[SimplifyCFG] Tail-merge calls with sideeffects

This was deliberately disabled during my rewrite of SinkIfThenToEnd to keep behaviour
at least vaguely consistent with the previous version and keep it as close to NFC as
I could.

There's no real reason not to merge sideeffect calls though, so let's do it! Small fixup
along the way to ensure we don't create indirect calls.

Should fix PR28964.

llvm-svn: 280215

2 files changed, 27 insertions, 8 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 2868641..dc36a6e 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -1433,11 +1433,6 @@ static bool canSinkLastInstruction(ArrayRef<BasicBlock*> Blocks,
     if (isa<PHINode>(I) || I->isEHPad() || isa<AllocaInst>(I) ||
         I->getType()->isTokenTy())
       return false;
-    // Apart from loads and stores, we won't move anything that could
-    // change memory or have sideeffects.
-    if (!isa<StoreInst>(I) && !isa<LoadInst>(I) &&
-        (I->mayHaveSideEffects() || I->mayHaveSideEffects()))
-      return false;
     // Everything must have only one use too, apart from stores which
     // have no uses.
     if (!isa<StoreInst>(I) && !I->hasOneUse())
@@ -1472,10 +1467,11 @@ static bool canSinkLastInstruction(ArrayRef<BasicBlock*> Blocks,
       if (!canReplaceOperandWithVariable(I0, OI))
         // We can't create a PHI from this GEP.
         return false;
-      if ((isa<CallInst>(I0) || isa<InvokeInst>(I0)) && OI != 0)
-        // Don't create indirect calls!
+      // Don't create indirect calls! The called value is the final operand.
+      if ((isa<CallInst>(I0) || isa<InvokeInst>(I0)) && OI == OE - 1) {
         // FIXME: if the call was *already* indirect, we should do this.
         return false;
+      }
       ++NumPHIsRequired;
     }
   }
diff --git a/llvm/test/Transforms/SimplifyCFG/sink-common-code.ll b/llvm/test/Transforms/SimplifyCFG/sink-common-code.ll
index e3a86dc..fe501b9 100644
--- a/llvm/test/Transforms/SimplifyCFG/sink-common-code.ll
+++ b/llvm/test/Transforms/SimplifyCFG/sink-common-code.ll
@@ -344,6 +344,29 @@ if.end:
 ; CHECK-NOT: load
 ; CHECK-NOT: store
 
+; The call should be commoned.
+define i32 @test13a(i1 zeroext %flag, i32 %w, i32 %x, i32 %y) {
+entry:
+  br i1 %flag, label %if.then, label %if.else
+
+if.then:
+  %sv1 = call i32 @bar(i32 %x)
+  br label %if.end
+
+if.else:
+  %sv2 = call i32 @bar(i32 %y)
+  br label %if.end
+
+if.end:
+  %p = phi i32 [ %sv1, %if.then ], [ %sv2, %if.else ]
+  ret i32 1
+}
+declare i32 @bar(i32)
+
+; CHECK-LABEL: test13a
+; CHECK: %[[x:.*]] = select i1 %flag
+; CHECK: call i32 @bar(i32 %[[x]])
+
 ; CHECK: !0 = !{!1, !1, i64 0}
 ; CHECK: !1 = !{!"float", !2}
-; CHECK: !2 = !{!"an example type tree"}
\ No newline at end of file
+; CHECK: !2 = !{!"an example type tree"}