001 From: Hans Wennborg Date: Sun, 12 Jan 2014 00:44:41 +0000 Subject: Switch-to-lookup tables: Don't require a result for the default case when the lookup table doesn't have any holes. This means we can build a lookup table for switches like this: switch (x) { case 0: return 1; case 1: return 2; case 2: return 3; case 3: return 4; default: exit(1); } The default case doesn't yield a constant result here, but that doesn't matter, since a default result is only necessary for filling holes in the lookup table, and this table doesn't have any holes. This makes us transform 505 more switches in a clang bootstrap, and shaves 164 KB off the resulting clang binary. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199025 91177308-0d34-0410-b5e6-96231b3b80d8 --- .../SimplifyCFG/X86/switch_to_lookup_table.ll | 50 ++++++++++++++++++++++ 1 file changed, 50 insertions(+) (limited to 'test/Transforms/SimplifyCFG') diff --git a/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll b/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll index 368732711a..4ac02dbdf3 100644 --- a/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll +++ b/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll @@ -806,3 +806,53 @@ return: ; CHECK-NOT: @switch.table ; CHECK: switch i32 %c } + +; If we can build a lookup table without any holes, we don't need a default result. +declare void @exit(i32) +define i32 @nodefaultnoholes(i32 %c) { +entry: + switch i32 %c, label %sw.default [ + i32 0, label %return + i32 1, label %sw.bb1 + i32 2, label %sw.bb2 + i32 3, label %sw.bb3 + ] + +sw.bb1: br label %return +sw.bb2: br label %return +sw.bb3: br label %return +sw.default: call void @exit(i32 1) + unreachable +return: + %x = phi i32 [ -1, %sw.bb3 ], [ 0, %sw.bb2 ], [ 123, %sw.bb1 ], [ 55, %entry ] + ret i32 %x + +; CHECK-LABEL: @nodefaultnoholes( +; CHECK: @switch.table +; CHECK-NOT: switch i32 +} + +; This lookup table will have holes, so we cannot build it without default result. +define i32 @nodefaultwithholes(i32 %c) { +entry: + switch i32 %c, label %sw.default [ + i32 0, label %return + i32 1, label %sw.bb1 + i32 2, label %sw.bb2 + i32 3, label %sw.bb3 + i32 5, label %sw.bb3 + ] + +sw.bb1: br label %return +sw.bb2: br label %return +sw.bb3: br label %return +sw.default: call void @exit(i32 1) + unreachable +return: + %x = phi i32 [ -1, %sw.bb3 ], [ 0, %sw.bb2 ], [ 123, %sw.bb1 ], [ 55, %entry ] + ret i32 %x + +; CHECK-LABEL: @nodefaultwithholes( +; CHECK-NOT: @switch.table +; CHECK: switch i32 +} -- cgit v1.2.3