[GuardWidening] Make sure widened condition operands are available at insertion point

[dmakogon]

Summary

When inserting a widened condition we handle the following special case:

L >u C0 && L >u C1  ->  L >u max(C0, C1)

Recently insertion point finding algorithm changed.
Previously we would insert the new condition right before the conditional branch where all L operands were available.
Now we may choose the widenable condition intrinsic call as insertion point and it may happen so that the L operands are computed after the call, so we have to make sure that L operands are available where we want to insert it.

[mkazantsev]

I think the naming here is extremely confusing and misleading. Can you pls rename isAvailableAt into something that better corresponds to its true semantics in a follow-up patch?

llvm/lib/Transforms/Scalar/GuardWidening.cpp

555

Why is that guaranteed?

[dmakogon]

llvm/lib/Transforms/Scalar/GuardWidening.cpp

555

The caller must guarantee that Cond0 and Cond1 are available at InsertPt if it's not null.
Generally we can always insert Cond0 && Cond1 there, so availability must be guaranteed.

[dmakogon]

In D144944#4157674, @mkazantsev wrote:

I think the naming here is extremely confusing and misleading. Can you pls rename isAvailableAt into something that better corresponds to its true semantics in a follow-up patch?

Yeah, agree. Will do this as a follow-up.

[dmakogon]

llvm/lib/Transforms/Scalar/GuardWidening.cpp

555

The caller must guarantee that Cond0 and Cond1 are available at InsertPt if it's not null.

... and in this case L is an operand of Cond0 so it must be available too.

[mkazantsev]

Ok, thanks for clarification!

llvm/lib/Transforms/Scalar/GuardWidening.cpp

if (match(Cond0, m_ICmp(Pred0, m_Value(LHS), m_ConstantInt(RHS0))) &&
       if (std::optional<ConstantRange> Intersect =
               CR0.exactIntersectWith(CR1)) {
         APInt NewRHSAP;
         CmpInst::Predicate Pred;
         if (Intersect->getEquivalentICmp(Pred, NewRHSAP)) {
           if (InsertPt) {
             ConstantInt *NewRHS =
                 ConstantInt::get(Cond0->getContext(), NewRHSAP);
+            assert(isAvailableAt(LHS, InsertPt) && "must be");
+            makeAvailableAt(LHS, InsertPt);
             Result = new ICmpInst(InsertPt, Pred, LHS, NewRHS, "wide.chk");
           }
           return true;
         }
       }
     }
   }
 

llvm/test/Transforms/GuardWidening/widen-cond-with-operands.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt -S -passes=guard-widening,verify < %s | FileCheck %s
 target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128-ni:1-p2:32:8:8:32-ni:2"
 target triple = "x86_64-unknown-linux-gnu"
 
-; REQUIRES: asserts
-; XFAIL: *
-
-; GuardWidening moves 'check' instruction before 'wc1' without its operand ('zero').
-; This is incorrect as 'zero' is not available at that point.
+; Make sure GuardWidening moves 'check' instruction before 'wc1' together with its operand - 'zero'.
 define void @foo() {
+; CHECK-LABEL: @foo(
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    [[ZERO:%.*]] = add i32 0, 0
+; CHECK-NEXT:    [[WIDE_CHK:%.*]] = icmp ult i32 [[ZERO]], 0
+; CHECK-NEXT:    [[WC1:%.*]] = call i1 @llvm.experimental.widenable.condition()
+; CHECK-NEXT:    [[WC2:%.*]] = call i1 @llvm.experimental.widenable.condition()
+; CHECK-NEXT:    [[CHECK:%.*]] = icmp ult i32 [[ZERO]], 0
+; CHECK-NEXT:    [[C2:%.*]] = and i1 [[CHECK]], [[WC2]]
+; CHECK-NEXT:    [[C1:%.*]] = and i1 [[WIDE_CHK]], [[WC1]]
+; CHECK-NEXT:    br i1 [[C1]], label [[BB6:%.*]], label [[BB9:%.*]]
+; CHECK:       bb6:
+; CHECK-NEXT:    br i1 true, label [[BB7:%.*]], label [[BB8:%.*]]
+; CHECK:       bb7:
+; CHECK-NEXT:    ret void
+; CHECK:       bb8:
+; CHECK-NEXT:    call void (...) @llvm.experimental.deoptimize.isVoid(i32 0) [ "deopt"() ]
+; CHECK-NEXT:    ret void
+; CHECK:       bb9:
+; CHECK-NEXT:    call void (...) @llvm.experimental.deoptimize.isVoid(i32 0) [ "deopt"() ]
+; CHECK-NEXT:    ret void
+;
 bb:
   %wc1 = call i1 @llvm.experimental.widenable.condition()
   %wc2 = call i1 @llvm.experimental.widenable.condition()
   %zero = add i32 0, 0
   %check = icmp ult i32 %zero, 0
   %c1 = and i1 %check, %wc1
   %c2 = and i1 %check, %wc2
   br i1 %c1, label %bb6, label %bb9