[JumpThreading] Safely replace uses of condition
This patch builds over https://reviews.llvm.org/rL303349 and replaces
the use of the condition only if it is safe to do so.
We should not blindly RAUW the condition if experimental.guard or assume
is a use of that
condition. This is because LVI may have used the guard/assume to
identify the
value of the condition, and RUAWing will fold the guard/assume and uses
before the guards/assumes.
Reviewers: sanjoy, reames, trentxintong, mkazantsev
Reviewed by: sanjoy, reames
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D33257
llvm-svn: 303633
diff --git a/llvm/test/Transforms/JumpThreading/guards.ll b/llvm/test/Transforms/JumpThreading/guards.ll
index c5f72b1..53175a7 100644
--- a/llvm/test/Transforms/JumpThreading/guards.ll
+++ b/llvm/test/Transforms/JumpThreading/guards.ll
@@ -182,86 +182,89 @@
ret void
}
-declare void @never_called()
+declare void @never_called(i1)
-; Assume the guard is always taken and we deoptimize, so we never reach the
-; branch below that guard. We should *never* change the behaviour of a guard from
-; `must deoptimize` to `may deoptimize`, since this affects the program
-; semantics.
+; LVI uses guard to identify value of %c2 in branch as true, we cannot replace that
+; guard with guard(true & c1).
define void @dont_fold_guard(i8* %addr, i32 %i, i32 %length) {
; CHECK-LABEL: dont_fold_guard
-; CHECK: experimental.guard(i1 %wide.chk)
-
-entry:
- br label %BBPred
-
-BBPred:
- %cond = icmp eq i8* %addr, null
- br i1 %cond, label %zero, label %not_zero
-
-zero:
- unreachable
-
-not_zero:
+; CHECK: %wide.chk = and i1 %c1, %c2
+; CHECK-NEXT: experimental.guard(i1 %wide.chk)
+; CHECK-NEXT: call void @never_called(i1 true)
+; CHECK-NEXT: ret void
%c1 = icmp ult i32 %i, %length
%c2 = icmp eq i32 %i, 0
%wide.chk = and i1 %c1, %c2
call void(i1, ...) @llvm.experimental.guard(i1 %wide.chk) [ "deopt"() ]
- br i1 %c2, label %unreachedBB2, label %unreachedBB1
+ br i1 %c2, label %BB1, label %BB2
-unreachedBB2:
- call void @never_called()
+BB1:
+ call void @never_called(i1 %c2)
ret void
-unreachedBB1:
+BB2:
ret void
}
+declare void @dummy(i1) nounwind argmemonly
+; same as dont_fold_guard1 but there's a use immediately after guard and before
+; branch. We can fold that use.
+define void @dont_fold_guard2(i8* %addr, i32 %i, i32 %length) {
+; CHECK-LABEL: dont_fold_guard2
+; CHECK: %wide.chk = and i1 %c1, %c2
+; CHECK-NEXT: experimental.guard(i1 %wide.chk)
+; CHECK-NEXT: dummy(i1 true)
+; CHECK-NEXT: call void @never_called(i1 true)
+; CHECK-NEXT: ret void
+ %c1 = icmp ult i32 %i, %length
+ %c2 = icmp eq i32 %i, 0
+ %wide.chk = and i1 %c1, %c2
+ call void(i1, ...) @llvm.experimental.guard(i1 %wide.chk) [ "deopt"() ]
+ call void @dummy(i1 %c2)
+ br i1 %c2, label %BB1, label %BB2
+
+BB1:
+ call void @never_called(i1 %c2)
+ ret void
+
+BB2:
+ ret void
+}
; same as dont_fold_guard1 but condition %cmp is not an instruction.
; We cannot fold the guard under any circumstance.
; FIXME: We can merge unreachableBB2 into not_zero.
-define void @dont_fold_guard2(i8* %addr, i1 %cmp, i32 %i, i32 %length) {
-; CHECK-LABEL: dont_fold_guard2
+define void @dont_fold_guard3(i8* %addr, i1 %cmp, i32 %i, i32 %length) {
+; CHECK-LABEL: dont_fold_guard3
; CHECK: guard(i1 %cmp)
-
-entry:
- br label %BBPred
-
-BBPred:
- %cond = icmp eq i8* %addr, null
- br i1 %cond, label %zero, label %not_zero
-
-zero:
- unreachable
-
-not_zero:
call void(i1, ...) @llvm.experimental.guard(i1 %cmp) [ "deopt"() ]
- br i1 %cmp, label %unreachedBB2, label %unreachedBB1
+ br i1 %cmp, label %BB1, label %BB2
-unreachedBB2:
- call void @never_called()
+BB1:
+ call void @never_called(i1 %cmp)
ret void
-unreachedBB1:
+BB2:
ret void
}
+declare void @f(i1)
; Same as dont_fold_guard1 but use switch instead of branch.
; triggers source code `ProcessThreadableEdges`.
-declare void @f(i1)
-define void @dont_fold_guard3(i1 %cmp1, i32 %i) nounwind {
-; CHECK-LABEL: dont_fold_guard3
+define void @dont_fold_guard4(i1 %cmp1, i32 %i) nounwind {
+; CHECK-LABEL: dont_fold_guard4
; CHECK-LABEL: L2:
; CHECK-NEXT: %cmp = icmp eq i32 %i, 0
; CHECK-NEXT: guard(i1 %cmp)
-; CHECK-NEXT: @f(i1 %cmp)
+; CHECK-NEXT: dummy(i1 true)
+; CHECK-NEXT: @f(i1 true)
; CHECK-NEXT: ret void
entry:
br i1 %cmp1, label %L0, label %L3
L0:
%cmp = icmp eq i32 %i, 0
call void(i1, ...) @llvm.experimental.guard(i1 %cmp) [ "deopt"() ]
+ call void @dummy(i1 %cmp)
switch i1 %cmp, label %L3 [
i1 false, label %L1
i1 true, label %L2