SpeculativeExecution: Fix for logic change introduced in D81730.

Summary:
The test case started to hoist bitcasts to upper BB after D81730.
Reverted unintentional logic change. Some instructions may have zero cost but
will not be hoisted by different limitation so should be counted for threshold.

Reviewers: aprantl, arsenm, nhaehnle

Reviewed By: aprantl

Subscribers: wdng, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D82761

Author: dfukalov

llvm/lib/Transforms/Scalar/SpeculativeExecution.cpp

@@ -291,10 +291,8 @@ bool SpeculativeExecutionPass::considerHoistingFromTo(
       if (TotalSpeculationCost > SpecExecMaxSpeculationCost)
         return false;  // too much to hoist
     } else {
-      // If the instruction cannot be hoisted but has zero cost suppose it's
-      // a special case e.g. debug info instrinsics that should not be counted
-      // for threshold.
-      if (Cost)
+      // Debug info instrinsics should not be counted for threshold.
+      if (!isa<DbgInfoIntrinsic>(I))
         NotHoistedInstCount++;
       if (NotHoistedInstCount > SpecExecMaxNotHoisted)
         return false; // too much left behind

llvm/test/Transforms/SpeculativeExecution/PR46267.ll

@@ -1,6 +1,36 @@
 ; RUN: opt < %s -S -speculative-execution | FileCheck %s
 ; RUN: opt < %s -S -passes='speculative-execution' | FileCheck %s
 
+%class.B = type { i32 (...)** }
+
+; Testing that two bitcasts are not hoisted to the first BB
+define i8* @foo(%class.B* readonly %b) {
+; CHECK-LABEL: foo
+; CHECK-LABEL: entry
+; CHECK-NEXT: %i = icmp eq %class.B* %b, null
+; CHECK-NEXT: br i1 %i, label %end, label %notnull
+entry:
+  %i = icmp eq %class.B* %b, null
+  br i1 %i, label %end, label %notnull
+
+; CHECK-LABEL: notnull:
+; CHECK-NEXT: %i1 = bitcast %class.B* %b to i32**
+; CHECK: %i3 = bitcast %class.B* %b to i8*
+notnull:                             ; preds = %entry
+  %i1 = bitcast %class.B* %b to i32**
+  %vtable = load i32*, i32** %i1, align 8
+  %i2 = getelementptr inbounds i32, i32* %vtable, i64 -2
+  %offset.to.top = load i32, i32* %i2, align 4
+  %i3 = bitcast %class.B* %b to i8*
+  %i4 = sext i32 %offset.to.top to i64
+  %i5 = getelementptr inbounds i8, i8* %i3, i64 %i4
+  br label %end
+
+end:                                 ; preds = %notnull, %entry
+  %i6 = phi i8* [ %i5, %notnull ], [ null, %entry ]
+  ret i8* %i6
+}
+
 define void @f(i32 %i) {
 entry:
 ; CHECK-LABEL: @f(