[LICM] Hoisting of widenable conditions out of loops

The change itself is straight forward and obvious, but ... there's an existing test checking for exactly the opposite. Both I and Artur think this is simply conservatism in the initial implementation.  If anyone bisects a problem to this, a counter example will be very interesting.

Differential Revision: https://reviews.llvm.org/D69907

Author: preames

llvm/include/llvm/IR/Intrinsics.td

@@ -1070,7 +1070,7 @@ def int_experimental_guard : Intrinsic<[], [llvm_i1_ty, llvm_vararg_ty],
 
 // Supports widenable conditions for guards represented as explicit branches.
 def int_experimental_widenable_condition : Intrinsic<[llvm_i1_ty], [],
-                                           [IntrInaccessibleMemOnly, IntrWillReturn]>;
+        [IntrInaccessibleMemOnly, IntrWillReturn, IntrSpeculatable]>;
 
 // NOP: calls/invokes to this intrinsic are removed by codegen
 def int_donothing : Intrinsic<[], [], [IntrNoMem, IntrWillReturn]>;

llvm/lib/Transforms/Scalar/LICM.cpp

@@ -1144,6 +1144,10 @@ bool llvm::canSinkOrHoistInst(Instruction &I, AAResults *AA, DominatorTree *DT,
       // Assumes don't actually alias anything or throw
       return true;
 
+    if (match(CI, m_Intrinsic<Intrinsic::experimental_widenable_condition>()))
+      // Widenable conditions don't actually alias anything or throw
+      return true;
+
     // Handle simple cases by querying alias analysis.
     FunctionModRefBehavior Behavior = AA->getModRefBehavior(CI);
     if (Behavior == FMRB_DoesNotAccessMemory)

llvm/test/Transforms/LICM/explicit_guards.ll

@@ -2,21 +2,54 @@
 ; RUN: opt -S -make-guards-explicit -basicaa -licm < %s        | FileCheck %s
 ; RUN: opt -S -aa-pipeline=basic-aa -passes='require<opt-remark-emit>,make-guards-explicit,loop(licm)' < %s | FileCheck %s
 
-; Test interaction between explicit guards and LICM: make sure that we do not
-; hoist explicit conditions while we can hoist invariant loads in presence of
-; explicit guards.
-
 declare void @llvm.experimental.guard(i1,...)
+declare void @maythrow()
 
 ; Make sure that we do not hoist widenable_cond out of loop.
-define void @do_not_hoist_widenable_cond(i1 %cond, i32 %N, i32 %M) {
-; CHECK-LABEL: @do_not_hoist_widenable_cond(
+define void @hoist_widenable_cond(i1 %cond, i32 %N, i32 %M) {
+; CHECK-LABEL: @hoist_widenable_cond(
 ; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[WIDENABLE_COND:%.*]] = call i1 @llvm.experimental.widenable.condition()
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
 ; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[GUARDED:%.*]] ]
 ; CHECK-NEXT:    [[GUARD_COND:%.*]] = icmp slt i32 [[IV]], [[N:%.*]]
+; CHECK-NEXT:    [[EXIPLICIT_GUARD_COND:%.*]] = and i1 [[GUARD_COND]], [[WIDENABLE_COND]]
+; CHECK-NEXT:    br i1 [[EXIPLICIT_GUARD_COND]], label [[GUARDED]], label [[DEOPT:%.*]], !prof !0
+; CHECK:       deopt:
+; CHECK-NEXT:    call void (...) @llvm.experimental.deoptimize.isVoid() [ "deopt"() ]
+; CHECK-NEXT:    ret void
+; CHECK:       guarded:
+; CHECK-NEXT:    [[LOOP_COND:%.*]] = icmp slt i32 [[IV]], [[M:%.*]]
+; CHECK-NEXT:    [[IV_NEXT]] = add i32 [[IV]], 1
+; CHECK-NEXT:    br i1 [[LOOP_COND]], label [[LOOP]], label [[EXIT:%.*]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %loop
+
+loop:
+  %iv = phi i32 [ 0, %entry ], [ %iv.next, %loop ]
+  %guard_cond = icmp slt i32 %iv, %N
+  call void(i1, ...) @llvm.experimental.guard(i1 %guard_cond) [ "deopt"() ]
+  %loop_cond = icmp slt i32 %iv, %M
+  %iv.next = add i32 %iv, 1
+  br i1 %loop_cond, label %loop, label %exit
+
+exit:
+  ret void
+}
+
+define void @hoist_widenable_cond_speculate(i1 %cond, i32 %N, i32 %M) {
+; CHECK-LABEL: @hoist_widenable_cond_speculate(
+; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[WIDENABLE_COND:%.*]] = call i1 @llvm.experimental.widenable.condition()
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[GUARDED:%.*]] ]
+; CHECK-NEXT:    [[GUARD_COND:%.*]] = icmp slt i32 [[IV]], [[N:%.*]]
+; CHECK-NEXT:    call void @maythrow()
 ; CHECK-NEXT:    [[EXIPLICIT_GUARD_COND:%.*]] = and i1 [[GUARD_COND]], [[WIDENABLE_COND]]
 ; CHECK-NEXT:    br i1 [[EXIPLICIT_GUARD_COND]], label [[GUARDED]], label [[DEOPT:%.*]], !prof !0
 ; CHECK:       deopt:
@@ -35,6 +68,7 @@ entry:
 loop:
   %iv = phi i32 [ 0, %entry ], [ %iv.next, %loop ]
   %guard_cond = icmp slt i32 %iv, %N
+  call void @maythrow()
   call void(i1, ...) @llvm.experimental.guard(i1 %guard_cond) [ "deopt"() ]
   %loop_cond = icmp slt i32 %iv, %M
   %iv.next = add i32 %iv, 1
@@ -44,15 +78,16 @@ exit:
   ret void
 }
 
+
 define void @hoist_invariant_load(i1 %cond, i32* %np, i32 %M) {
 ; CHECK-LABEL: @hoist_invariant_load(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[N:%.*]] = load i32, i32* [[NP:%.*]]
+; CHECK-NEXT:    [[WIDENABLE_COND:%.*]] = call i1 @llvm.experimental.widenable.condition()
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
 ; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[GUARDED:%.*]] ]
 ; CHECK-NEXT:    [[GUARD_COND:%.*]] = icmp slt i32 [[IV]], [[N]]
-; CHECK-NEXT:    [[WIDENABLE_COND:%.*]] = call i1 @llvm.experimental.widenable.condition()
 ; CHECK-NEXT:    [[EXIPLICIT_GUARD_COND:%.*]] = and i1 [[GUARD_COND]], [[WIDENABLE_COND]]
 ; CHECK-NEXT:    br i1 [[EXIPLICIT_GUARD_COND]], label [[GUARDED]], label [[DEOPT:%.*]], !prof !0
 ; CHECK:       deopt: