[llvm] 181628b - [SimpleLoopUnswitch] Fix introduction of UB when hoisted condition may be undef or poison

Juneyoung Lee via llvm-commits llvm-commits at lists.llvm.org
Tue Feb 25 20:47:41 PST 2020


Author: Juneyoung Lee
Date: 2020-02-26T13:47:33+09:00
New Revision: 181628b52d390f2136fb5a63fe644d230a9b822d

URL: https://github.com/llvm/llvm-project/commit/181628b52d390f2136fb5a63fe644d230a9b822d
DIFF: https://github.com/llvm/llvm-project/commit/181628b52d390f2136fb5a63fe644d230a9b822d.diff

LOG: [SimpleLoopUnswitch] Fix introduction of UB when hoisted condition may be undef or poison

Summary:
Loop unswitch hoists branches on loop-invariant conditions. However, if this
condition is poison/undef and the branch wasn't originally reachable, loop
unswitch introduces UB (since the optimized code will branch on poison/undef and
the original one didn't)).
We fix this problem by freezing the condition to ensure we don't introduce UB.

We will now transform the following:
  while (...) {
    if (C) { A }
    else   { B }
  }

Into:
  C' = freeze(C)
  if (C') {
    while (...) { A }
  } else {
    while (...) { B }
  }

This patch fixes the root cause of the following bug reports (which use the old loop unswitch, but can be reproduced with minor changes in the code and -enable-nontrivial-unswitch):
- https://llvm.org/bugs/show_bug.cgi?id=27506
- https://llvm.org/bugs/show_bug.cgi?id=31652

Reviewers: reames, majnemer, chenli, sanjoy, hfinkel

Reviewed By: reames

Subscribers: hiraditya, jvesely, nhaehnle, filcab, regehr, trentxintong, nlopes, llvm-commits, mzolotukhin

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D29015

Added: 
    

Modified: 
    llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
    llvm/test/Transforms/SimpleLoopUnswitch/exponential-nontrivial-unswitch-nested.ll
    llvm/test/Transforms/SimpleLoopUnswitch/exponential-nontrivial-unswitch-nested2.ll
    llvm/test/Transforms/SimpleLoopUnswitch/exponential-switch-unswitch.ll
    llvm/test/Transforms/SimpleLoopUnswitch/guards.ll
    llvm/test/Transforms/SimpleLoopUnswitch/nontrivial-unswitch-cost.ll
    llvm/test/Transforms/SimpleLoopUnswitch/nontrivial-unswitch.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp b/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
index 8f9db3db26c4..4a82fd939dae 100644
--- a/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
+++ b/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
@@ -26,7 +26,9 @@
 #include "llvm/Analysis/LoopPass.h"
 #include "llvm/Analysis/MemorySSA.h"
 #include "llvm/Analysis/MemorySSAUpdater.h"
+#include "llvm/Analysis/MustExecute.h"
 #include "llvm/Analysis/Utils/Local.h"
+#include "llvm/Analysis/ValueTracking.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/Constant.h"
 #include "llvm/IR/Constants.h"
@@ -180,11 +182,14 @@ static void buildPartialUnswitchConditionalBranch(BasicBlock &BB,
                                                   ArrayRef<Value *> Invariants,
                                                   bool Direction,
                                                   BasicBlock &UnswitchedSucc,
-                                                  BasicBlock &NormalSucc) {
+                                                  BasicBlock &NormalSucc,
+                                                  bool insertFreeze) {
   IRBuilder<> IRB(&BB);
-  
+
   Value *Cond = Direction ? IRB.CreateOr(Invariants) :
     IRB.CreateAnd(Invariants);
+  if (insertFreeze)
+    Cond = IRB.CreateFreeze(Cond, Cond->getName() + ".fr");
   IRB.CreateCondBr(Cond, Direction ? &UnswitchedSucc : &NormalSucc,
                    Direction ? &NormalSucc : &UnswitchedSucc);
 }
@@ -498,7 +503,7 @@ static bool unswitchTrivialBranch(Loop &L, BranchInst &BI, DominatorTree &DT,
                  Instruction::And &&
              "Must have an `and` of `i1`s for the condition!");
     buildPartialUnswitchConditionalBranch(*OldPH, Invariants, ExitDirection,
-                                          *UnswitchedBB, *NewPH);
+                                          *UnswitchedBB, *NewPH, false);
   }
 
   // Update the dominator tree with the added edge.
@@ -2009,6 +2014,10 @@ static void unswitchNontrivialInvariants(
       SE->forgetTopmostLoop(&L);
   }
 
+  ICFLoopSafetyInfo SafetyInfo(&DT);
+  SafetyInfo.computeLoopSafetyInfo(&L);
+  bool insertFreeze = !SafetyInfo.isGuaranteedToExecute(TI, &DT, &L);
+
   // If the edge from this terminator to a successor dominates that successor,
   // store a map from each block in its dominator subtree to it. This lets us
   // tell when cloning for a particular successor if a block is dominated by
@@ -2066,6 +2075,12 @@ static void unswitchNontrivialInvariants(
       BasicBlock *ClonedPH = ClonedPHs.begin()->second;
       BI->setSuccessor(ClonedSucc, ClonedPH);
       BI->setSuccessor(1 - ClonedSucc, LoopPH);
+      if (insertFreeze) {
+        auto Cond = BI->getCondition();
+        if (!isGuaranteedNotToBeUndefOrPoison(Cond))
+          BI->setCondition(new FreezeInst(Cond, Cond->getName() + ".fr", BI));
+      }
+
       DTUpdates.push_back({DominatorTree::Insert, SplitBB, ClonedPH});
     } else {
       assert(SI && "Must either be a branch or switch!");
@@ -2080,6 +2095,12 @@ static void unswitchNontrivialInvariants(
         else
           Case.setSuccessor(ClonedPHs.find(Case.getCaseSuccessor())->second);
 
+      if (insertFreeze) {
+        auto Cond = SI->getCondition();
+        if (!isGuaranteedNotToBeUndefOrPoison(Cond))
+          SI->setCondition(new FreezeInst(Cond, Cond->getName() + ".fr", SI));
+      }
+
       // We need to use the set to populate domtree updates as even when there
       // are multiple cases pointing at the same successor we only want to
       // remove and insert one edge in the domtree.
@@ -2156,7 +2177,7 @@ static void unswitchNontrivialInvariants(
     // When doing a partial unswitch, we have to do a bit more work to build up
     // the branch in the split block.
     buildPartialUnswitchConditionalBranch(*SplitBB, Invariants, Direction,
-                                          *ClonedPH, *LoopPH);
+                                          *ClonedPH, *LoopPH, insertFreeze);
     DTUpdates.push_back({DominatorTree::Insert, SplitBB, ClonedPH});
 
     if (MSSAU) {

diff  --git a/llvm/test/Transforms/SimpleLoopUnswitch/exponential-nontrivial-unswitch-nested.ll b/llvm/test/Transforms/SimpleLoopUnswitch/exponential-nontrivial-unswitch-nested.ll
index d2ca06357cfe..04d027cd502c 100644
--- a/llvm/test/Transforms/SimpleLoopUnswitch/exponential-nontrivial-unswitch-nested.ll
+++ b/llvm/test/Transforms/SimpleLoopUnswitch/exponential-nontrivial-unswitch-nested.ll
@@ -85,8 +85,14 @@
 
 declare void @bar()
 
-define void @loop_nested3_conds5(i32* %addr, i1 %c1, i1 %c2, i1 %c3, i1 %c4, i1 %c5) {
+define void @loop_nested3_conds5(i32* %addr, i1 %c1i, i1 %c2i, i1 %c3i, i1 %c4i, i1 %c5i) {
 entry:
+  ; c1 ~ c5 are guaranteed to be never undef or poison.
+  %c1 = freeze i1 %c1i
+  %c2 = freeze i1 %c2i
+  %c3 = freeze i1 %c3i
+  %c4 = freeze i1 %c4i
+  %c5 = freeze i1 %c5i
   %addr1 = getelementptr i32, i32* %addr, i64 0
   %addr2 = getelementptr i32, i32* %addr, i64 1
   %addr3 = getelementptr i32, i32* %addr, i64 2

diff  --git a/llvm/test/Transforms/SimpleLoopUnswitch/exponential-nontrivial-unswitch-nested2.ll b/llvm/test/Transforms/SimpleLoopUnswitch/exponential-nontrivial-unswitch-nested2.ll
index e8879e79c53f..26179ad9068e 100644
--- a/llvm/test/Transforms/SimpleLoopUnswitch/exponential-nontrivial-unswitch-nested2.ll
+++ b/llvm/test/Transforms/SimpleLoopUnswitch/exponential-nontrivial-unswitch-nested2.ll
@@ -97,8 +97,14 @@
 
 declare void @bar()
 
-define void @loop_nested3_conds5(i32* %addr, i1 %c1, i1 %c2, i1 %c3, i1 %c4, i1 %c5) {
+define void @loop_nested3_conds5(i32* %addr, i1 %c1i, i1 %c2i, i1 %c3i, i1 %c4i, i1 %c5i) {
 entry:
+  ; c1 ~ c5 are guaranteed to be never undef or poison.
+  %c1 = freeze i1 %c1i
+  %c2 = freeze i1 %c2i
+  %c3 = freeze i1 %c3i
+  %c4 = freeze i1 %c4i
+  %c5 = freeze i1 %c5i
   %addr1 = getelementptr i32, i32* %addr, i64 0
   %addr2 = getelementptr i32, i32* %addr, i64 1
   %addr3 = getelementptr i32, i32* %addr, i64 2

diff  --git a/llvm/test/Transforms/SimpleLoopUnswitch/exponential-switch-unswitch.ll b/llvm/test/Transforms/SimpleLoopUnswitch/exponential-switch-unswitch.ll
index 35d431e5ee26..6606a1931d4d 100644
--- a/llvm/test/Transforms/SimpleLoopUnswitch/exponential-switch-unswitch.ll
+++ b/llvm/test/Transforms/SimpleLoopUnswitch/exponential-switch-unswitch.ll
@@ -86,8 +86,11 @@
 ; LOOP-MAX-COUNT-111:     Loop at depth 2 containing:
 ; LOOP-MAX-NOT: Loop at depth 2 containing:
 
-define i32 @loop_switch(i32* %addr, i32 %c1, i32 %c2) {
+define i32 @loop_switch(i32* %addr, i32 %c1i, i32 %c2i) {
 entry:
+  ; c1, c2 are guaranteed to be never undef or poison.
+  %c1 = freeze i32 %c1i
+  %c2 = freeze i32 %c2i
   %addr1 = getelementptr i32, i32* %addr, i64 0
   %addr2 = getelementptr i32, i32* %addr, i64 1
   %check0 = icmp eq i32 %c2, 0

diff  --git a/llvm/test/Transforms/SimpleLoopUnswitch/guards.ll b/llvm/test/Transforms/SimpleLoopUnswitch/guards.ll
index de57075b6222..9365829f976a 100644
--- a/llvm/test/Transforms/SimpleLoopUnswitch/guards.ll
+++ b/llvm/test/Transforms/SimpleLoopUnswitch/guards.ll
@@ -81,7 +81,8 @@ exit:
 define void @test_conditional_guards(i1 %cond, i32 %N) {
 ; CHECK-LABEL: @test_conditional_guards(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    br i1 [[COND:%.*]], label [[ENTRY_SPLIT_US:%.*]], label [[ENTRY_SPLIT:%.*]]
+; CHECK-NEXT:    [[COND_FR:%.*]] = freeze i1 [[COND:%.*]]
+; CHECK-NEXT:    br i1 [[COND_FR]], label [[ENTRY_SPLIT_US:%.*]], label [[ENTRY_SPLIT:%.*]]
 ; CHECK:       entry.split.us:
 ; CHECK-NEXT:    br label [[LOOP_US:%.*]]
 ; CHECK:       loop.us:

diff  --git a/llvm/test/Transforms/SimpleLoopUnswitch/nontrivial-unswitch-cost.ll b/llvm/test/Transforms/SimpleLoopUnswitch/nontrivial-unswitch-cost.ll
index 692799db1c60..7b2c8280e7a3 100644
--- a/llvm/test/Transforms/SimpleLoopUnswitch/nontrivial-unswitch-cost.ll
+++ b/llvm/test/Transforms/SimpleLoopUnswitch/nontrivial-unswitch-cost.ll
@@ -57,7 +57,8 @@ define void @test_unswitch(i1* %ptr, i1 %cond) {
 entry:
   br label %loop_begin
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    br i1 %cond, label %entry.split.us, label %entry.split
+; CHECK-NEXT:    %[[COND_FR:.*]] = freeze i1 %cond
+; CHECK-NEXT:    br i1 %[[COND_FR]], label %entry.split.us, label %entry.split
 
 loop_begin:
   call void @x()
@@ -127,7 +128,8 @@ define void @test_unswitch_non_dup_code(i1* %ptr, i1 %cond) {
 entry:
   br label %loop_begin
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    br i1 %cond, label %entry.split.us, label %entry.split
+; CHECK-NEXT:    %[[COND_FR:.*]] = freeze i1 %cond
+; CHECK-NEXT:    br i1 %[[COND_FR]], label %entry.split.us, label %entry.split
 
 loop_begin:
   call void @x()
@@ -208,7 +210,8 @@ define void @test_unswitch_non_dup_code_in_cfg(i1* %ptr, i1 %cond) {
 entry:
   br label %loop_begin
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    br i1 %cond, label %entry.split.us, label %entry.split
+; CHECK-NEXT:    %[[COND_FR:.*]] = freeze i1 %cond
+; CHECK-NEXT:    br i1 %[[COND_FR]], label %entry.split.us, label %entry.split
 
 loop_begin:
   call void @x()
@@ -364,7 +367,8 @@ define void @test_unswitch_large_exit(i1* %ptr, i1 %cond) {
 entry:
   br label %loop_begin
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    br i1 %cond, label %entry.split.us, label %entry.split
+; CHECK-NEXT:    %[[COND_FR:.*]] = freeze i1 %cond
+; CHECK-NEXT:    br i1 %[[COND_FR]], label %entry.split.us, label %entry.split
 
 loop_begin:
   call void @x()
@@ -441,7 +445,8 @@ define void @test_unswitch_dedicated_exiting(i1* %ptr, i1 %cond) {
 entry:
   br label %loop_begin
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    br i1 %cond, label %entry.split.us, label %entry.split
+; CHECK-NEXT:    %[[COND_FR:.*]] = freeze i1 %cond
+; CHECK-NEXT:    br i1 %[[COND_FR]], label %entry.split.us, label %entry.split
 
 loop_begin:
   call void @x()

diff  --git a/llvm/test/Transforms/SimpleLoopUnswitch/nontrivial-unswitch.ll b/llvm/test/Transforms/SimpleLoopUnswitch/nontrivial-unswitch.ll
index 0aec52d447d5..02b3bd5b4c3d 100644
--- a/llvm/test/Transforms/SimpleLoopUnswitch/nontrivial-unswitch.ll
+++ b/llvm/test/Transforms/SimpleLoopUnswitch/nontrivial-unswitch.ll
@@ -814,7 +814,8 @@ inner_loop_begin:
 ; CHECK-NEXT:    %[[A_INNER_PHI:.*]] = phi i32 [ %[[A]], %loop_begin ], [ %[[A2:.*]], %inner_inner_loop_exit ]
 ; CHECK-NEXT:    %[[COND:.*]] = load i1, i1* %cond.ptr
 ; CHECK-NEXT:    %[[B:.*]] = load i32, i32* %b.ptr
-; CHECK-NEXT:    br i1 %[[COND]], label %inner_loop_begin.split.us, label %inner_loop_begin.split
+; CHECK-NEXT:    %[[COND_FR:.*]] = freeze i1 %[[COND]]
+; CHECK-NEXT:    br i1 %[[COND_FR]], label %inner_loop_begin.split.us, label %inner_loop_begin.split
 
 inner_inner_loop_begin:
   %v1 = load i1, i1* %ptr
@@ -967,7 +968,8 @@ inner_loop_begin:
 ; CHECK-NEXT:    %[[A_INNER_PHI:.*]] = phi i32 [ %[[A]], %loop_begin ], [ %[[A2:.*]], %inner_inner_loop_exit ]
 ; CHECK-NEXT:    %[[COND:.*]] = load i1, i1* %cond.ptr
 ; CHECK-NEXT:    %[[B:.*]] = load i32, i32* %b.ptr
-; CHECK-NEXT:    br i1 %[[COND]], label %inner_loop_begin.split.us, label %inner_loop_begin.split
+; CHECK-NEXT:    %[[COND_FR:.*]] = freeze i1 %[[COND]]
+; CHECK-NEXT:    br i1 %[[COND_FR]], label %inner_loop_begin.split.us, label %inner_loop_begin.split
 
 inner_inner_loop_begin:
   %v1 = load i1, i1* %ptr
@@ -1120,7 +1122,8 @@ inner_loop_begin:
 ; CHECK-NEXT:    %[[A_INNER_PHI:.*]] = phi i32 [ %[[A]], %loop_begin ], [ %[[A2:.*]], %inner_inner_loop_exit ]
 ; CHECK-NEXT:    %[[COND:.*]] = load i1, i1* %cond.ptr
 ; CHECK-NEXT:    %[[B:.*]] = load i32, i32* %b.ptr
-; CHECK-NEXT:    br i1 %[[COND]], label %inner_loop_begin.split.us, label %inner_loop_begin.split
+; CHECK-NEXT:    %[[COND_FR:.*]] = freeze i1 %[[COND]]
+; CHECK-NEXT:    br i1 %[[COND_FR]], label %inner_loop_begin.split.us, label %inner_loop_begin.split
 
 inner_inner_loop_begin:
   %v1 = load i1, i1* %ptr
@@ -1240,7 +1243,8 @@ inner_loop_begin:
 ; CHECK-NEXT:    %[[A_INNER_PHI:.*]] = phi i32 [ %[[A]], %loop_begin ], [ %[[A2:.*]], %inner_inner_loop_exit ]
 ; CHECK-NEXT:    %[[COND:.*]] = load i1, i1* %cond.ptr
 ; CHECK-NEXT:    %[[B:.*]] = load i32, i32* %b.ptr
-; CHECK-NEXT:    br i1 %[[COND]], label %inner_loop_begin.split.us, label %inner_loop_begin.split
+; CHECK-NEXT:    %[[COND_FR:.*]] = freeze i1 %[[COND]]
+; CHECK-NEXT:    br i1 %[[COND_FR]], label %inner_loop_begin.split.us, label %inner_loop_begin.split
 
 inner_inner_loop_begin:
   %v1 = load i1, i1* %ptr
@@ -1482,7 +1486,8 @@ define i32 @test10a(i1* %ptr, i1 %cond, i32* %a.ptr) {
 entry:
   br label %loop_begin
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    br i1 %cond, label %entry.split.us, label %entry.split
+; CHECK-NEXT:    %[[COND_FR:.*]] = freeze i1 %cond
+; CHECK-NEXT:    br i1 %[[COND_FR]], label %entry.split.us, label %entry.split
 
 loop_begin:
   %a = load i32, i32* %a.ptr
@@ -1562,7 +1567,8 @@ define i32 @test10b(i1* %ptr, i1 %cond, i32* %a.ptr) {
 entry:
   br label %loop_begin
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    br i1 %cond, label %entry.split.us, label %entry.split
+; CHECK-NEXT:    %[[COND_FR:.*]] = freeze i1 %cond
+; CHECK-NEXT:    br i1 %[[COND_FR]], label %entry.split.us, label %entry.split
 
 loop_begin:
   %a = load i32, i32* %a.ptr
@@ -1661,7 +1667,8 @@ inner_loop_ph:
   br label %inner_loop_begin
 ; CHECK:       inner_loop_ph:
 ; CHECK-NEXT:    %[[COND:.*]] = load i1, i1* %cond.ptr
-; CHECK-NEXT:    br i1 %[[COND]], label %inner_loop_ph.split.us, label %inner_loop_ph.split
+; CHECK-NEXT:    %[[COND_FR:.*]] = freeze i1 %[[COND]]
+; CHECK-NEXT:    br i1 %[[COND_FR]], label %inner_loop_ph.split.us, label %inner_loop_ph.split
 
 inner_loop_begin:
   call void @sink1(i32 %b)
@@ -1755,7 +1762,8 @@ inner_loop_ph:
   br label %inner_loop_begin
 ; CHECK:       inner_loop_ph:
 ; CHECK-NEXT:    %[[COND:.*]] = load i1, i1* %cond.ptr
-; CHECK-NEXT:    br i1 %[[COND]], label %inner_loop_ph.split.us, label %inner_loop_ph.split
+; CHECK-NEXT:    %[[COND_FR:.*]] = freeze i1 %[[COND]]
+; CHECK-NEXT:    br i1 %[[COND_FR]], label %inner_loop_ph.split.us, label %inner_loop_ph.split
 
 inner_loop_begin:
   call void @sink1(i32 %b)
@@ -1853,7 +1861,8 @@ inner_inner_loop_ph:
   br label %inner_inner_loop_begin
 ; CHECK:       inner_inner_loop_ph:
 ; CHECK-NEXT:    %[[COND:.*]] = load i1, i1* %cond.ptr
-; CHECK-NEXT:    br i1 %[[COND]], label %inner_inner_loop_ph.split.us, label %inner_inner_loop_ph.split
+; CHECK-NEXT:    %[[COND_FR:.*]] = freeze i1 %[[COND]]
+; CHECK-NEXT:    br i1 %[[COND_FR]], label %inner_inner_loop_ph.split.us, label %inner_inner_loop_ph.split
 
 inner_inner_loop_begin:
   call void @sink1(i32 %b)
@@ -1961,7 +1970,8 @@ inner_inner_loop_ph:
   br label %inner_inner_loop_begin
 ; CHECK:       inner_inner_loop_ph:
 ; CHECK-NEXT:    %[[COND:.*]] = load i1, i1* %cond.ptr
-; CHECK-NEXT:    br i1 %[[COND]], label %inner_inner_loop_ph.split.us, label %inner_inner_loop_ph.split
+; CHECK-NEXT:    %[[COND_FR:.*]] = freeze i1 %[[COND]]
+; CHECK-NEXT:    br i1 %[[COND_FR]], label %inner_inner_loop_ph.split.us, label %inner_inner_loop_ph.split
 
 inner_inner_loop_begin:
   call void @sink1(i32 %b)
@@ -2048,7 +2058,8 @@ define i32 @test13a(i1* %ptr, i1 %cond, i32* %a.ptr, i32* %b.ptr) {
 entry:
   br label %loop_begin
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    br i1 %cond, label %entry.split.us, label %entry.split
+; CHECK-NEXT:    %[[COND_FR:.*]] = freeze i1 %cond
+; CHECK-NEXT:    br i1 %[[COND_FR]], label %entry.split.us, label %entry.split
 
 loop_begin:
   %a = load i32, i32* %a.ptr
@@ -2172,7 +2183,8 @@ define i32 @test13b(i1* %ptr, i1 %cond, i32* %a.ptr, i32* %b.ptr) {
 entry:
   br label %loop_begin
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    br i1 %cond, label %entry.split.us, label %entry.split
+; CHECK-NEXT:    %[[COND_FR:.*]] = freeze i1 %cond
+; CHECK-NEXT:    br i1 %[[COND_FR]], label %entry.split.us, label %entry.split
 
 loop_begin:
   %a = load i32, i32* %a.ptr
@@ -2420,9 +2432,10 @@ loop_exit:
 ; paths to reach an inner loop after unswitching, and one of them is via the
 ; predecessors of the unswitched loop header. That can allow us to find the loop
 ; through multiple 
diff erent paths.
-define void @test21(i1 %a, i1 %b) {
+define void @test21(i1 %a0, i1 %b) {
 ; CHECK-LABEL: @test21(
 bb:
+  %a = freeze i1 %a0
   br label %bb3
 ; CHECK-NOT:     br i1 %a
 ;
@@ -2553,7 +2566,8 @@ define void @test23(i1 %arg, i1* %ptr) {
 entry:
   br label %outer.header
 ; CHECK:       entry:
-; CHECK-NEXT:    br i1 %arg,
+; CHECK-NEXT:    %[[ARG_FR:.*]] = freeze i1 %arg
+; CHECK-NEXT:    br i1 %[[ARG_FR]],
 ;
 ; Just verify that we unswitched the correct bits. We should call `@f` twice in
 ; one unswitch and `@f` and then `@g` in the other.
@@ -3064,7 +3078,8 @@ define i32 @test29(i32 %arg) {
 entry:
   br label %header
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    switch i32 %arg, label %[[ENTRY_SPLIT_C:.*]] [
+; CHECK-NEXT:    %arg.fr = freeze i32 %arg
+; CHECK-NEXT:    switch i32 %arg.fr, label %[[ENTRY_SPLIT_C:.*]] [
 ; CHECK-NEXT:      i32 0, label %[[ENTRY_SPLIT_A:.*]]
 ; CHECK-NEXT:      i32 1, label %[[ENTRY_SPLIT_A]]
 ; CHECK-NEXT:      i32 2, label %[[ENTRY_SPLIT_B:.*]]
@@ -3242,11 +3257,13 @@ exit:
 ; 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 @test30(i32 %arg) {
+define i32 @test30(i32 %arg0) {
 ; CHECK-LABEL: define i32 @test30(
 entry:
+  %arg = freeze i32 %arg0
   br label %header
 ; CHECK-NEXT:  entry:
+; CHECK-NEXT:    %arg = freeze i32 %arg0
 ; CHECK-NEXT:    switch i32 %arg, label %[[ENTRY_SPLIT_EXIT:.*]] [
 ; CHECK-NEXT:      i32 -1, label %[[ENTRY_SPLIT_EXIT]]
 ; CHECK-NEXT:      i32 0, label %[[ENTRY_SPLIT_A:.*]]
@@ -3426,7 +3443,8 @@ b.header:
   br label %c.header
 ; CHECK:       b.header:
 ; CHECK-NEXT:    %v1 = call i1 @cond()
-; CHECK-NEXT:    br i1 %v1, label %[[B_HEADER_SPLIT_US:.*]], label %[[B_HEADER_SPLIT:.*]]
+; CHECK-NEXT:    %[[V1_FR:.*]] = freeze i1 %v1
+; CHECK-NEXT:    br i1 %[[V1_FR]], label %[[B_HEADER_SPLIT_US:.*]], label %[[B_HEADER_SPLIT:.*]]
 ;
 ; CHECK:       [[B_HEADER_SPLIT_US]]:
 ; CHECK-NEXT:    br label %[[C_HEADER_US:.*]]
@@ -3501,7 +3519,8 @@ b.header:
 ; CHECK:       b.header:
 ; CHECK-NEXT:    %x.b = load i32, i32* %ptr
 ; CHECK-NEXT:    %v1 = call i1 @cond()
-; CHECK-NEXT:    br i1 %v1, label %[[B_HEADER_SPLIT_US:.*]], label %[[B_HEADER_SPLIT:.*]]
+; CHECK-NEXT:    %[[V1_FR:.*]] = freeze i1 %v1
+; CHECK-NEXT:    br i1 %[[V1_FR]], label %[[B_HEADER_SPLIT_US:.*]], label %[[B_HEADER_SPLIT:.*]]
 ;
 ; CHECK:       [[B_HEADER_SPLIT_US]]:
 ; CHECK-NEXT:    br label %[[C_HEADER_US:.*]]
@@ -3589,7 +3608,8 @@ b.header:
 ; CHECK:       b.header:
 ; CHECK-NEXT:    %x.b = load i32, i32* %ptr
 ; CHECK-NEXT:    %v1 = call i1 @cond()
-; CHECK-NEXT:    br i1 %v1, label %[[B_HEADER_SPLIT_US:.*]], label %[[B_HEADER_SPLIT:.*]]
+; CHECK-NEXT:    %[[V1_FR:.*]] = freeze i1 %v1
+; CHECK-NEXT:    br i1 %[[V1_FR]], label %[[B_HEADER_SPLIT_US:.*]], label %[[B_HEADER_SPLIT:.*]]
 ;
 ; CHECK:       [[B_HEADER_SPLIT_US]]:
 ; CHECK-NEXT:    br label %[[C_HEADER_US:.*]]
@@ -3669,7 +3689,8 @@ b.header:
 ; CHECK:       b.header:
 ; CHECK-NEXT:    %x.b = load i32, i32* %ptr
 ; CHECK-NEXT:    %v1 = call i1 @cond()
-; CHECK-NEXT:    br i1 %v1, label %[[B_HEADER_SPLIT_US:.*]], label %[[B_HEADER_SPLIT:.*]]
+; CHECK-NEXT:    %[[V1_FR:.*]] = freeze i1 %v1
+; CHECK-NEXT:    br i1 %[[V1_FR]], label %[[B_HEADER_SPLIT_US:.*]], label %[[B_HEADER_SPLIT:.*]]
 ;
 ; CHECK:       [[B_HEADER_SPLIT_US]]:
 ; CHECK-NEXT:    br label %[[C_HEADER_US:.*]]
@@ -3767,7 +3788,8 @@ c.header:
   br label %d.header
 ; CHECK:       c.header:
 ; CHECK-NEXT:    %v1 = call i1 @cond()
-; CHECK-NEXT:    br i1 %v1, label %[[C_HEADER_SPLIT_US:.*]], label %[[C_HEADER_SPLIT:.*]]
+; CHECK-NEXT:    %[[V1_FR:.*]] = freeze i1 %v1
+; CHECK-NEXT:    br i1 %[[V1_FR]], label %[[C_HEADER_SPLIT_US:.*]], label %[[C_HEADER_SPLIT:.*]]
 ;
 ; CHECK:       [[C_HEADER_SPLIT_US]]:
 ; CHECK-NEXT:    br label %[[D_HEADER_US:.*]]
@@ -3880,7 +3902,8 @@ c.header:
 ; CHECK:       c.header:
 ; CHECK-NEXT:    %x.c = load i32, i32* %ptr
 ; CHECK-NEXT:    %v1 = call i1 @cond()
-; CHECK-NEXT:    br i1 %v1, label %[[C_HEADER_SPLIT_US:.*]], label %[[C_HEADER_SPLIT:.*]]
+; CHECK-NEXT:    %[[V1_FR:.*]] = freeze i1 %v1
+; CHECK-NEXT:    br i1 %[[V1_FR]], label %[[C_HEADER_SPLIT_US:.*]], label %[[C_HEADER_SPLIT:.*]]
 ;
 ; CHECK:       [[C_HEADER_SPLIT_US]]:
 ; CHECK-NEXT:    br label %[[D_HEADER_US:.*]]
@@ -3962,7 +3985,8 @@ b.header:
 ; CHECK:       b.header:
 ; CHECK-NEXT:    %x.b = load i32, i32* %ptr
 ; CHECK-NEXT:    %v1 = call i32 @cond.i32()
-; CHECK-NEXT:    switch i32 %v1, label %[[B_HEADER_SPLIT:.*]] [
+; CHECK-NEXT:    %[[V1_FR]] = freeze i32 %v1
+; CHECK-NEXT:    switch i32 %[[V1_FR]], label %[[B_HEADER_SPLIT:.*]] [
 ; CHECK-NEXT:      i32 1, label %[[B_HEADER_SPLIT_US:.*]]
 ; CHECK-NEXT:      i32 2, label %[[B_HEADER_SPLIT_US]]
 ; CHECK-NEXT:      i32 3, label %[[B_HEADER_SPLIT_US]]


        


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