add a note, progress unblocked by PR8575 being fixed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@124599 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/README.txt b/lib/Target/README.txt
index c0a2b760de78955f01fa24dcf905f014f78ceb76..b3bc7498566f4add6789eeac727289d354d837b9 100644 (file)
--- a/lib/Target/README.txt
+++ b/lib/Target/README.txt
@@ -2274,3 +2274,51 @@ llc time when it gets inlined, because we can use smaller transfers.  This also
 avoids partial register stalls in some important cases.
 
 //===---------------------------------------------------------------------===//
+
+With PR8575 we're now generating better code for:
+
+static _Bool foo(int x) { return x == 1; }
+static _Bool bar(int x) { return x == 2; }
+static _Bool baz(int x) { return x == 3; }
+
+_Bool quux(int x) {
+ return foo(x) || bar(x) || baz(x);
+}
+
+$ clang t.c -S -o - -O3 -mkernel -fomit-frame-pointer 
+_quux:                                  ## @quux
+## BB#0:                                ## %entry
+       decl    %edi
+       cmpl    $3, %edi
+       movb    $1, %al
+       jb      LBB0_2
+## BB#1:                                ## %lor.rhs
+       xorb    %al, %al
+LBB0_2:                                 ## %lor.end
+       movzbl  %al, %eax
+       andl    $1, %eax
+       ret
+
+But this should use a "setcc" instead of materializing a 0/1 value
+the hard way.  This looks like #1: simplifycfg should transform the
+switch into a sub+icmp+branch, and an instcombine hack to replace 
+the PHI with a zext of the branch condition.  Here's the IR today:
+
+define zeroext i1 @quux(i32 %x) nounwind readnone ssp noredzone {
+entry:
+  switch i32 %x, label %lor.rhs [
+    i32 1, label %lor.end
+    i32 2, label %lor.end
+    i32 3, label %lor.end
+  ]
+
+lor.rhs:                                          ; preds = %entry
+  br label %lor.end
+
+lor.end:                                          ; preds = %lor.rhs, %entry, %entry, %entry
+  %0 = phi i1 [ true, %entry ], [ false, %lor.rhs ], [ true, %entry ], [ true, %entry ]
+  ret i1 %0
+}
+
+//===---------------------------------------------------------------------===//
+