From 1f17c2f83a02bab1beb2f598f9f6a80dff80313c Mon Sep 17 00:00:00 2001
From: James Molloy <james.molloy@arm.com>
Date: Mon, 19 Sep 2016 08:23:08 +0000
Subject: [PATCH] [SimplifyCFG] Update (AND) IR flags when CSE'ing instructions

We were updating metadata but not IR flags. Because we pick an arbitrary instruction to be the CSE candidate, it comes down to luck (50% or less chance) if this results in broken codegen or not, which is why PR30373 which is actually not the fault of the commit it was bisected down to.

Fixes PR30373.

llvm-svn: 281889
---
 lib/Transforms/Utils/SimplifyCFG.cpp          |  6 +-
 .../SimplifyCFG/sink-common-code.ll           | 56 +++++++++++++++++++
 2 files changed, 60 insertions(+), 2 deletions(-)

diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index 877e55928d4..90ce6720182 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -1527,10 +1527,12 @@ static bool sinkLastInstruction(ArrayRef<BasicBlock*> Blocks) {
     I0->getOperandUse(O).set(NewOperands[O]);
   I0->moveBefore(&*BBEnd->getFirstInsertionPt());
 
-  // Update metadata.
+  // Update metadata and IR flags.
   for (auto *I : Insts)
-    if (I != I0)
+    if (I != I0) {
       combineMetadataForCSE(I0, I);
+      I0->andIRFlags(I);
+    }
 
   if (!isa<StoreInst>(I0)) {
     // canSinkLastInstruction checked that all instructions were used by
diff --git a/test/Transforms/SimplifyCFG/sink-common-code.ll b/test/Transforms/SimplifyCFG/sink-common-code.ll
index e944a9bc1e9..54f87052c7a 100644
--- a/test/Transforms/SimplifyCFG/sink-common-code.ll
+++ b/test/Transforms/SimplifyCFG/sink-common-code.ll
@@ -699,6 +699,62 @@ if.end:
 ; CHECK: store
 ; CHECK: store
 
+define i32 @test_pr30373a(i1 zeroext %flag, i32 %x, i32 %y) {
+entry:
+  br i1 %flag, label %if.then, label %if.else
+
+if.then:
+  %x0 = call i32 @foo(i32 %x, i32 0) nounwind readnone
+  %y0 = call i32 @foo(i32 %x, i32 1) nounwind readnone
+  %z0 = lshr i32 %y0, 8
+  br label %if.end
+
+if.else:
+  %x1 = call i32 @foo(i32 %y, i32 0) nounwind readnone
+  %y1 = call i32 @foo(i32 %y, i32 1) nounwind readnone
+  %z1 = lshr exact i32 %y1, 8
+  br label %if.end
+
+if.end:
+  %xx = phi i32 [ %x0, %if.then ], [ %x1, %if.else ]
+  %yy = phi i32 [ %z0, %if.then ], [ %z1, %if.else ]
+  %ret = add i32 %xx, %yy
+  ret i32 %ret
+}
+
+; CHECK-LABEL: test_pr30373a
+; CHECK: lshr
+; CHECK-NOT: exact
+; CHECK: }
+
+define i32 @test_pr30373b(i1 zeroext %flag, i32 %x, i32 %y) {
+entry:
+  br i1 %flag, label %if.then, label %if.else
+
+if.then:
+  %x0 = call i32 @foo(i32 %x, i32 0) nounwind readnone
+  %y0 = call i32 @foo(i32 %x, i32 1) nounwind readnone
+  %z0 = lshr exact i32 %y0, 8
+  br label %if.end
+
+if.else:
+  %x1 = call i32 @foo(i32 %y, i32 0) nounwind readnone
+  %y1 = call i32 @foo(i32 %y, i32 1) nounwind readnone
+  %z1 = lshr i32 %y1, 8
+  br label %if.end
+
+if.end:
+  %xx = phi i32 [ %x0, %if.then ], [ %x1, %if.else ]
+  %yy = phi i32 [ %z0, %if.then ], [ %z1, %if.else ]
+  %ret = add i32 %xx, %yy
+  ret i32 %ret
+}
+
+; CHECK-LABEL: test_pr30373b
+; CHECK: lshr
+; CHECK-NOT: exact
+; CHECK: }
+
 ; CHECK: !0 = !{!1, !1, i64 0}
 ; CHECK: !1 = !{!"float", !2}
 ; CHECK: !2 = !{!"an example type tree"}