GVN does simple propagation of conditions: when it sees a conditional

branch "br i1 %x, label %if_true, label %if_false" then it replaces
"%x" with "true" in places only reachable via the %if_true arm, and
with "false" in places only reachable via the %if_false arm.  Except
that actually it doesn't: if value numbering shows that %y is equal
to %x then, yes, %y will be turned into true/false in this way, but
any occurrences of %x itself are not transformed.  Fix this.  What's
more, it's often the case that %x is an equality comparison such as
"%x = icmp eq %A, 0", in which case every occurrence of %A that is
only reachable via the %if_true arm can be replaced with 0.  Implement
this and a few other variations on this theme.  This reduces the number
of lines of LLVM IR in "GCC as one big file" by 0.2%.  It has a bigger
impact on Ada code, typically reducing the number of lines of bitcode
by around 0.4% by removing repeated compiler generated checks.  Passes
the LLVM nightly testsuite and the Ada ACATS testsuite.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@141177 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 34 insertions, 10 deletions

diff --git a/test/Transforms/GVN/condprop.ll b/test/Transforms/GVN/condprop.ll
index b0728565f3..705490b67f 100644
--- a/test/Transforms/GVN/condprop.ll
+++ b/test/Transforms/GVN/condprop.ll
@@ -2,8 +2,8 @@
 
 @a = external global i32		; <i32*> [#uses=7]
 
-; CHECK: @foo
-define i32 @foo() nounwind {
+; CHECK: @test1
+define i32 @test1() nounwind {
 entry:
 	%0 = load i32* @a, align 4
 	%1 = icmp eq i32 %0, 4
@@ -54,22 +54,46 @@ return:		; preds = %bb8
 	ret i32 %.0
 }
 
-declare void @ext(i1)
+declare void @foo(i1)
 
-; CHECK: @bar
-define void @bar(i1 %x, i1 %y) {
+; CHECK: @test2
+define void @test2(i1 %x, i1 %y) {
   %z = or i1 %x, %y
   br i1 %z, label %true, label %false
 true:
 ; CHECK: true:
   %z2 = or i1 %x, %y
-  call void @ext(i1 %z2)
-; CHECK: call void @ext(i1 true)
+  call void @foo(i1 %z2)
+; CHECK: call void @foo(i1 true)
   br label %true
 false:
 ; CHECK: false:
   %z3 = or i1 %x, %y
-  call void @ext(i1 %z3)
-; CHECK: call void @ext(i1 false)
+  call void @foo(i1 %z3)
+; CHECK: call void @foo(i1 false)
   br label %false
 }
+
+declare void @bar(i32)
+
+; CHECK: @test3
+define void @test3(i32 %x, i32 %y) {
+  %xz = icmp eq i32 %x, 0
+  %yz = icmp eq i32 %y, 0
+  %z = and i1 %xz, %yz
+  br i1 %z, label %both_zero, label %nope
+both_zero:
+  call void @foo(i1 %xz)
+; CHECK: call void @foo(i1 true)
+  call void @foo(i1 %yz)
+; CHECK: call void @foo(i1 true)
+  call void @bar(i32 %x)
+; CHECK: call void @bar(i32 0)
+  call void @bar(i32 %y)
+; CHECK: call void @bar(i32 0)
+  ret void
+nope:
+  call void @foo(i1 %z)
+; CHECK: call void @foo(i1 false)
+  ret void
+}
diff --git a/test/Transforms/GVN/phi-translate.ll b/test/Transforms/GVN/phi-translate.ll
index f10537e0c9..fa91d2919e 100644
--- a/test/Transforms/GVN/phi-translate.ll
+++ b/test/Transforms/GVN/phi-translate.ll
@@ -14,7 +14,7 @@ target datalayout = "e-p:64:64:64"
 @G = external global [100 x i32]
 define i32 @foo(i32 %x, i32 %z) {
 entry:
-  %tobool = icmp eq i32 %x, 0
+  %tobool = icmp eq i32 %z, 0
   br i1 %tobool, label %end, label %then
 
 then: