[SimpleLoopUnswitch] partial unswitch needs to be careful when replac…

…ing invariants with constants When partial unswitch operates on multiple conditions at once, .e.g: if (Cond1 || Cond2 || NonInv) ... it should infer (and replace) values for individual conditions only on one side of unswitch and not another. More precisely only these derivations hold true: (Cond1 || Cond2) == false => Cond1 == Cond2 == false (Cond1 && Cond2) == true => Cond1 == Cond2 == true By the way we organize unswitching it means only replacing on "continue" blocks and never on "unswitched" ones. Since trivial unswitch does not have "unswitched" blocks it does not have this problem. Fixes PR 39568. Reviewers: chandlerc, asbirlea Differential Revision: https://reviews.llvm.org/D54211 llvm-svn: 346350
llvm · Nov 7, 2018 · f9a02a7 · f9a02a7
1 parent df5b09b
commit f9a02a7
Showing 2 changed files with 112 additions and 12 deletions.
diff --git a/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp b/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
@@ -2044,6 +2044,18 @@ static void unswitchNontrivialInvariants(
     assert(UnswitchedSuccBBs.size() == 1 &&
            "Only one possible unswitched block for a branch!");
     BasicBlock *ClonedPH = ClonedPHs.begin()->second;
+
+    // When considering multiple partially-unswitched invariants
+    // we cant just go replace them with constants in both branches.
+    //
+    // For 'AND' we infer that true branch ("continue") means true
+    // for each invariant operand.
+    // For 'OR' we can infer that false branch ("continue") means false
+    // for each invariant operand.
+    // So it happens that for multiple-partial case we dont replace
+    // in the unswitched branch.
+    bool ReplaceUnswitched = FullUnswitch || (Invariants.size() == 1);
+
     ConstantInt *UnswitchedReplacement =
         Direction ? ConstantInt::getTrue(BI->getContext())
                   : ConstantInt::getFalse(BI->getContext());
@@ -2063,7 +2075,8 @@ static void unswitchNontrivialInvariants(
         // unswitched if in the cloned blocks.
         if (DT.dominates(LoopPH, UserI->getParent()))
           U->set(ContinueReplacement);
-        else if (DT.dominates(ClonedPH, UserI->getParent()))
+        else if (ReplaceUnswitched &&
+                 DT.dominates(ClonedPH, UserI->getParent()))
           U->set(UnswitchedReplacement);
       }
   }

diff --git a/llvm/test/Transforms/SimpleLoopUnswitch/nontrivial-unswitch.ll b/llvm/test/Transforms/SimpleLoopUnswitch/nontrivial-unswitch.ll
@@ -2796,10 +2796,10 @@ loop_begin:
 ; CHECK:       loop_begin.us:
 ; CHECK-NEXT:    %[[V1_US:.*]] = load i1, i1* %ptr1
 ; CHECK-NEXT:    %[[V2_US:.*]] = load i1, i1* %ptr2
-; CHECK-NEXT:    %[[AND1_US:.*]] = and i1 %[[V1_US]], false
+; CHECK-NEXT:    %[[AND1_US:.*]] = and i1 %[[V1_US]], %cond1
 ; CHECK-NEXT:    %[[OR1_US:.*]] = or i1 %[[V2_US]], %cond2
 ; CHECK-NEXT:    %[[AND2_US:.*]] = and i1 %[[AND1_US]], %[[OR1_US]]
-; CHECK-NEXT:    %[[AND3_US:.*]] = and i1 %[[AND2_US]], false
+; CHECK-NEXT:    %[[AND3_US:.*]] = and i1 %[[AND2_US]], %cond3
 ; CHECK-NEXT:    br label %loop_b.us
 ;
 ; CHECK:       loop_b.us:
@@ -2857,12 +2857,99 @@ loop_exit:
 ; CHECK-NEXT:    ret
 }
 
-; Non-trivial unswitching of a switch.
-define i32 @test27(i1* %ptr, i32 %cond) {
+; Non-trivial partial loop unswitching of multiple invariant inputs to an `or`
+; chain. Basically an inverted version of corresponding `and` test (test26).
+define i32 @test27(i1* %ptr1, i1* %ptr2, i1* %ptr3, i1 %cond1, i1 %cond2, i1 %cond3) {
 ; CHECK-LABEL: @test27(
 entry:
   br label %loop_begin
 ; CHECK-NEXT:  entry:
+; CHECK-NEXT:    %[[INV_OR:.*]] = or i1 %cond3, %cond1
+; CHECK-NEXT:    br i1 %[[INV_OR]], label %entry.split.us, label %entry.split
+
+loop_begin:
+  %v1 = load i1, i1* %ptr1
+  %v2 = load i1, i1* %ptr2
+  %cond_or1 = or i1 %v1, %cond1
+  %cond_and1 = and i1 %v2, %cond2
+  %cond_or2 = or i1 %cond_or1, %cond_and1
+  %cond_or3 = or i1 %cond_or2, %cond3
+  br i1 %cond_or3, label %loop_b, label %loop_a
+; The 'loop_b' unswitched loop.
+;
+; CHECK:       entry.split.us:
+; CHECK-NEXT:    br label %loop_begin.us
+;
+; CHECK:       loop_begin.us:
+; CHECK-NEXT:    %[[V1_US:.*]] = load i1, i1* %ptr1
+; CHECK-NEXT:    %[[V2_US:.*]] = load i1, i1* %ptr2
+; CHECK-NEXT:    %[[OR1_US:.*]] = or i1 %[[V1_US]], %cond1
+; CHECK-NEXT:    %[[AND1_US:.*]] = and i1 %[[V2_US]], %cond2
+; CHECK-NEXT:    %[[OR2_US:.*]] = or i1 %[[OR1_US]], %[[AND1_US]]
+; CHECK-NEXT:    %[[OR3_US:.*]] = or i1 %[[OR2_US]], %cond3
+; CHECK-NEXT:    br label %loop_b.us
+;
+; CHECK:       loop_b.us:
+; CHECK-NEXT:    call i32 @b()
+; CHECK-NEXT:    br label %latch.us
+;
+; CHECK:       latch.us:
+; CHECK-NEXT:    %[[V3_US:.*]] = load i1, i1* %ptr3
+; CHECK-NEXT:    br i1 %[[V3_US]], label %loop_begin.us, label %loop_exit.split.us
+;
+; CHECK:       loop_exit.split.us:
+; CHECK-NEXT:    br label %loop_exit
+
+; The original loop.
+;
+; CHECK:       entry.split:
+; CHECK-NEXT:    br label %loop_begin
+;
+; CHECK:       loop_begin:
+; CHECK-NEXT:    %[[V1:.*]] = load i1, i1* %ptr1
+; CHECK-NEXT:    %[[V2:.*]] = load i1, i1* %ptr2
+; CHECK-NEXT:    %[[OR1:.*]] = or i1 %[[V1]], false
+; CHECK-NEXT:    %[[AND1:.*]] = and i1 %[[V2]], %cond2
+; CHECK-NEXT:    %[[OR2:.*]] = or i1 %[[OR1]], %[[AND1]]
+; CHECK-NEXT:    %[[OR3:.*]] = or i1 %[[OR2]], false
+; CHECK-NEXT:    br i1 %[[OR3]], label %loop_b, label %loop_a
+
+loop_a:
+  call i32 @a()
+  br label %latch
+; CHECK:       loop_a:
+; CHECK-NEXT:    call i32 @a()
+; CHECK-NEXT:    br label %latch
+
+loop_b:
+  call i32 @b()
+  br label %latch
+; CHECK:       loop_b:
+; CHECK-NEXT:    call i32 @b()
+; CHECK-NEXT:    br label %latch
+
+latch:
+  %v3 = load i1, i1* %ptr3
+  br i1 %v3, label %loop_begin, label %loop_exit
+; CHECK:       latch:
+; CHECK-NEXT:    %[[V3:.*]] = load i1, i1* %ptr3
+; CHECK-NEXT:    br i1 %[[V3]], label %loop_begin, label %loop_exit.split
+
+loop_exit:
+  ret i32 0
+; CHECK:       loop_exit.split:
+; CHECK-NEXT:    br label %loop_exit
+;
+; CHECK:       loop_exit:
+; CHECK-NEXT:    ret
+}
+
+; Non-trivial unswitching of a switch.
+define i32 @test28(i1* %ptr, i32 %cond) {
+; CHECK-LABEL: @test28(
+entry:
+  br label %loop_begin
+; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    switch i32 %cond, label %[[ENTRY_SPLIT_LATCH:.*]] [
 ; CHECK-NEXT:      i32 0, label %[[ENTRY_SPLIT_A:.*]]
 ; CHECK-NEXT:      i32 1, label %[[ENTRY_SPLIT_B:.*]]
@@ -2970,8 +3057,8 @@ loop_exit:
 ; can introduce multiple edges to successors. These need lots of special case
 ; handling as they get collapsed in many cases (domtree, the unswitch itself)
 ; but not in all cases (the PHI node operands).
-define i32 @test28(i32 %arg) {
-; CHECK-LABEL: @test28(
+define i32 @test29(i32 %arg) {
+; CHECK-LABEL: @test29(
 entry:
   br label %header
 ; CHECK-NEXT:  entry:
@@ -3149,12 +3236,12 @@ exit:
 ; CHECK-NEXT:    ret i32 %[[EXIT_PHI2]]
 }
 
-; Similar to @test28 but designed to have one of the duplicate edges be
+; Similar to @test29 but designed to have one of the duplicate edges be
 ; a loop exit edge as those can in some cases be special. Among other things,
 ; this includes an LCSSA phi with multiple entries despite being a dedicated
 ; exit block.
-define i32 @test29(i32 %arg) {
-; CHECK-LABEL: define i32 @test29(
+define i32 @test30(i32 %arg) {
+; CHECK-LABEL: define i32 @test30(
 entry:
   br label %header
 ; CHECK-NEXT:  entry:
@@ -3946,8 +4033,8 @@ exit:
 ; viable for unswitching the inner-most loop. This lets us check that the
 ; unswitching doesn't end up cycling infinitely even when the cycle is
 ; indirect and due to revisiting a loop after cloning.
-define void @test30(i32 %arg) {
-; CHECK-LABEL: define void @test30(
+define void @test31(i32 %arg) {
+; CHECK-LABEL: define void @test31(
 entry:
   br label %outer.header
 ; CHECK-NEXT:  entry: