From 49cad7d70b663a1f258c40cbc94deb01cd4ba5df Mon Sep 17 00:00:00 2001
From: George Burgess IV <george.burgess.iv@gmail.com>
Date: Wed, 30 Mar 2016 03:12:08 +0000
Subject: [MemorySSA] Make the visitor more careful with calls.

Prior to this patch, the MemorySSA caching visitor would cache all
calls that it visited. When paired with phi optimization, this can be
problematic. Consider:

define void @foo() {
  ; 1 = MemoryDef(liveOnEntry)
  call void @clobberFunction()
  br i1 undef, label %if.end, label %if.then

if.then:
  ; MemoryUse(??)
  call void @readOnlyFunction()
  ; 2 = MemoryDef(1)
  call void @clobberFunction()
  br label %if.end

if.end:
  ; 3 = MemoryPhi(...)
  ; MemoryUse(?)
  call void @readOnlyFunction()
  ret void
}

When optimizing MemoryUse(?), we visit defs 1 and 2, so we note to
cache them later. We ultimately end up not being able to optimize
passed the Phi, so we set MemoryUse(?) to point to the Phi. We then
cache the clobbering call for def 1 to be the Phi.

This commit changes this behavior so that we wipe out any calls
added to VisistedCalls while visiting the defs of a phi we couldn't
optimize.

Aside: With this patch, we now can bootstrap clang/LLVM without a
single MemorySSA verifier failure. Woohoo. :)

llvm-svn: 264820
---
 .../Transforms/Util/MemorySSA/function-clobber.ll  | 27 ++++++++++++++++++++++
 1 file changed, 27 insertions(+)

(limited to 'llvm/test/Transforms/Util')

diff --git a/llvm/test/Transforms/Util/MemorySSA/function-clobber.ll b/llvm/test/Transforms/Util/MemorySSA/function-clobber.ll
index 97e231a4ea2..937ab245191 100644
--- a/llvm/test/Transforms/Util/MemorySSA/function-clobber.ll
+++ b/llvm/test/Transforms/Util/MemorySSA/function-clobber.ll
@@ -24,3 +24,30 @@ define i32 @foo() {
   %3 = add i32 %2, %1
   ret i32 %3
 }
+
+declare void @readEverything() readonly
+declare void @clobberEverything()
+
+; CHECK-LABEL: define void @bar
+define void @bar() {
+; CHECK: 1 = MemoryDef(liveOnEntry)
+; CHECK-NEXT: call void @clobberEverything()
+  call void @clobberEverything()
+  br i1 undef, label %if.end, label %if.then
+
+if.then:
+; CHECK: MemoryUse(1)
+; CHECK-NEXT: call void @readEverything()
+  call void @readEverything()
+; CHECK: 2 = MemoryDef(1)
+; CHECK-NEXT: call void @clobberEverything()
+  call void @clobberEverything()
+  br label %if.end
+
+if.end:
+; CHECK: 3 = MemoryPhi({%0,1},{if.then,2})
+; CHECK: MemoryUse(3)
+; CHECK-NEXT: call void @readEverything()
+  call void @readEverything()
+  ret void
+}
-- 
cgit v1.2.3